Home Fertilizers In animal cells among organic ones. Organic substances of living systems. Structure and functions of biological membranes

Fertilizers

In animal cells among organic ones. Organic substances of living systems. Structure and functions of biological membranes

They make up 20-30% of the cell mass. These include biopolymers - proteins, nucleic acids, carbohydrates, fats, ATP, etc.

Different types of cells contain different amounts of organic compounds. Complex carbohydrates predominate in plant cells, while proteins and fats predominate in animal cells. Nevertheless, each group of organic substances in any type of cells performs functions: providing energy, is building material, carries information, etc.

Squirrels. Among organic substances, cells and proteins occupy first place in quantity and importance. In animals they account for 50% of the dry mass of the cell.

The human body contains many types of protein molecules that differ from each other and from proteins in other organisms.

Peptide bond:

The sequence of amino acids in a molecule is called structure.

Primary – linear.

Secondary – spiral.

Tertiary - globules.

Quaternary - association of globules (hemoglobin).

The loss of structural organization by a molecule is called denaturation. It is caused by changes in temperature, pH, and radiation. With minor exposure, the molecule can restore its properties. It is used in medicine (antibiotics).

The functions of proteins in a cell are diverse. The most important is construction. Proteins are involved in the formation of all cell membranes in organelles. The catalytic function is extremely important - all enzymes are proteins. Motor function is provided by contractile proteins. Transport - consists of attaching chemical elements and transferring them to tissues. The protective function is provided by special proteins - antibodies formed in leukocytes. Proteins serve as a source of energy - with the complete breakdown of 1g of protein, 11.6 kJ is released.

Carbohydrates. These are compounds of carbon, hydrogen and oxygen. Represented by sugars. The cell contains up to 5%. The richest are plant cells - up to 90% of the mass (potatoes, rice). They are divided into simple and complex. Simple - monosaccharides (glucose) C 6 H 12 O 6, grape sugar, fructose. Disaccharide – (sucrose) C ]2 H 22 O 11 beet and cane sugar. Polysugars (cellulose, starch) (C 6 H 10 O 5)n.

Carbohydrates perform mainly construction and energy function. When 1g of carbohydrate is oxidized, 17.6 kJ is released. Starch and glycogen serve as the cell's energy reserves.

Lipids. These are fats and fat-like substances in the cell. They are esters of glycerol and high molecular weight saturated and unsaturated acids. They can be solid or liquid – oils. In plants they are contained in seeds, from 5-15% of dry matter.

The main function is energy - when 1g of fat is broken down, 38.9 kJ is released. Fats are nutrient reserves. Fats perform a construction function and are a good heat insulator.

Nucleic acids. It's complicated organic compounds. They consist of C, H 2, O 2, N 2, P. Contained in the nuclei and cytoplasm.

a) DNA is a biological polynucleotide consisting of two chains of nucleotides. Nucleotides - consist of 4 nitrogenous bases: 2 purines - Adenine and Valine, 2 pyrimedines Cytosine and Guanine, as well as sugar - deoxyribose and a phosphoric acid residue.

In each chain, nucleotides are connected by covalent bonds. Chains of nucleotides form helices. A DNA helix packed with proteins forms a structure - a chromosome.

b) RNA is a polymer whose monomers are nucleotides similar to DNA, nitrogenous bases - A, G, C. Instead of thymine there is Urace. The carbohydrate in RNA is ribose and there is a phosphoric acid residue.

Double-stranded RNAs are carriers of genetic information. Single-chain - carry information about the sequence of amino acids in a protein. There are several single-stranded RNAs:

Ribosomal – 3-5 thousand nucleotides;

Informational – 300-30000 nucleotides;

Transport - 76-85 nucleotides.

Protein synthesis is carried out on ribosomes with the participation of all types of RNA.

Control questions

1. Is a cell an organism or a part of it?

2. Elementary composition of cells.

3. Water and minerals.

4. Organic substances of the cell.

Animals, fungi and bacteria

Sign	Bacteria	Animals	Mushrooms	Plants
Nutrition method	Heterotrophic or autotrophic	Heterotrophic	Heterotrophic	Autotrophic
Organization hereditary information	Prokaryotes	Eukaryotes	Eukaryotes	Eukaryotes
DNA localization	Nucleoid, plasmids	Nucleus, mitochondria	Nucleus, mitochondria	Nucleus, mitochondria, plastids
Plasma membrane	Eat	Eat	Eat	Eat
Cell wall	Mureinovaya	-	Chitinous	Pulp
Cytoplasm	Eat	Eat	Eat	Eat
Organoids	Ribosomes	Membrane and non-membrane, including the cell center	Membrane and non-membrane	Membrane and non-membrane, including plastids
Organoids of movement	Flagella and villi	Flagella and cilia	Flagella and cilia	Flagella and cilia
Vacuoles	Rarely	Contractile, digestive	Sometimes	Central vacuole with cell sap
Inclusions	Volyutin	Glycogen	Glycogen	Starch

Differences in the structure of cells of representatives of different kingdoms of living nature are shown in Fig. 2.3.

Rice. 2.3. The structure of bacterial cells (A), animals (B), fungi (C) and plants (D)
2.3. Chemical organization of the cell. The relationship between the structure and functions of inorganic and organic substances (proteins, nucleic acids, carbohydrates, lipids, ATP) that make up the cell. Justification of the relationship of organisms based on an analysis of the chemical composition of their cells.
Chemical composition of the cell.

Most of the chemical elements of D.I. Mendeleev’s Periodic Table of Elements discovered to date have been found in living organisms. On the one hand, they do not contain a single element that would not be found in inanimate nature, and on the other hand, their concentrations in bodies of inanimate nature and living organisms differ significantly (Table 2.2).

These chemical elements form inorganic and organic substances. Despite the fact that living organisms are dominated by inorganic substances(Fig. 2.4), it is organic substances that determine the uniqueness of their chemical composition and the phenomenon of life as a whole, since they are synthesized mainly by organisms in the process of life and play a vital role in reactions.

Science studies the chemical composition of organisms and the chemical reactions occurring in them. biochemistry.

It should be noted that the content of chemicals in different cells and tissues can vary significantly. For example, if in animal cells proteins predominate among organic compounds, then in plant cells carbohydrates predominate.

Table 2.2

Content of some chemical elements in inanimate nature and living organisms, %

Chemical element	Earth's crust	Sea water	Alive organisms
ABOUT	49,2	85,8	65-75
WITH	0,4	0,0035	15-18
N	1,0	10,67	8-10
N	0,04	0,37	1,5-3,0
R	0,1	0,003	0,20-1,0
S	0,15	0,09	0,15-0,2
TO	2,35	0,04	0,15-0,4
Sa	3,25	0,05	0,04-2,0
C1	0,2	0,06	0,05-0,1
Mg	2,35	0,14	0,02-0,03
Na	2,4	1.14	0,02-0,03
Fe	4,2	0,00015	0,01-0,015
Zn		0,00015	0,0003
Cu			0,0002
I		0,000015	0,0001
F	0,1	2,07	0,0001

Macro- and microelements

About 80 chemical elements are found in living organisms, but only 27 of these elements have their functions in the cell and organism established. The remaining elements are present in small quantities and, apparently, enter the body with food, water and air. The content of chemical elements in the body varies significantly (see Table 2.2). Depending on their concentration, they are divided into macroelements and microelements.

The concentration of each macronutrients in the body exceeds 0.01%, and their total content is 99%. Macroelements include oxygen, carbon, hydrogen, nitrogen, phosphorus, sulfur, potassium, calcium, sodium, chlorine, magnesium and iron. The first four of the listed elements (oxygen, carbon, hydrogen and nitrogen) are also called organogenic, since they are part of the main organic compounds. Phosphorus and sulfur are also components of a number of organic substances, such as proteins and nucleic acids. Phosphorus is essential for the formation of bones and teeth.

Without the remaining macroelements, normal functioning of the body is impossible. Thus, potassium, sodium and chlorine are involved in the processes of cell excitation. Potassium is also necessary for the functioning of many enzymes and the retention of water in the cell. Calcium is found in the cell walls of plants, bones, teeth, and mollusk shells and is required for muscle cell contraction and intracellular movement. Magnesium is a component of chlorophyll, a pigment that ensures photosynthesis occurs. It also takes part in protein biosynthesis. Iron, in addition to being part of hemoglobin, which carries oxygen in the blood, is necessary for the processes of respiration and photosynthesis, as well as for the functioning of many enzymes.

Microelements are contained in the body in concentrations of less than 0.01%, and their total concentration in the cell does not reach 0.1%. Microelements include zinc, copper, manganese, cobalt, iodine, fluorine, etc. Zinc is part of the molecule of the pancreatic hormone - insulin, copper is required for the processes of photosynthesis and respiration. Cobalt is a component of vitamin B 12, the absence of which leads to anemia. Iodine is necessary for hormone synthesis thyroid gland, ensuring normal metabolism, and fluoride is associated with the formation of tooth enamel.

Both deficiency and excess or disruption of the metabolism of macro- and microelements lead to the development various diseases. In particular, a lack of calcium and phosphorus causes rickets, a lack of nitrogen - severe protein deficiency, a deficiency of iron - anemia, and a lack of iodine - a violation of the formation of thyroid hormones and a decrease in metabolic rate. A decrease in fluoride intake from water and food largely determines the disruption of tooth enamel renewal and, as a consequence, a predisposition to caries. Lead is toxic to almost all organisms. Its excess causes irreversible damage to the brain and central nervous system, which is manifested by loss of vision and hearing, insomnia, kidney failure, seizures, and can also lead to paralysis and diseases such as cancer. Acute lead poisoning is accompanied by sudden hallucinations and ends in coma and death.

Rice. 2.4. Content of chemicals in the cell
The lack of macro- and microelements can be compensated by increasing their content in food and drinking water, as well as through taking medications. Thus, iodine is found in seafood and iodized salt, calcium is found in eggshells, etc.

2.3.1. Inorganic substances of the cell.
The chemical elements of the cell form various compounds - inorganic and organic. The inorganic substances of the cell include water, mineral salts, acids, etc., and the organic substances include proteins, nucleic acids, carbohydrates, lipids, ATP, vitamins, etc. (Fig. 2.4).

Water (H 2 0) is the most common inorganic substance of the cell, which has unique physicochemical properties. It has no taste, no color, no smell. The density and viscosity of all substances is assessed using water. Like many other substances, water can exist in three states of aggregation: solid (ice), liquid and gaseous (steam). The melting point of water is 0°C, the boiling point is 100°C, however, the dissolution of other substances in water can change these characteristics. The heat capacity of water is also quite high - 4200 kJ/mol. K, which gives it the opportunity to take part in thermoregulation processes. In a water molecule, the hydrogen atoms are located at an angle of 105°, with shared electron pairs pulled away by the more electronegative oxygen atom. This determines the dipole properties of water molecules (one end is positively charged and the other negatively charged) and the possibility of the formation of hydrogen bonds between water molecules (Fig. 2.5). The cohesion of water molecules underlies the phenomenon of surface tension, capillarity and the properties of water as a universal solvent. As a result, all substances are divided into soluble in water (hydrophilic) and insoluble in it (hydrophobic). Thanks to these unique properties, it is predetermined that water has become the basis of life on Earth.

The average water content in the body's cells varies and may change with age. Thus, in a one-and-a-half-month-old human embryo, the water content in the cells reaches 97.5%, in an eight-month-old - 83%, in a newborn it decreases to 74%, and in an adult it averages 66%. However, body cells differ in their water content. So, the bones contain about 20% water, the liver - 70%, and the brain - 86%. In general it can be said that the concentration of water in cells is directly proportional to the metabolic rate.

Mineral salts can be in dissolved or undissolved states. Soluble salts dissociate into ions - cations and anions. The most important cations are potassium and sodium ions, which facilitate the transfer of substances across the membrane and are involved in the occurrence and conduction of nerve impulses; as well as calcium ions, which takes part in the processes of muscle fiber contraction and blood clotting; magnesium, which is part of chlorophyll; iron, which is part of a number of proteins, including hemoglobin. The most important anions are the phosphate anion, which is part of ATP and nucleic acids, and the residue carbonic acid, softening fluctuations in the pH of the environment. Ions of mineral salts ensure the penetration of water itself into the cell and its retention in it. If the salt concentration in the environment is lower than in the cell, then water penetrates into the cell. Ions also determine the buffering properties of the cytoplasm, i.e. its ability to maintain a constant slightly alkaline pH of the cytoplasm, despite the constant formation of acidic and alkaline products in the cell.

Insoluble salts(CaC0 3, Ca 3 (P0 4) 2, etc.) are part of the bones, teeth, shells and shells of unicellular and multicellular animals.

In addition, organisms can produce other inorganic compounds, such as acids and oxides. Thus, the parietal cells of the human stomach produce hydrochloric acid, which activates the digestive enzyme pepsin, and silicon oxide permeates the cell walls of horsetails and forms the shells of diatoms. IN last years The role of nitric oxide (II) in signaling in cells and the body is also being explored.

Organic substances in a cell They make up 20-30% of the cell mass. These include biopolymers - proteins, nucleic acids, carbohydrates, fats, ATP, etc. Different types of cells contain different amounts of organic compounds. Complex carbohydrates predominate in plant cells, while proteins and fats predominate in animal cells. Nevertheless, each group of organic substances in any type of cell performs functions: providing energy, being a building material, carrying information, etc. Squirrels. Among organic substances, cells and proteins occupy first place in quantity and importance. In animals they account for 50% of the dry mass of the cell. In the human body, there are many types of protein molecules that differ from each other and from the proteins of other organisms. Despite the enormous diversity and complexity of structure, proteins are built from 20 amino acids: Amino acids have amphoteric properties, therefore they interact with each other:

Peptide bond:

When combined, the molecules form: a dipeptide, tripeptide or polypeptide. This is a compound of 20 or more amino acids. The order of transformation of amino acids in a molecule is very diverse. This allows existence
options that differ in the requirements and properties of protein molecules. The sequence of amino acids in a molecule is called structure. Primary – linear. Secondary – spiral. Tertiary - globules. Quaternary - association of globules (hemoglobin). The loss of structural organization by a molecule is called denaturation. It is caused by changes in temperature, pH, and radiation. With minor exposure, the molecule can restore its properties. It is used in medicine (antibiotics). The functions of proteins in a cell are diverse. The most important is construction. Proteins are involved in the formation of all cell membranes in organelles. The catalytic function is extremely important - all enzymes are proteins. Motor function is provided by contractile proteins. Transport - consists of attaching chemical elements and transferring them to tissues. The protective function is provided by special proteins - antibodies formed in leukocytes. Proteins serve as a source of energy - with the complete breakdown of 1g of protein, 11.6 kJ is released. Carbohydrates. These are compounds of carbon, hydrogen and oxygen. Represented by sugars. The cell contains up to 5%. The richest are plant cells - up to 90% of the mass (potatoes, rice). They are divided into simple and complex. Simple - monosaccharides (glucose) C 6 H 12 O 6, grape sugar, fructose. Disaccharide – (sucrose) C ]2 H 22 O 11 beet and cane sugar. Polysugars (cellulose, starch) (C 6 H 10 O 5)n. Carbohydrates perform mainly construction and energy functions. When 1g of carbohydrate is oxidized, 17.6 kJ is released. Starch and glycogen serve as the cell's energy reserves. Lipids. These are fats and fat-like substances in the cell. They are esters of glycerol and high molecular weight saturated and unsaturated acids. They can be solid or liquid – oils. In plants they are contained in seeds, from 5-15% of dry matter. The main function is energy - when 1g of fat is broken down, 38.9 kJ is released. Fats are nutrient reserves. Fats perform a construction function and are a good heat insulator. Nucleic acids. These are complex organic compounds. They consist of C, H 2, O 2, N 2, P. Contained in the nuclei and cytoplasm.
a) DNA is a biological polynucleotide consisting of two chains of nucleotides. Nucleotides - consist of 4 nitrogenous bases: 2 purines - Adenine and Valine, 2 pyrimedines Cytosine and Guanine, as well as sugar - deoxyribose and a phosphoric acid residue. In each chain, nucleotides are connected by covalent bonds. Chains of nucleotides form helices. A DNA helix packed with proteins forms a structure - a chromosome. b) RNA is a polymer whose monomers are nucleotides similar to DNA, nitrogenous bases - A, G, C. Instead of thymine there is Urace. The carbohydrate in RNA is ribose and there is a phosphoric acid residue.

Double-stranded RNAs are carriers of genetic information. Single-chain - carry information about the sequence of amino acids in a protein. There are several single-stranded RNAs: - Ribosomal - 3-5 thousand nucleotides; - Informational – 300-30000 nucleotides; - Transport – 76-85 nucleotides. Protein synthesis is carried out on ribosomes with the participation of all types of RNA.

Control questions

1. Is a cell an organism or a part of it? 2. Elementary composition of cells. 3. Water and minerals. 4. Organic substances of the cell. 5. Proteins. 6. Carbohydrates, fats. 7. DNA. 8. RNA.

Topic 2.2 Cell structure and functions

Control questions

1. What is meant by the level of cell organization? 2. Characteristics of prokaryotes and eukaryotes. 3. The structure of prokaryotes. 4. Morphology of prokaryotes. 5. The structure of eukaryotes. 6. Structure and functions of the nucleus. 7. Karyotype and its features. 8. Structure and functions of the nucleolus. Topic 2.2.1 Golgi complex, lysosomes, mitochondria,

ribosomes, cell center; movement organoids

Cytoplasm- This is the internal semi-liquid environment of the cell in which all biochemical processes take place. It contains structures - organelles and communicates between them. Organelles have regular features of structure and behavior during different periods of cell life and perform certain functions. There are organelles characteristic of all cells - mitochondria, cell center, Golgi apparatus, ribosomes, EPS, lysosomes. Organelles of movement - flagella and cilia are characteristic of unicellular organisms. Various substances - inclusions - are deposited in the cytoplasm. These are permanent structures that arise in the process of life. Dense inclusions are granules, liquid inclusions are vacuoles. Their size is determined by the vital activity of cells. The structural organization of the cell is based on membrane principle buildings. This means that the cell is mainly made of membranes. All membranes have a similar structure. The accepted model is a liquid-mosaic structure: the membrane is formed by two rows of lipids into which protein molecules are immersed at different depths. Outer cytoplasmic membrane It is present in all cells and separates the cytoplasm from the external environment, forming the cell surface. The surface of the cell is heterogeneous, its physiological properties are different. The cell has high strength and elasticity. The cytoplasmic membrane has pores through which molecules of substances pass. The entry of substances into the cell is a process that requires energy consumption. The cell membrane has the property of semi-permeability. The mechanism providing semi-permeability is osmosis. In addition to osmosis, chemicals and solids can enter the cell through protrusions - pinocetosis and phagocytosis. The cytoplasmic membrane also provides communication between cells in the tissues of multicellular organisms due to numerous folds and outgrowths.

Cell as a biological system

Modern cell theory, its main provisions, role in the formation of the modern natural science picture of the world. Development of knowledge about the cell. The cellular structure of organisms is the basis of the unity of the organic world, proof of the kinship of living nature

Modern cell theory, its main provisions, role in the formation of the modern natural science picture of the world

One of the fundamental concepts in modern biology is the idea that all living organisms have a cellular structure. Science studies the structure of a cell, its life activity and interaction with the environment. cytology, now more commonly referred to as cell biology. Cytology owes its appearance to the formulation of the cell theory (1838-1839, M. Schleiden, T. Schwann, supplemented in 1855 by R. Virchow).

Cell theory is a generalized idea of the structure and functions of cells as living units, their reproduction and role in the formation of multicellular organisms.

Basic principles of cell theory:

A cell is a unit of structure, vital activity, growth and development of living organisms - there is no life outside the cell.
A cell is a single system consisting of many elements naturally interconnected with each other, representing a certain integral formation.
The cells of all organisms are similar in their chemical composition, structure and functions.
New cells are formed only as a result of the division of mother cells (“cell from cell”).
The cells of multicellular organisms form tissues, and organs are made up of tissues. The life of an organism as a whole is determined by the interaction of its constituent cells.
Cells of multicellular organisms have a full set of genes, but differ from each other in that different groups of genes work in them, which results in morphological and functional diversity of cells - differentiation.

Thanks to the creation of the cellular theory, it became clear that the cell is the smallest unit of life, an elementary living system, which has all the signs and properties of living things. The formulation of the cell theory became the most important prerequisite for the development of views on heredity and variability, since the identification of their nature and inherent patterns inevitably suggested the universality of the structure of living organisms. The identification of the unity of the chemical composition and structure of cells served as an impetus for the development of ideas about the origin of living organisms and their evolution. In addition, the origin of multicellular organisms from a single cell during embryonic development has become a dogma of modern embryology.

Development of knowledge about the cell

Until the 17th century, people knew nothing at all about the microstructure of the objects around them and perceived the world with the naked eye. A device for studying the microworld - the microscope - was invented around 1590 by the Dutch mechanics G. and Z. Jansen, but its imperfection did not make it possible to examine sufficiently small objects. Only the creation on its basis of the so-called compound microscope by K. Drebbel (1572-1634) contributed to progress in this area.

In 1665, the English physicist R. Hooke (1635-1703) improved the design of the microscope and the technology of grinding lenses and, wanting to make sure the image quality was improved, examined sections of cork underneath it, charcoal and living plants. On the sections, he discovered tiny pores, reminiscent of a honeycomb, and called them cells (from the Latin. cellulum- cell, cell). It is interesting to note that R. Hooke considered the cell membrane to be the main component of the cell.

In the second half of the 17th century, the works of the most prominent microscopists M. Malpighi (1628-1694) and N. Grew (1641-1712) appeared, who also discovered the cellular structure of many plants.

To make sure that what R. Hooke and other scientists saw was true, the Dutch trader A. van Leeuwenhoek, who had no special education, independently developed a microscope design that was fundamentally different from the existing one, and improved the lens manufacturing technology. This allowed him to achieve a magnification of 275-300 times and examine structural details that were technically inaccessible to other scientists. A. van Leeuwenhoek was an unsurpassed observer: he carefully sketched and described what he saw under the microscope, but did not seek to explain it. He discovered single-celled organisms, including bacteria, and found nuclei, chloroplasts, and thickening of cell walls in plant cells, but his discoveries were appreciated much later.

Component openings internal structure organisms in the first half of the 19th century followed one after another. G. Mohl distinguished living matter and watery liquid - cell sap - in plant cells, and discovered pores. The English botanist R. Brown (1773-1858) discovered the nucleus in orchid cells in 1831, then it was discovered in all plant cells. The Czech scientist J. Purkinje (1787-1869) coined the term “protoplasm” to designate the semi-liquid gelatinous contents of a cell without a nucleus (1840). The Belgian botanist M. Schleiden (1804-1881) advanced further than all his contemporaries, who, while studying the development and differentiation of various cellular structures higher plants, proved that all plant organisms originate from a single cell. He also examined rounded nucleoli bodies in the nuclei of onion scale cells (1842).

In 1827, the Russian embryologist K. Baer discovered eggs of humans and other mammals, thereby refuting the idea of the development of an organism exclusively from male gametes. In addition, he proved the formation of a multicellular animal organism from a single cell - a fertilized egg, as well as the similarity of the stages of embryonic development of multicellular animals, which suggested the unity of their origin. The information accumulated by the middle of the 19th century required generalization, which became the cell theory. Biology owes its formulation to the German zoologist T. Schwann (1810-1882), who, based on his own data and M. Schleiden’s conclusions about the development of plants, put forward the assumption that if a nucleus is present in any formation visible under a microscope, then this formation is cell. Based on this criterion, T. Schwann formulated the main provisions of the cell theory.

The German physician and pathologist R. Virchow (1821-1902) introduced another important point into this theory: cells arise only by dividing the original cell, i.e. cells are formed only from cells (“cell from cell”).

Since the creation of cell theory, the doctrine of the cell as a unit of structure, function and development of an organism has been continuously developing. By the end of the 19th century, thanks to the successes of microscopic technology, the structure of the cell was clarified, organelles—cell parts that perform various functions—were described, methods of formation of new cells (mitosis, meiosis) were studied, and the primary importance of cellular structures in the transmission of hereditary properties became clear. The use of the latest physicochemical research methods made it possible to delve deeper into the processes of storage and transmission of hereditary information, as well as to study the fine structure of each of the cell structures. All this contributed to the separation of cell science into an independent branch of knowledge - cytology.

The cellular structure of organisms, the similarity of the structure of the cells of all organisms is the basis of the unity of the organic world, evidence of the kinship of living nature

All living organisms known today (plants, animals, fungi and bacteria) have a cellular structure. Even viruses that do not have a cellular structure can only reproduce in cells. A cell is an elementary structural and functional unit of a living thing, which is characterized by all its manifestations, in particular, metabolism and energy conversion, homeostasis, growth and development, reproduction and irritability. At the same time, it is in the cells that hereditary information is stored, processed and implemented.

Despite all the diversity of cells, the structural plan for them is the same: they all contain hereditary apparatusimmersed in cytoplasm, and the surrounding cell plasma membrane.

The cell arose as a result of the long evolution of the organic world. The union of cells into a multicellular organism is not a simple summation, since each cell, while retaining all the characteristics inherent in a living organism, at the same time acquires new properties due to its performance of a specific function. On the one hand, a multicellular organism can be divided into its constituent parts - cells, but on the other hand, by putting them back together, it is impossible to restore the functions of the entire organism, since only in the interaction of parts of the system do new properties appear. This reveals one of the main patterns that characterize living things - the unity of the discrete and the holistic. Small size and significant amount cells create in multicellular organisms a large surface area necessary to ensure rapid metabolism. In addition, if one part of the body dies, its integrity can be restored through cell reproduction. Outside the cell, storage and transmission of hereditary information, storage and transfer of energy with its subsequent conversion into work are impossible. Finally, the division of functions between cells in a multicellular organism provided ample opportunities for organisms to adapt to their environment and was a prerequisite for increasing the complexity of their organization.

Thus, the establishment of the unity of the structural plan of the cells of all living organisms served as proof of the unity of origin of all life on Earth.

Diversity of cells. Prokaryotic and eukaryotic cells. Comparative characteristics of cells of plants, animals, bacteria, fungi Diversity of cells

According to cellular theory, a cell is the smallest structural and functional unit of organisms, which has all the properties of a living thing. Based on the number of cells, organisms are divided into unicellular and multicellular. Cells of unicellular organisms exist as independent organisms and perform all the functions of living things. All prokaryotes and a number of eukaryotes (many types of algae, fungi and protozoa) are unicellular, which amaze with their extraordinary variety of shapes and sizes. However, most organisms are still multicellular. Their cells specialize in performing certain functions and form tissues and organs, which cannot but affect their morphological features. For example, the human body is formed from approximately 10 14 cells, represented by approximately 200 species, having a wide variety of shapes and sizes.

The shape of cells can be round, cylindrical, cubic, prismatic, disc-shaped, spindle-shaped, stellate, etc. Thus, eggs have a round shape, epithelial cells have a cylindrical, cubic and prismatic shape, red blood cells have the shape of a biconcave disk, and spindle-shaped cells muscle tissue, and stellate - cells of nervous tissue. A number of cells have no permanent shape at all. These include, first of all, blood leukocytes.

Cell sizes also vary significantly: most cells of a multicellular organism have sizes from 10 to 100 microns, and the smallest - 2-4 microns. The lower limit is due to the fact that the cell must have a minimum set of substances and structures to ensure vital activity, and too large a cell size will interfere with the exchange of substances and energy with the environment, and will also complicate the processes of maintaining homeostasis. However, some cells can be seen with the naked eye. First of all, these include the cells of watermelon and apple fruits, as well as the eggs of fish and birds. Even if one of the linear dimensions of the cell exceeds the average, all the others correspond to the norm. For example, the process of a neuron can exceed 1 m in length, but its diameter will still correspond to the average value. There is no direct relationship between cell size and body size. Thus, the muscle cells of an elephant and a mouse are the same size.

Prokaryotic and eukaryotic cells

As mentioned above, cells have many similar functional properties and morphological features. Each of them consists of cytoplasm immersed in it hereditary apparatus, and separated from the external environment plasma membrane, or plasmalemma, which does not interfere with the process of metabolism and energy. Outside the membrane, the cell may also have a cell wall, consisting of various substances, which serves to protect the cell and is a kind of external skeleton.

Cytoplasm is the entire contents of a cell, filling the space between the plasma membrane and the structure containing genetic information. It consists of the main substance - hyaloplasma- and organelles and inclusions immersed in it. Organoids are permanent components of the cell that perform certain functions, and inclusions are components that appear and disappear during the life of the cell, primarily performing storage or excretory functions. Inclusions are often divided into solid and liquid. Solid inclusions are mainly represented by granules and can be of different nature, while vacuoles and fat droplets are considered liquid inclusions.

Currently, there are two main types of cell organization: prokaryotic and eukaryotic.

A prokaryotic cell does not have a nucleus; its genetic information is not separated from the cytoplasm by membranes.

The region of the cytoplasm in which genetic information is stored in a prokaryotic cell is called nucleoid. In the cytoplasm prokaryotic cells There is mainly one type of organelle - ribosomes, and organelles surrounded by membranes are completely absent. Bacteria are prokaryotes.

A eukaryotic cell is a cell in which at least one of the stages of development has core- a special structure in which DNA is located.

The cytoplasm of eukaryotic cells is distinguished by a significant diversity of membrane and non-membrane organelles. Eukaryotic organisms include plants, animals and fungi. The size of prokaryotic cells is usually an order of magnitude smaller than the size of eukaryotic cells. Most prokaryotes are unicellular organisms, while eukaryotes are multicellular.

Comparative characteristics of the structure of cells of plants, animals, bacteria and fungi

In addition to the features characteristic of prokaryotes and eukaryotes, the cells of plants, animals, fungi and bacteria also have a number of features. Thus, plant cells contain specific organelles - chloroplasts, which determine their ability to photosynthesize, whereas these organelles are not found in other organisms. Of course, this does not mean that other organisms are not capable of photosynthesis, since, for example, in bacteria it occurs on invaginations of the plasma membrane and individual membrane vesicles in the cytoplasm.

Plant cells, as a rule, contain large vacuoles filled with cell sap. They are also found in the cells of animals, fungi and bacteria, but have a completely different origin and perform different functions. The main reserve substance found in the form of solid inclusions in plants is starch, in animals and fungi it is glycogen, and in bacteria it is glycogen or volutin.

Another distinctive feature of these groups of organisms is the organization of the surface apparatus: the cells of animal organisms do not have a cell wall, their plasma membrane is covered only with a thin glycocalyx, while all others have it. This is entirely understandable, since the way animals feed is associated with the capture of food particles during the process of phagocytosis, and the presence of a cell wall would deprive them of this opportunity. The chemical nature of the substance that makes up the cell wall is different in different groups of living organisms: if in plants it is cellulose, then in fungi it is chitin, and in bacteria it is murein. Comparative characteristics of the structure of cells of plants, animals, fungi and bacteria

Sign	Bacteria	Animals	Mushrooms	Plants
Nutrition method	Heterotrophic or autotrophic	Heterotrophic	Heterotrophic	Autotrophic
Organization of hereditary information	Prokaryotes	Eukaryotes	Eukaryotes	Eukaryotes
DNA localization	Nucleoid, plasmids	Nucleus, mitochondria	Nucleus, mitochondria	Nucleus, mitochondria, plastids
Plasma membrane	Eat	Eat	Eat	Eat
Cell wall	Mureinovaya	—	Chitinous	Pulp
Cytoplasm	Eat	Eat	Eat	Eat
Organoids	Ribosomes	Membrane and non-membrane, including the cell center	Membrane and non-membrane	Membrane and non-membrane, including plastids
Organoids of movement	Flagella and villi	Flagella and cilia	Flagella and cilia	Flagella and cilia
Vacuoles	Rarely	Contractile, digestive	Sometimes	Central vacuole with cell sap
Inclusions	Glycogen, volutin	Glycogen	Glycogen	Starch

The differences in the structure of cells of representatives of different kingdoms of living nature are shown in the figure.

Chemical composition of the cell. Macro- and microelements. The relationship between the structure and functions of inorganic and organic substances (proteins, nucleic acids, carbohydrates, lipids, ATP) that make up the cell. The role of chemicals in the cell and human body

Chemical composition of the cell

These chemical elements form inorganic and organic substances. Despite the fact that inorganic substances predominate in living organisms, it is organic substances that determine the uniqueness of their chemical composition and the phenomenon of life as a whole, since they are synthesized mainly by organisms in the process of life and play a vital role in reactions.

Science studies the chemical composition of organisms and the chemical reactions occurring in them. biochemistry.

Chemical element	Earth's crust	Sea water	Alive organisms
O	49.2	85.8	65-75
C	0.4	0.0035	15-18
H	1.0	10.67	8-10
N	0.04	0.37	1.5-3.0
P	0.1	0.003	0.20-1.0
S	0.15	0.09	0.15-0.2
K	2.35	0.04	0.15-0.4
Ca	3.25	0.05	0.04-2.0
Cl	0.2	0.06	0.05-0.1
Mg	2.35	0.14	0.02-0.03
Na	2.4	1.14	0.02-0.03
Fe	4.2	0.00015	0.01-0.015
Zn	< 0.01	0.00015	0.0003
Cu	< 0.01	< 0.00001	0.0002
I	< 0.01	0.000015	0.0001
F	0.1	2.07	0.0001

Macro- and microelements

About 80 chemical elements are found in living organisms, but only 27 of these elements have their functions in the cell and organism established. The remaining elements are present in small quantities and, apparently, enter the body with food, water and air. The content of chemical elements in the body varies significantly. Depending on their concentration, they are divided into macroelements and microelements.

The concentration of each macronutrients in the body exceeds 0.01%, and their total content is 99%. Macroelements include oxygen, carbon, hydrogen, nitrogen, phosphorus, sulfur, potassium, calcium, sodium, chlorine, magnesium and iron. The first four of the listed elements (oxygen, carbon, hydrogen and nitrogen) are also called organogenic, since they are part of the main organic compounds. Phosphorus and sulfur are also components of a number of organic substances, such as proteins and nucleic acids. Phosphorus is essential for the formation of bones and teeth.

Without the remaining macroelements, normal functioning of the body is impossible. Thus, potassium, sodium and chlorine are involved in the processes of cell excitation. Potassium is also necessary for the functioning of many enzymes and the retention of water in the cell. Calcium is found in the cell walls of plants, bones, teeth, and mollusk shells and is required for muscle cell contraction and intracellular movement. Magnesium is a component of chlorophyll, a pigment that allows photosynthesis to occur. It also takes part in protein biosynthesis. Iron, in addition to being part of hemoglobin, which carries oxygen in the blood, is necessary for the processes of respiration and photosynthesis, as well as for the functioning of many enzymes.

Microelements are contained in the body in concentrations of less than 0.01%, and their total concentration in the cell does not reach 0.1%. Microelements include zinc, copper, manganese, cobalt, iodine, fluorine, etc. Zinc is part of the molecule of the pancreatic hormone insulin, copper is required for the processes of photosynthesis and respiration. Cobalt is a component of vitamin B12, the absence of which leads to anemia. Iodine is necessary for the synthesis of thyroid hormones, which ensure normal metabolism, and fluoride is associated with the formation of tooth enamel.

Both deficiency and excess or disturbance of the metabolism of macro- and microelements lead to the development of various diseases. In particular, a lack of calcium and phosphorus causes rickets, a lack of nitrogen causes severe protein deficiency, a deficiency of iron causes anemia, and a lack of iodine causes a disruption in the formation of thyroid hormones and a decrease in metabolic rate. A decrease in fluoride intake from water and food largely determines the disruption of tooth enamel renewal and, as a consequence, a predisposition to caries. Lead is toxic to almost all organisms. Its excess causes irreversible damage to the brain and central nervous system, which is manifested by loss of vision and hearing, insomnia, kidney failure, seizures, and can also lead to paralysis and diseases such as cancer. Acute lead poisoning is accompanied by sudden hallucinations and ends in coma and death.

The lack of macro- and microelements can be compensated by increasing their content in food and drinking water, as well as by taking medications. Thus, iodine is found in seafood and iodized salt, calcium is found in eggshells, etc.

The relationship between the structure and functions of inorganic and organic substances (proteins, nucleic acids, carbohydrates, lipids, ATP) that make up the cell. The role of chemicals in the cell and human body

Inorganic substances

The chemical elements of the cell form various compounds - inorganic and organic. The inorganic substances of the cell include water, mineral salts, acids, etc., and the organic substances include proteins, nucleic acids, carbohydrates, lipids, ATP, vitamins, etc.

Water(H 2 O) is the most common inorganic substance of the cell, which has unique physicochemical properties. It has no taste, no color, no smell. The density and viscosity of all substances is assessed using water. Like many other substances, water can exist in three states of aggregation: solid (ice), liquid and gaseous (steam). The melting point of water is $0°$С, the boiling point is $100°$С, however, the dissolution of other substances in water can change these characteristics. The heat capacity of water is also quite high - 4200 kJ/mol K, which gives it the opportunity to take part in thermoregulation processes. In a water molecule, the hydrogen atoms are located at an angle of $105°$, while the shared electron pairs are pulled away by the more electronegative oxygen atom. This determines the dipole properties of water molecules (one end is positively charged and the other negatively charged) and the possibility of the formation of hydrogen bonds between water molecules. The cohesion of water molecules underlies the phenomenon of surface tension, capillarity and the properties of water as a universal solvent. As a result, all substances are divided into those soluble in water (hydrophilic) and insoluble in it (hydrophobic). Thanks to these unique properties, it is predetermined that water has become the basis of life on Earth.

Mineral salts may be in dissolved or undissolved states. Soluble salts dissociate into ions - cations and anions. The most important cations are potassium and sodium ions, which facilitate the transfer of substances across the membrane and are involved in the occurrence and conduction of nerve impulses; as well as calcium ions, which takes part in the processes of muscle fiber contraction and blood clotting; magnesium, which is part of chlorophyll; iron, which is part of a number of proteins, including hemoglobin. The most important anions are the phosphate anion, which is part of ATP and nucleic acids, and the carbonic acid residue, which softens fluctuations in the pH of the environment. Ions of mineral salts ensure the penetration of water itself into the cell and its retention in it. If the salt concentration in the environment is lower than in the cell, then water penetrates into the cell. Ions also determine the buffering properties of the cytoplasm, i.e. its ability to maintain a constant slightly alkaline pH of the cytoplasm, despite the constant formation of acidic and alkaline products in the cell.

Insoluble salts(CaCO 3, Ca 3 (PO 4) 2, etc.) are part of the bones, teeth, shells and shells of unicellular and multicellular animals.

In addition, organisms can produce other inorganic compounds, such as acids and oxides. Thus, the parietal cells of the human stomach produce hydrochloric acid, which activates the digestive enzyme pepsin, and silicon oxide permeates the cell walls of horsetails and forms the shells of diatoms. In recent years, the role of nitric oxide (II) in signaling in cells and the body has also been studied.

Organic matter

General characteristics of the organic substances of the cell

The organic substances of a cell can be represented by both relatively simple molecules and more complex ones. In cases where a complex molecule (macromolecule) is formed by a significant number of repeating simpler molecules, it is called polymer, and structural units - monomers. Depending on whether polymer units are repeated or not, they are classified as regular or irregular. Polymers make up up to 90% of the dry matter mass of the cell. They belong to three main classes of organic compounds - carbohydrates (polysaccharides), proteins and nucleic acids. Polysaccharides are regular polymers, while proteins and nucleic acids are irregular. In proteins and nucleic acids, the sequence of monomers is extremely important, since they perform an information function.

Carbohydrates

Carbohydrates- These are organic compounds that consist mainly of three chemical elements - carbon, hydrogen and oxygen, although a number of carbohydrates also contain nitrogen or sulfur. The general formula of carbohydrates is C m (H 2 O) n. They are divided into simple and complex carbohydrates.

Simple carbohydrates (monosaccharides) contain a single sugar molecule that cannot be broken down into simpler ones. These are crystalline substances, sweet in taste and highly soluble in water. Monosaccharides take an active part in cell metabolism and are part of complex carbohydrates - oligosaccharides and polysaccharides.

Monosaccharides are classified according to the number of carbon atoms (C 3 -C 9), for example, pentoses(C 5) and hexoses(C 6). Pentoses include ribose and deoxyribose. Ribose is part of RNA and ATP. Deoxyribose is a component of DNA. Hexoses (C 6 H 12 O 6) are glucose, fructose, galactose, etc. Glucose(grape sugar) is found in all organisms, including human blood, since it is an energy reserve. It is part of many complex sugars: sucrose, lactose, maltose, starch, cellulose, etc. Fructose(fruit sugar) is found in highest concentrations in fruits, honey, and sugar beet roots. It not only takes an active part in metabolic processes, but is also part of sucrose and some polysaccharides, such as insulin.

Most monosaccharides are capable of giving a silver mirror reaction and reducing copper when adding feling liquid (a mixture of solutions of copper (II) sulfate and potassium sodium tartrate) and boiling.

TO oligosaccharides include carbohydrates formed by several monosaccharide residues. They are generally also highly soluble in water and sweet in taste. Depending on the number of these residues, disaccharides (two residues), trisaccharides (three), etc. are distinguished. Disaccharides include sucrose, lactose, maltose, etc. Sucrose(beet or cane sugar) consists of residues of glucose and fructose, it is found in the storage organs of some plants. There is especially a lot of sucrose in the root crops of sugar beets and sugar cane where do they get them from? industrially. It serves as the standard for the sweetness of carbohydrates. Lactose, or milk sugar, formed by glucose and galactose residues, found in maternal and cow's milk. Maltose(malt sugar) consists of two glucose units. It is formed during the breakdown of polysaccharides in plant seeds and in the human digestive system, and is used in the production of beer.

Polysaccharides are biopolymers whose monomers are mono- or disaccharide residues. Most polysaccharides are insoluble in water and have an unsweetened taste. These include starch, glycogen, cellulose and chitin. Starch is a white powdery substance that is not wetted by water, but forms when brewed hot water suspension - paste. In reality, starch consists of two polymers - the less branched amylose and the more branched amylopectin (Fig. 2.9). The monomer of both amylose and amylopectin is glucose. Starch is the main storage substance of plants, which accumulates in huge quantities in seeds, fruits, tubers, rhizomes and other storage organs of plants. A qualitative reaction to starch is a reaction with iodine, in which the starch turns blue-violet.

Glycogen(animal starch) is a reserve polysaccharide of animals and fungi, which in humans is the largest quantities accumulates in muscles and liver. It is also insoluble in water and does not taste sweet. The monomer of glycogen is glucose. Compared to starch molecules, glycogen molecules are even more branched.

Cellulose, or cellulose, is the main supporting polysaccharide of plants. The monomer of cellulose is glucose. Unbranched cellulose molecules form bundles that form part of plant cell walls. Cellulose is the basis of wood, it is used in construction, in the production of textiles, paper, alcohol and many organic substances. Cellulose is chemically inert and does not dissolve in either acids or alkalis. It is also not broken down by enzymes in the human digestive system, but its digestion is facilitated by bacteria in the large intestine. In addition, fiber stimulates contractions of the walls of the gastrointestinal tract, helping to improve its functioning.

Chitin is a polysaccharide whose monomer is a nitrogen-containing monosaccharide. It is part of the cell walls of fungi and arthropod shells. The human digestive system also lacks the enzyme for digesting chitin; only some bacteria have it.

Functions of carbohydrates. Carbohydrates perform plastic (construction), energy, storage and support functions in the cell. They form the cell walls of plants and fungi. The energy value of the breakdown of 1 g of carbohydrates is 17.2 kJ. Glucose, fructose, sucrose, starch and glycogen are storage substances. Carbohydrates can also be part of complex lipids and proteins, forming glycolipids and glycoproteins, particularly in cell membranes. No less important is the role of carbohydrates in intercellular recognition and perception of signals from the external environment, since they function as receptors as part of glycoproteins.

Lipids

Lipids is a chemically heterogeneous group of low molecular weight substances with hydrophobic properties. These substances are insoluble in water and form emulsions in it, but are highly soluble in organic solvents. Lipids are oily to the touch, many of them leave characteristic non-drying marks on paper. Together with proteins and carbohydrates, they are one of the main components of cells. The content of lipids in different cells is not the same, there is especially a lot of it in the seeds and fruits of some plants, in the liver, heart, and blood.

Depending on the structure of the molecule, lipids are divided into simple and complex. TO simple Lipids include neutral lipids (fats), waxes and steroids. Complex lipids also contain another, non-lipid component. The most important of them are phospholipids, glycolipids, etc.

Fats are esters of the trihydric alcohol glycerol and higher fatty acids. Most fatty acids contain 14-22 carbon atoms. Among them there are both saturated and unsaturated, that is, containing double bonds. The most common saturated fatty acids are palmitic and stearic, and the most common unsaturated fatty acids are oleic. Some unsaturated fatty acid are not synthesized in the human body or are synthesized in insufficient quantities, and therefore are irreplaceable. Glycerol residues form hydrophilic “heads”, and fatty acid residues form hydrophobic “tails”.

Fats primarily perform a storage function in cells and serve as a source of energy. Subcutaneous fatty tissue is rich in them, performing shock-absorbing and thermal insulation functions, and in aquatic animals they also increase buoyancy. Plant fats mostly contain unsaturated fatty acids, as a result of which they are liquid and are called oils. Oils are contained in the seeds of many plants, such as sunflower, soybeans, rapeseed, etc.

Waxes- These are esters and mixtures of fatty acids and fatty alcohols. In plants, they form a film on the surface of the leaf, which protects against evaporation, penetration of pathogens, etc. In a number of animals, they cover the body or serve to build honeycombs.

TO steroids These include lipids such as cholesterol, an essential component of cell membranes, as well as sex hormones estradiol, testosterone, vitamin D, etc.

Phospholipids, in addition to glycerol and fatty acid residues, contain an orthophosphoric acid residue. They are part of cell membranes and provide their barrier properties.

Glycolipids are also components of membranes, but their content there is small. The non-lipid part of glycolipids are carbohydrates.

Functions of lipids. Lipids perform plastic (construction), energy, storage, protective, excretory and regulatory functions in the cell; in addition, they are vitamins. It is an essential component of cell membranes. When 1 g of lipids is broken down, 38.9 kJ of energy is released. They are stored in various organs of plants and animals. In addition, subcutaneous fatty tissue protects internal organs from hypothermia or overheating, as well as shock. The regulatory function of lipids is due to the fact that some of them are hormones. The fatty body of insects serves for excretion.

Squirrels

Squirrels- These are high-molecular compounds, biopolymers, the monomers of which are amino acids linked by peptide bonds.

Amino acid called an organic compound having an amino group, a carboxyl group and a radical. In total, about 200 amino acids are found in nature, which differ in radicals and mutual arrangement of functional groups, but only 20 of them can be part of proteins. These amino acids are called proteinogenic.

Unfortunately, not all proteinogenic amino acids can be synthesized in the human body, so they are divided into replaceable and essential. Nonessential amino acids are formed in the human body in the required quantity, and irreplaceable- No. They must be supplied with food, but can also be partially synthesized by intestinal microorganisms. There are 8 completely essential amino acids. These include valine, isoleucine, leucine, lysine, methionine, threonine, tryptophan and phenylalanine. Despite the fact that absolutely all proteinogenic amino acids are synthesized in plants, plant proteins are incomplete because they do not contain a complete set of amino acids, and the presence of protein in the vegetative parts of plants rarely exceeds 1-2% of the mass. Therefore, it is necessary to eat proteins not only of plant origin, but also of animal origin.

A sequence of two amino acids linked by peptide bonds is called dipeptide, out of three - tripeptide etc. Among the peptides there are such important compounds as hormones (oxytocin, vasopressin), antibiotics, etc. A chain of more than twenty amino acids is called polypeptide, and polypeptides containing more than 60 amino acid residues are proteins.

Levels of protein structural organization. Proteins can have primary, secondary, tertiary and quaternary structures.

Primary protein structure- This linear sequence of amino acids connected by a peptide bond. The primary structure ultimately determines the specificity of a protein and its uniqueness, since even if we assume that the average protein contains 500 amino acid residues, then the number of possible combinations is 20,500. Therefore, a change in the location of at least one amino acid in the primary structure entails a change secondary and higher structures, as well as the properties of the protein as a whole.

The structural features of the protein determine its spatial arrangement—the emergence of secondary and tertiary structures.

Secondary structure represents the spatial arrangement of a protein molecule in the form spirals or folds, held by hydrogen bonds between the oxygen and hydrogen atoms of peptide groups of different turns of the helix or folds. Many proteins contain more or less long regions with secondary structure. These are, for example, keratins of hair and nails, silk fibroin.

Tertiary structure squirrel ( globule) is also a form of spatial arrangement of a polypeptide chain held together by hydrophobic, hydrogen, disulfide (S-S) and other bonds. It is characteristic of most proteins in the body, such as muscle myoglobin.

Quaternary structure- the most complex, formed by several polypeptide chains connected mainly by the same bonds as in the tertiary one (hydrophobic, ionic and hydrogen), as well as other weak interactions. Quaternary structure is characteristic of few proteins, such as hemoglobin, chlorophyll, etc.

Based on the shape of the molecule, they are distinguished fibrillar And globular proteins. The first of them are elongated, such as collagen connective tissue or hair and nail keratins. Globular proteins have the shape of a ball (globule), like muscle myoglobin.

Simple and complex proteins. Proteins can be simple And complex. Simple proteins are made up of only amino acids, whereas complex proteins (lipoproteins, chromoproteins, glycoproteins, nucleoproteins, etc.) contain protein and non-protein parts. Chromoproteins contain a colored non-protein part. These include hemoglobin, myoglobin, chlorophyll, cytochromes, etc. Thus, in the composition of hemoglobin, each of the four polypeptide chains of the globin protein is associated with a non-protein part - heme, in the center of which there is an iron ion, which gives hemoglobin a red color. Non-protein part lipoproteins is a lipid, and glycoproteins- carbohydrate. Both lipoproteins and glycoproteins are part of cell membranes. Nucleoproteins are complexes of proteins and nucleic acids (DNA and RNA). They perform essential functions in the processes of storage and transmission of hereditary information.

Properties of proteins. Many proteins are highly soluble in water, but there are also those that dissolve only in solutions of salts, alkalis, acids or organic solvents. The structure of the protein molecule and its functional activity depend on the conditions environment. The loss of its structure by a protein molecule while maintaining its primary structure is called denaturation.

Denaturation occurs due to changes in temperature, pH, atmospheric pressure, under the influence of acids, alkalis, salts heavy metals, organic solvents, etc. The reverse process of restoration of secondary and higher structures is called renaturation, however, it is not always possible. The complete destruction of a protein molecule is called destruction.

Functions of proteins. Proteins perform a number of functions in the cell: plastic (construction), catalytic (enzymatic), energy, signaling (receptor), contractile (motor), transport, protective, regulatory and storage.

The construction function of proteins is associated with their presence in cell membranes and structural components of the cell. Energy - due to the fact that when 1 g of protein is broken down, 17.2 kJ of energy is released. Membrane receptor proteins take an active part in the perception of environmental signals and their transmission throughout the cell, as well as in intercellular recognition. Without proteins, the movement of cells and organisms as a whole is impossible, since they form the basis of flagella and cilia, and also ensure muscle contraction and the movement of intracellular components. In the blood of humans and many animals, the protein hemoglobin carries oxygen and part of the carbon dioxide, other proteins transport ions and electrons. The protective role of proteins is associated primarily with immunity, since the interferon protein is capable of destroying many viruses, and antibody proteins suppress the development of bacteria and other foreign agents. Among proteins and peptides there are many hormones, for example, the pancreatic hormone - insulin, which regulates the concentration of glucose in the blood. In some organisms, proteins can be stored as reserves, like legumes in seeds, or the whites of a chicken egg.

Nucleic acids

Nucleic acids are biopolymers whose monomers are nucleotides. Currently, two types of nucleic acids are known: ribonucleic acid (RNA) and deoxyribonucleic acid (DNA).

Nucleotide formed by a nitrogenous base, a pentose sugar residue and an orthophosphoric acid residue. The characteristics of nucleotides are mainly determined by the nitrogenous bases that make up them, therefore, even conventionally, nucleotides are designated by the first letters of their names. Nucleotides can contain five nitrogenous bases: adenine (A), guanine (G), thymine (T), uracil (U) and cytosine (C). The pentose nucleotides - ribose and deoxyribose - determine which nucleotide will be formed - a ribonucleotide or a deoxyribonucleotide. Ribonucleotides are monomers of RNA, can act as signal molecules (cAMP) and are part of high-energy compounds, such as ATP, and coenzymes, such as NADP, NAD, FAD, etc., and deoxyribonucleotides are part of DNA.

Deoxyribonucleic acid (DNA) is a double-stranded biopolymer whose monomers are deoxyribonucleotides. Deoxyribonucleotides contain only four nitrogenous bases out of five possible - adenine (A), thymine (T), guanine (G) or cytosine (C), as well as deoxyribose and orthophosphoric acid residues. Nucleotides in the DNA chain are connected to each other through orthophosphoric acid residues, forming a phosphodiester bond. When a double-stranded molecule is formed, the nitrogenous bases are directed toward the inside of the molecule. However, the joining of DNA chains does not occur randomly - the nitrogenous bases of different chains are connected to each other by hydrogen bonds according to the principle of complementarity: adenine is connected to thymine by two hydrogen bonds (A=T), and guanine is connected to cytosine by three (G$≡C).

They were installed for her Chargaff's rules:

The number of DNA nucleotides containing adenine is equal to the number of nucleotides containing thymine (A=T).
The number of DNA nucleotides containing guanine is equal to the number of nucleotides containing cytosine (G$≡$C).
The sum of deoxyribonucleotides containing adenine and guanine is equal to the sum of deoxyribonucleotides containing thymine and cytosine (A+G = T+C).
The ratio of the sum of deoxyribonucleotides containing adenine and thymine to the sum of deoxyribonucleotides containing guanine and cytosine depends on the type of organism.

The structure of DNA was deciphered by F. Crick and D. Watson (Nobel Prize in Physiology or Medicine, 1962). According to their model, the DNA molecule is a right-handed double helix. The distance between nucleotides in a DNA chain is 0.34 nm.

The most important property of DNA is the ability to replicate (self-duplicate). The main function of DNA is the storage and transmission of hereditary information, which is written in the form of nucleotide sequences. The stability of the DNA molecule is maintained by powerful repair (recovery) systems, but even they are not able to completely eliminate adverse effects, which ultimately leads to the occurrence of mutations. The DNA of eukaryotic cells is concentrated in the nucleus, mitochondria and plastids, while in prokaryotic cells it is located directly in the cytoplasm. Nuclear DNA is the basis of chromosomes; it is represented by open molecules. The DNA of mitochondria, plastids and prokaryotes is circular.

Ribonucleic acid (RNA)- a biopolymer whose monomers are ribonucleotides. They also contain four nitrogenous bases - adenine (A), uracil (U), guanine (G) or cytosine (C), thereby differing from DNA in one of the bases (instead of thymine, RNA contains uracil). The pentose sugar residue in ribonucleotides is represented by ribose. RNA is mostly single-stranded molecules, with the exception of some viral ones. There are three main types of RNA: messenger or template (mRNA), ribosomal (rRNA) and transport (tRNA). All of them are formed in the process transcriptions- rewriting from DNA molecules.

And RNAs make up the smallest fraction of RNA in a cell (2-4%), which is compensated by their diversity, since one cell can contain thousands of different mRNAs. These are single-chain molecules that are templates for the synthesis of polypeptide chains. Information about the protein structure is recorded in them in the form of nucleotide sequences, with each amino acid encoded by a triplet of nucleotides - codon.

R RNAs are the most abundant type of RNA in a cell (up to 80%). Their molecular mass averages 3000-5000; are formed in the nucleoli and are part of cellular organelles - ribosomes. rRNAs also appear to play a role in protein synthesis.

T RNA is the smallest of the RNA molecules, as it contains only 73-85 nucleotides. Their share of the total amount of RNA in the cell is about 16%. The function of tRNA is to transport amino acids to the site of protein synthesis (ribosomes). The tRNA molecule is shaped like a clover leaf. At one end of the molecule there is a site for the attachment of an amino acid, and in one of the loops there is a triplet of nucleotides, complementary to the mRNA codon and determining which amino acid the tRNA will carry - anticodon.

All types of RNA take an active part in the process of implementing hereditary information, which is transcribed from DNA to mRNA, and the latter carries out protein synthesis. tRNA delivers amino acids to ribosomes during protein synthesis, and rRNA is part of the ribosomes themselves.

Adenosine triphosphoric acid (ATP) is a nucleotide containing, in addition to the nitrogenous base adenine and a ribose residue, three phosphoric acid residues. The bonds between the last two phosphorus residues are high-energy (cleavage releases 42 kJ/mol of energy), while the standard chemical bond during cleavage produces 12 kJ/mol. When energy is needed, the macroergic bond of ATP is cleaved, adenosine diphosphoric acid (ADP), a phosphorus residue is formed, and energy is released:

ATP + H 2 O $→$ ADP + H 3 PO 4 + 42 kJ.

ADP can also be broken down to form AMP (adenosine monophosphoric acid) and a phosphoric acid residue:

ADP + H 2 O $→$ AMP + H 3 PO 4 + 42 kJ.

In progress energy metabolism(during respiration, fermentation), as well as during photosynthesis, ADP attaches a phosphorus residue and turns into ATP. The ATP reduction reaction is called phosphorylation. ATP is a universal source of energy for all life processes of living organisms.

The study of the chemical composition of the cells of all living organisms has shown that they contain the same chemical elements, chemical substances that perform the same functions. Moreover, a section of DNA transferred from one organism to another will work in it, and a protein synthesized by bacteria or fungi will perform the functions of a hormone or enzyme in the human body. This is one of the proofs of the unity of origin of the organic world.

Cell structure. The relationship between the structure and functions of the parts and organelles of a cell is the basis of its integrity

Cell structure

Structure of prokaryotic and eukaryotic cells

The main structural components of cells are the plasma membrane, cytoplasm and hereditary apparatus. Depending on the characteristics of the organization, two main types of cells are distinguished: prokaryotic and eukaryotic. The main difference between prokaryotic cells and eukaryotic cells is the organization of their hereditary apparatus: in prokaryotes it is located directly in the cytoplasm (this area of the cytoplasm is called nucleoid) and is not separated from it by membrane structures, whereas in eukaryotes most of the DNA is concentrated in the nucleus, surrounded by a double membrane. In addition, the genetic information of prokaryotic cells, located in the nucleoid, is written in a circular DNA molecule, while in eukaryotes the DNA molecules are open.

Unlike eukaryotes, the cytoplasm of prokaryotic cells also contains a small number of organelles, while eukaryotic cells are characterized by a significant variety of these structures.

Structure and functions of biological membranes

The structure of the biomembrane. The cell-bounding membranes and membrane organelles of eukaryotic cells have a common chemical composition and structure. They include lipids, proteins and carbohydrates. Membrane lipids are mainly represented by phospholipids and cholesterol. Most membrane proteins are complex proteins, such as glycoproteins. Carbohydrates do not occur independently in the membrane; they are associated with proteins and lipids. The thickness of the membranes is 7-10 nm.

According to the currently generally accepted fluid mosaic model of membrane structure, lipids form a double layer, or lipid bilayer, in which the hydrophilic “heads” of lipid molecules face outward, and the hydrophobic “tails” are hidden inside the membrane. These “tails,” due to their hydrophobicity, ensure the separation of the aqueous phases of the internal environment of the cell and its environment. With lipids using various types interactions are related proteins. Some proteins are located on the surface of the membrane. Such proteins are called peripheral, or superficial. Other proteins are partially or completely immersed in the membrane - these are integral, or submerged proteins. Membrane proteins perform structural, transport, catalytic, receptor and other functions.

Membranes are not like crystals; their components are constantly in motion, as a result of which gaps appear between lipid molecules - pores through which various substances can enter or leave the cell.

Biological membranes differ in their location in the cell, chemical composition and functions. The main types of membranes are plasma and internal. Plasma membrane contains about 45% lipids (including glycolipids), 50% proteins and 5% carbohydrates. Chains of carbohydrates, which are part of complex proteins-glycoproteins and complex lipids-glycolipids, protrude above the surface of the membrane. Plasmalemma glycoproteins are extremely specific. For example, they are used for mutual recognition of cells, including sperm and egg.

On the surface of animal cells, carbohydrate chains form a thin surface layer - glycocalyx. It is detected in almost all animal cells, but its degree of expression varies (10-50 µm). The glycocalyx provides direct communication between the cell and the external environment, where extracellular digestion occurs; Receptors are located in the glycocalyx. In addition to the plasmalemma, the cells of bacteria, plants and fungi are also surrounded by cell membranes.

Internal membranes eukaryotic cells delimit different parts of the cell, forming peculiar “compartments” - compartments, which promotes the separation of various metabolic and energy processes. They may differ in chemical composition and functions, but their general structural plan remains the same.

Membrane functions:

Limiting. The idea is that they separate the internal space of the cell from the external environment. The membrane is semi-permeable, that is, only those substances that the cell needs can freely pass through it, and there are mechanisms for transporting the necessary substances.
Receptor. It is primarily associated with the perception of environmental signals and the transfer of this information into the cell. Special receptor proteins are responsible for this function. Membrane proteins are also responsible for cellular recognition according to the “friend or foe” principle, as well as for the formation of intercellular connections, the most studied of which are the synapses of nerve cells.
Catalytic. Numerous enzyme complexes are located on the membranes, as a result of which intensive synthetic processes occur on them.
Energy transforming. Associated with the formation of energy, its storage in the form of ATP and consumption.
Compartmentalization. Membranes also delimit the space inside the cell, thereby separating the starting materials of the reaction and the enzymes that can carry out the corresponding reactions.
Formation of intercellular contacts. Despite the fact that the thickness of the membrane is so small that it cannot be distinguished with the naked eye, it, on the one hand, serves as a fairly reliable barrier for ions and molecules, especially water-soluble ones, and on the other, ensures their transport into and out of the cell.
Transport.

Membrane transport. Due to the fact that cells, as elementary biological systems, are open systems, to ensure metabolism and energy, maintain homeostasis, growth, irritability and other processes, the transfer of substances through the membrane - membrane transport - is required. Currently, the transport of substances across the cell membrane is divided into active, passive, endo- and exocytosis.

Passive transport- This is a type of transport that occurs without energy consumption from higher to lower concentrations. Lipid-soluble small non-polar molecules (O 2, CO 2) easily penetrate the cell by simple diffusion. Those insoluble in lipids, including charged small particles, are picked up by carrier proteins or pass through special channels (glucose, amino acids, K +, PO 4 3-). This type of passive transport is called facilitated diffusion. Water enters the cell through pores in the lipid phase, as well as through special channels lined with proteins. The transport of water through a membrane is called by osmosis.

Osmosis is extremely important in the life of a cell, because if it is placed in a solution with a higher concentration of salts than in the cell solution, then water will begin to leave the cell and the volume of living contents will begin to decrease. In animal cells, the cell as a whole shrinks, and in plant cells, the cytoplasm lags behind the cell wall, which is called plasmolysis. When a cell is placed in a solution less concentrated than the cytoplasm, water transport occurs in the opposite direction - into the cell. However, there are limits to the extensibility of the cytoplasmic membrane, and an animal cell eventually ruptures, while a plant cell does not allow this to happen due to its strong cell wall. The phenomenon of filling the entire internal space of a cell with cellular contents is called deplasmolysis. The intracellular concentration of salts should be taken into account when preparing medications, especially for intravenous administration, as this can lead to damage to blood cells (for this, saline solution with a concentration of 0.9% sodium chloride is used). This is no less important when cultivating cells and tissues, as well as animal and plant organs.

Active transport proceeds with the expenditure of ATP energy from a lower concentration of a substance to a higher one. It is carried out using special pump proteins. Proteins pump K + , Na + , Ca 2+ and other ions through the membrane, which promotes the transport of essential organic substances, as well as the emergence of nerve impulses, etc.

Endocytosis- this is an active process of absorption of substances by the cell, in which the membrane forms invaginations and then forms membrane vesicles - phagosomes, which contain the absorbed objects. Then the primary lysosome fuses with the phagosome and forms secondary lysosome, or phagolysosome, or digestive vacuole. The contents of the vesicle are digested by lysosome enzymes, and the breakdown products are absorbed and assimilated by the cell. Undigested residues are removed from the cell by exocytosis. There are two main types of endocytosis: phagocytosis and pinocytosis.

Phagocytosis is the process of capture by the cell surface and absorption of solid particles by the cell, and pinocytosis- liquids. Phagocytosis occurs mainly in animal cells (single-celled animals, human leukocytes), it provides their nutrition and often protects the body. By pinocytosis, proteins, antigen-antibody complexes are absorbed during immune reactions, etc. However, many viruses also enter the cell by pinocytosis or phagocytosis. In plant and fungal cells, phagocytosis is practically impossible, since they are surrounded by durable cell membranes.

Exocytosis- a process reverse to endocytosis. In this way, undigested food remains are released from the digestive vacuoles, and substances necessary for the life of the cell and the body as a whole are removed. For example, the transmission of nerve impulses occurs due to the release of chemical messengers by the neuron sending the impulse - mediators, and in plant cells this is how auxiliary carbohydrates of the cell membrane are secreted.

Cell walls of plant cells, fungi and bacteria. Outside the membrane, the cell can secrete a strong framework - cell membrane, or cell wall.

In plants, the basis of the cell wall is cellulose, packed in bundles of 50-100 molecules. The spaces between them are filled with water and other carbohydrates. The plant cell wall is permeated with tubules - plasmodesmata, through which the membranes of the endoplasmic reticulum pass. Plasmodesmata carry out the transport of substances between cells. However, transport of substances, such as water, can also occur along the cell walls themselves. Over time, various substances, including tannins or fat-like substances, accumulate in the cell wall of plants, which leads to lignification or suberization of the cell wall itself, displacement of water and death of cellular contents. Between the cell walls of neighboring plant cells there are jelly-like spacers - middle plates that hold them together and cement the plant body as a whole. They are destroyed only during the process of fruit ripening and when the leaves fall.

The cell walls of fungal cells are formed chitin- a carbohydrate containing nitrogen. They are quite strong and are the external skeleton of the cell, but still, like in plants, they prevent phagocytosis.

In bacteria, the cell wall contains carbohydrates with peptide fragments - murein, however, its content varies significantly among different groups bacteria. Other polysaccharides can also be secreted on top of the cell wall, forming a mucous capsule that protects bacteria from external influences.

The membrane determines the shape of the cell, serves as a mechanical support, performs a protective function, provides the osmotic properties of the cell, limiting the stretching of the living contents and preventing rupture of the cell, which increases due to the entry of water. In addition, water and substances dissolved in it overcome the cell wall before entering the cytoplasm or, conversely, when leaving it, while water is transported through the cell walls faster than through the cytoplasm.

Cytoplasm

Cytoplasm- This is the internal contents of the cell. All cell organelles, the nucleus and various waste products are immersed in it.

The cytoplasm connects all parts of the cell to each other, and numerous metabolic reactions take place in it. The cytoplasm is separated from the environment and divided into compartments by membranes, that is, cells have a membrane structure. It can be in two states - sol and gel. Sol- this is a semi-liquid, jelly-like state of the cytoplasm, in which vital processes proceed most intensively, and gel- a denser, gelatinous state that impedes the occurrence of chemical reactions and the transport of substances.

The liquid part of the cytoplasm without organelles is called hyaloplasm. Hyaloplasm, or cytosol, is a colloidal solution in which there is a kind of suspension of fairly large particles, for example proteins, surrounded by dipoles of water molecules. Precipitation of this suspension does not occur due to the fact that they have the same charge and repel each other.

Organoids

Organoids- These are permanent components of the cell that perform specific functions.

Depending on their structural features, they are divided into membrane and non-membrane. Membrane organelles, in turn, are classified as single-membrane (endoplasmic reticulum, Golgi complex and lysosomes) or double-membrane (mitochondria, plastids and nucleus). Non-membrane The organelles are ribosomes, microtubules, microfilaments and the cell center. Of the listed organelles, only ribosomes are inherent in prokaryotes.

Structure and functions of the nucleus. Core- a large double-membrane organelle lying in the center of the cell or at its periphery. The dimensions of the nucleus can range from 3-35 microns. The shape of the nucleus is most often spherical or ellipsoidal, but there are also rod-shaped, fusiform, bean-shaped, lobed and even segmented nuclei. Some researchers believe that the shape of the nucleus corresponds to the shape of the cell itself.

Most cells have one nucleus, but, for example, in the cells of the liver and heart there can be two of them, and in a number of neurons - up to 15. Skeletal muscle fibers usually contain many nuclei, but they are not cells in the full sense of the word, since they are formed in the result of the fusion of several cells.

The core is surrounded nuclear envelope, and its internal space is filled nuclear juice, or nucleoplasm (karyoplasm), in which they are immersed chromatin And nucleolus. The nucleus performs such important functions as storing and transmitting hereditary information, as well as controlling the life of the cell.

The role of the nucleus in the transmission of hereditary information was convincingly proven in experiments with the green alga Acetabularia. In a single giant cell, reaching a length of 5 cm, a cap, a stalk and a rhizoid are distinguished. Moreover, it contains only one nucleus located in the rhizoid. In the 1930s, I. Hemmerling transplanted the nucleus of one species of acetabularia with a green color into the rhizoid of another species, with a brown color, from which the nucleus had been removed. After some time, the plant with the transplanted nucleus grew a new cap, like the nucleus donor algae. At the same time, the cap or stalk, separated from the rhizoid and not containing a nucleus, died after some time.

Nuclear envelope formed by two membranes - outer and inner, between which there is space. The intermembrane space communicates with the cavity of the rough endoplasmic reticulum, and the outer membrane of the nucleus can carry ribosomes. The nuclear envelope is permeated with numerous pores lined with special proteins. Transport of substances occurs through the pores: the necessary proteins (including enzymes), ions, nucleotides and other substances enter the nucleus, and RNA molecules, spent proteins, and subunits of ribosomes leave it. Thus, the functions of the nuclear envelope are the separation of the contents of the nucleus from the cytoplasm, as well as the regulation of metabolism between the nucleus and the cytoplasm.

Nucleoplasm called the contents of the nucleus, in which chromatin and the nucleolus are immersed. It is a colloidal solution, chemically reminiscent of cytoplasm. Enzymes of the nucleoplasm catalyze the exchange of amino acids, nucleotides, proteins, etc. The nucleoplasm is connected to the hyaloplasm through nuclear pores. The functions of the nucleoplasm, like the hyaloplasm, are to ensure the interconnection of all structural components of the nucleus and to carry out a number of enzymatic reactions.

Chromatin called a collection of thin filaments and granules immersed in the nucleoplasm. It can only be detected by staining, since the refractive indices of chromatin and nucleoplasm are approximately the same. The filamentous component of chromatin is called euchromatin, and granular - heterochromatin. Euchromatin is weakly compacted, since hereditary information is read from it, while more spiralized heterochromatin is genetically inactive.

Chromatin is a structural modification of chromosomes in a non-dividing nucleus. Thus, chromosomes are constantly present in the nucleus; only their state changes depending on the function that the nucleus performs at the moment.

The composition of chromatin mainly includes nucleoprotein proteins (deoxyribonucleoproteins and ribonucleoproteins), as well as enzymes, the most important of which are associated with the synthesis of nucleic acids, and some other substances.

The functions of chromatin consist, firstly, in the synthesis of nucleic acids specific to a given organism, which direct the synthesis of specific proteins, and secondly, in the transfer of hereditary properties from the mother cell to the daughter cells, for which purpose the chromatin threads are packaged into chromosomes during the division process.

Nucleolus- a spherical body, clearly visible under a microscope, with a diameter of 1-3 microns. It is formed on sections of chromatin in which information about the structure of rRNA and ribosomal proteins is encoded. There is often only one nucleolus in the nucleus, but in those cells where intensive vital processes occur, there may be two or more nucleoli. The functions of the nucleoli are the synthesis of rRNA and the assembly of ribosomal subunits by combining rRNA with proteins coming from the cytoplasm.

Mitochondria- double-membrane organelles of round, oval or rod-shaped form, although spiral-shaped ones are also found (in sperm). The diameter of mitochondria is up to 1 µm, and the length is up to 7 µm. The space inside the mitochondria is filled with matrix. Matrix- This is the main substance of mitochondria. A circular DNA molecule and ribosomes are immersed in it. The outer membrane of mitochondria is smooth and impermeable to many substances. The inner membrane has projections - cristas, increasing the surface area of membranes for chemical reactions to occur. On the surface of the membrane there are numerous protein complexes, making up the so-called respiratory chain, as well as mushroom-shaped ATP synthetase enzymes. The aerobic stage of respiration occurs in mitochondria, during which ATP is synthesized.

Plastids- large double-membrane organelles, characteristic only of plant cells. The internal space of the plastids is filled stroma, or matrix. The stroma contains a more or less developed system of membrane vesicles - thylakoids, which are collected in piles - grains, as well as its own circular DNA molecule and ribosomes. There are four main types of plastids: chloroplasts, chromoplasts, leucoplasts and proplastids.

Chloroplasts- these are green plastids with a diameter of 3-10 microns, clearly visible under a microscope. They are found only in the green parts of plants - leaves, young stems, flowers and fruits. Chloroplasts are generally oval or ellipsoidal in shape, but can also be cup-shaped, spiral-shaped, or even lobed. The number of chloroplasts in a cell averages from 10 to 100 pieces. However, for example, in some algae it may be one, have significant dimensions and a complex shape - then it is called chromatophore. In other cases, the number of chloroplasts can reach several hundred, while their sizes are small. The color of chloroplasts is due to the main pigment of photosynthesis - chlorophyll, although they also contain additional pigments - carotenoids. Carotenoids only become noticeable in the fall, when the chlorophyll in aging leaves breaks down. The main function of chloroplasts is photosynthesis. Light reactions of photosynthesis occur on thylakoid membranes, on which chlorophyll molecules are attached, and dark reactions take place in the stroma, where numerous enzymes are contained.

Chromoplasts- These are yellow, orange and red plastids containing carotenoid pigments. The shape of chromoplasts can also vary significantly: they can be tubular, spherical, crystalline, etc. Chromoplasts give color to the flowers and fruits of plants, attracting pollinators and distributors of seeds and fruits.

Leukoplasts- These are white or colorless plastids, mostly round or oval in shape. They are common in non-photosynthetic parts of plants, for example in the skin of leaves, potato tubers, etc. They store nutrients, most often starch, but in some plants it can be proteins or oil.

Plastids are formed in plant cells from proplastids, which are already present in the cells of educational tissue and are small double-membrane bodies. At the early stages of development, different types of plastids are capable of transforming into each other: when exposed to light, the leucoplasts of a potato tuber and the chromoplasts of a carrot root turn green.

Plastids and mitochondria are called semi-autonomous organelles of the cell, since they have their own DNA molecules and ribosomes, carry out protein synthesis and divide independently of cell division. These features are explained by their origin from single-celled prokaryotic organisms. However, the “independence” of mitochondria and plastids is limited, since their DNA contains too few genes for free existence, while the rest of the information is encoded in the chromosomes of the nucleus, which allows it to control these organelles.

Endoplasmic reticulum (ER), or endoplasmic reticulum (ER), is a single-membrane organelle, which is a network of membrane cavities and tubules occupying up to 30% of the contents of the cytoplasm. The diameter of the EPS tubules is about 25-30 nm. There are two types of EPS - rough and smooth. Rough XPS carries ribosomes, where protein synthesis occurs. Smooth XPS lacks ribosomes. Its function is the synthesis of lipids and carbohydrates, as well as the transport, storage and neutralization of toxic substances. It is especially developed in those cells where intensive metabolic processes occur, for example in liver cells - hepatocytes - and skeletal muscle fibers. Substances synthesized in the ER are transported to the Golgi apparatus. The assembly of cell membranes also occurs in the ER, but their formation is completed in the Golgi apparatus.

Golgi apparatus, or Golgi complex, is a single-membrane organelle formed by a system of flat cisterns, tubules and vesicles detached from them. The structural unit of the Golgi apparatus is dictyosome- a stack of tanks, at one pole of which substances from the EPS come, and from the opposite pole, having undergone certain transformations, they are packed into vesicles and sent to other parts of the cell. The diameter of the tanks is about 2 microns, and the diameter of small bubbles is about 20-30 microns. The main functions of the Golgi complex are the synthesis of certain substances and modification (change) of proteins, lipids and carbohydrates coming from the ER, the final formation of membranes, as well as the transport of substances throughout the cell, renewal of its structures and the formation of lysosomes. The Golgi apparatus received its name in honor of the Italian scientist Camillo Golgi, who first discovered this organelle (1898).

Lysosomes- small single-membrane organelles up to 1 μm in diameter, which contain hydrolytic enzymes involved in intracellular digestion. The membranes of lysosomes are poorly permeable to these enzymes, so the lysosomes perform their functions very accurately and targetedly. Thus, they take an active part in the process of phagocytosis, forming digestive vacuoles, and in case of starvation or damage to certain parts of the cell, they digest them without affecting others. The role of lysosomes in cell death processes has recently been discovered.

Vacuole is a cavity in the cytoplasm of plant and animal cells, bounded by a membrane and filled with liquid. Digestive and contractile vacuoles are found in protozoan cells. The former take part in the process of phagocytosis, as they break down nutrients. The latter provide maintenance water-salt balance due to osmoregulation. In multicellular animals, digestive vacuoles are mainly found.

In plant cells, vacuoles are always present; they are surrounded by a special membrane and filled with cell sap. The membrane surrounding the vacuole is similar in chemical composition, structure and functions to the plasma membrane. Cell sap is an aqueous solution of various inorganic and organic substances, including mineral salts, organic acids, carbohydrates, proteins, glycosides, alkaloids, etc. The vacuole can occupy up to 90% of the cell volume and push the nucleus to the periphery. This part of the cell performs storage, excretory, osmotic, protective, lysosomal and other functions, since it accumulates nutrients and waste products, ensures the supply of water and maintains the shape and volume of the cell, and also contains enzymes for the breakdown of many cell components. In addition, the biologically active substances of the vacuoles can prevent many animals from eating these plants. In a number of plants, due to the swelling of vacuoles, cell growth occurs by elongation.

Vacuoles are also present in the cells of some fungi and bacteria, but in fungi they perform only the function of osmoregulation, while in cyanobacteria they maintain buoyancy and participate in the process of assimilation of nitrogen from the air.

Ribosomes- small non-membrane organelles with a diameter of 15-20 microns, consisting of two subunits - large and small. Eukaryotic ribosomal subunits are assembled in the nucleolus and then transported into the cytoplasm. Ribosomes in prokaryotes, mitochondria, and plastids are smaller in size than ribosomes in eukaryotes. Ribosomal subunits include rRNA and proteins.

The number of ribosomes in a cell can reach several tens of millions: in the cytoplasm, mitochondria and plastids they are in a free state, and on the rough ER - in a bound state. They take part in protein synthesis, in particular, they carry out the process of translation - the biosynthesis of a polypeptide chain on an mRNA molecule. Free ribosomes synthesize the proteins of hyaloplasm, mitochondria, plastids, and their own ribosomal proteins, while ribosomes attached to the rough ER carry out the translation of proteins for removal from cells, membrane assembly, and the formation of lysosomes and vacuoles.

Ribosomes can be found singly in the hyaloplasm or assembled in groups during the simultaneous synthesis of several polypeptide chains on one mRNA. Such groups of ribosomes are called polyribosomes, or polysomes.

Microtubules- These are cylindrical hollow non-membrane organelles that penetrate the entire cytoplasm of the cell. Their diameter is about 25 nm, wall thickness is 6-8 nm. They are formed by numerous protein molecules tubulin, which first form 13 threads resembling beads and then assemble into a microtubule. Microtubules form a cytoplasmic reticulum, which gives the cell shape and volume, connects the plasma membrane with other parts of the cell, ensures the transport of substances throughout the cell, takes part in the movement of the cell and intracellular components, as well as in the division of genetic material. They are part of the cell center and organelles of movement - flagella and cilia.

Microfilaments, or microthreads, are also non-membrane organelles, however, they have a filamentous shape and are formed not by tubulin, but actin. They take part in the processes of membrane transport, intercellular recognition, division of the cell cytoplasm and in its movement. In muscle cells, the interaction of actin microfilaments with myosin filaments mediates contraction.

Microtubules and microfilaments form internal skeleton cells - cytoskeleton. It is a complex network of fibers that provide mechanical support for the plasma membrane, determines the shape of the cell, the location of cellular organelles and their movement during cell division.

Cell center- a non-membrane organelle located in animal cells near the nucleus; it is absent in plant cells. Its length is about 0.2-0.3 microns, and its diameter is 0.1-0.15 microns. The cell center is formed by two centrioles, lying in mutually perpendicular planes, and radiant sphere from microtubules. Each centriole is formed by nine groups of microtubules, collected in groups of three, i.e., triplets. The cellular center takes part in the processes of microtubule assembly, division of the cell's hereditary material, as well as in the formation of flagella and cilia.

Organelles of movement. Flagella And cilia They are cell outgrowths covered with plasmalemma. The basis of these organelles is made up of nine pairs of microtubules located along the periphery and two free microtubules in the center. Microtubules are interconnected by various proteins, ensuring their coordinated deviation from the axis - oscillation. Oscillations are energy-dependent, that is, the energy of high-energy ATP bonds is spent on this process. Restoration of lost flagella and cilia is a function basal bodies, or kinetosomes located at their base.

The length of cilia is about 10-15 nm, and the length of flagella is 20-50 µm. Due to strictly directed movements of flagella and cilia, not only the movement of single-celled animals, sperm, etc. occurs, but also the cleaning of the respiratory tract and the movement of the egg through the fallopian tubes, since all these parts of the human body are lined with ciliated epithelium.

Inclusions

Inclusions- These are non-permanent components of the cell that are formed and disappear during its life. These include both reserve substances, for example, grains of starch or protein in plant cells, glycogen granules in the cells of animals and fungi, volutin in bacteria, drops of fat in all types of cells, and waste products, in particular, food residues undigested as a result of phagocytosis , forming so-called residual bodies.

The relationship between the structure and functions of the parts and organelles of a cell is the basis of its integrity

Each of the parts of the cell, on the one hand, is a separate structure with a specific structure and functions, and on the other, a component of a more complex system called a cell. Most of the hereditary information of a eukaryotic cell is concentrated in the nucleus, but the nucleus itself is not able to ensure its implementation, since this requires at least the cytoplasm, which acts as the main substance, and ribosomes, on which this synthesis occurs. Most ribosomes are located on the granular endoplasmic reticulum, from where proteins are most often transported to the Golgi complex, and then, after modification, to those parts of the cell for which they are intended, or are excreted. Membrane packaging of proteins and carbohydrates can be embedded in the membranes of organelles and the cytoplasmic membrane, ensuring their constant renewal. Lysosomes and vacuoles, which perform important functions, also detach from the Golgi complex. For example, without lysosomes, cells would quickly turn into a kind of dumping ground for waste molecules and structures.

The occurrence of all these processes requires energy produced by mitochondria, and in plants, by chloroplasts. And although these organelles are relatively autonomous, since they have their own DNA molecules, some of their proteins are still encoded by the nuclear genome and synthesized in the cytoplasm.

Thus, the cell is an inextricable unity of its constituent components, each of which performs its own unique function.

Metabolism and energy conversion are properties of living organisms. Energy and plastic metabolism, their relationship. Stages of energy metabolism. Fermentation and respiration. Photosynthesis, its significance, cosmic role. Phases of photosynthesis. Light and dark reactions of photosynthesis, their relationship. Chemosynthesis. The role of chemosynthetic bacteria on Earth

Metabolism and energy conversion - properties of living organisms

A cell can be likened to a miniature chemical factory in which hundreds and thousands of chemical reactions occur.

Metabolism- a set of chemical transformations aimed at the preservation and self-reproduction of biological systems.

It includes the intake of substances into the body during nutrition and respiration, intracellular metabolism, or metabolism, as well as the isolation of final metabolic products.

Metabolism is inextricably linked with the processes of converting one type of energy into another. For example, during the process of photosynthesis, light energy is stored in the form of the energy of chemical bonds of complex organic molecules, and during the process of respiration it is released and spent on the synthesis of new molecules, mechanical and osmotic work, dissipated in the form of heat, etc.

The occurrence of chemical reactions in living organisms is ensured thanks to biological catalysts of a protein nature - enzymes, or enzymes. Like other catalysts, enzymes accelerate the occurrence of chemical reactions in a cell by tens and hundreds of thousands of times, and sometimes even make them possible, but do not change the nature or properties of the final product(s) of the reaction and do not change themselves. Enzymes can be both simple and complex proteins, which, in addition to the protein part, also include a non-protein part - cofactor (coenzyme). Examples of enzymes are salivary amylase, which breaks down polysaccharides during prolonged chewing, and pepsin, which ensures the digestion of proteins in the stomach.

Enzymes differ from non-protein catalysts in their high specificity of action, a significant increase in the reaction rate with their help, as well as the ability to regulate the action by changing the conditions of the reaction or the interaction of various substances with them. In addition, the conditions under which enzymatic catalysis occurs differ significantly from those under which non-enzymatic catalysis occurs: the optimal temperature for the functioning of enzymes in the human body is $37°C$, the pressure should be close to atmospheric, and the $pH$ of the environment can significantly hesitate. Thus, amylase requires an alkaline environment, and pepsin requires an acidic environment.

The mechanism of action of enzymes is to reduce the activation energy of substances (substrates) that enter into a reaction due to the formation of intermediate enzyme-substrate complexes.

Energy and plastic metabolism, their relationship

Metabolism consists of two processes occurring simultaneously in the cell: plastic and energy metabolism.

Plastic metabolism (anabolism, assimilation) is a set of synthesis reactions that involve the expenditure of ATP energy. In the process of plastic metabolism, organic substances are synthesized, necessary cage. Examples of plastic exchange reactions are photosynthesis, protein biosynthesis, and DNA replication (self-duplication).

Energy metabolism (catabolism, dissimilation) is a set of cleavage reactions complex substances to more simple ones. As a result of energy metabolism, energy is released and stored in the form of ATP. The most important processes of energy metabolism are respiration and fermentation.

Plastic and energy exchanges are inextricably linked, since in the process of plastic exchange organic substances are synthesized and this requires ATP energy, and in the process of energy exchange organic substances are broken down and energy is released, which will then be spent on synthesis processes.

Organisms receive energy during the process of nutrition, and release it and convert it into an accessible form mainly during the process of respiration. According to the method of nutrition, all organisms are divided into autotrophs and heterotrophs. Autotrophs capable of independently synthesizing organic substances from inorganic ones, and heterotrophs use exclusively prepared organic substances.

Stages of energy metabolism

Despite the complexity of energy metabolism reactions, it is conventionally divided into three stages: preparatory, anaerobic (oxygen-free) and aerobic (oxygen).

On preparatory stage molecules of polysaccharides, lipids, proteins, nucleic acids break down into simpler ones, for example, glucose, glycerol and fatty acids, amino acids, nucleotides, etc. This stage can occur directly in the cells or in the intestines, from where the broken down substances are delivered through the bloodstream.

Anaerobic stage energy metabolism is accompanied by further breakdown of monomers of organic compounds into even simpler intermediate products, for example, pyruvic acid, or pyruvate. It does not require the presence of oxygen, and for many organisms living in the mud of swamps or in the human intestines, it is the only way to obtain energy. The anaerobic stage of energy metabolism occurs in the cytoplasm.

Various substances can undergo oxygen-free cleavage, but quite often the substrate of the reactions is glucose. The process of its oxygen-free splitting is called glycolysis. During glycolysis, a glucose molecule loses four hydrogen atoms, i.e., it is oxidized, and two molecules of pyruvic acid, two molecules of ATP and two molecules of the reduced hydrogen carrier $NADH + H^(+)$ are formed:

$C_6H_(12)O_6 + 2H_3PO_4 + 2ADP + 2NAD → 2C_3H_4O_3 + 2ATP + 2NADH + H^(+) + 2H_2O$.

The formation of ATP from ADP occurs due to the direct transfer of phosphate anion from pre-phosphorylated sugar and is called substrate phosphorylation.

Aerobic stage energy exchange can occur only in the presence of oxygen, while intermediate compounds formed during oxygen-free cleavage are oxidized to the final products (carbon dioxide and water) and most of the energy stored in the chemical bonds of organic compounds is released. It turns into the energy of high-energy bonds of 36 ATP molecules. This stage is also called tissue respiration. In the absence of oxygen, intermediate compounds are converted into other organic substances, a process called fermentation.

Breath

The mechanism of cellular respiration is schematically depicted in Fig.

Aerobic respiration occurs in mitochondria, with pyruvic acid first losing one carbon atom, which is accompanied by the synthesis of one reducing equivalent of $NADH + H^(+)$ and a molecule of acetyl coenzyme A (acetyl-CoA):

$C_3H_4O_3 + NAD + H~CoA → CH_3CO~CoA + NADH + H^(+) + CO_2$.

Acetyl-CoA in the mitochondrial matrix is involved in a chain of chemical reactions, the totality of which is called Krebs cycle (tricarboxylic acid cycle, citric acid cycle). During these transformations, two ATP molecules are formed, acetyl-CoA is completely oxidized to carbon dioxide, and its hydrogen ions and electrons are added to the hydrogen carriers $NADH + H^(+)$ and $FADH_2$. The carriers transport hydrogen protons and electrons to the inner membranes of mitochondria, forming cristae. With the help of carrier proteins, hydrogen protons are pumped into the intermembrane space, and electrons are transmitted through the so-called respiratory chain of enzymes located on the inner membrane of mitochondria and discharged onto oxygen atoms:

$O_2+2e^(-)→O_2^-$.

It should be noted that some respiratory chain proteins contain iron and sulfur.

From the intermembrane space, hydrogen protons are transported back into the mitochondrial matrix with the help of special enzymes - ATP synthases, and the energy released in this case is spent on the synthesis of 34 ATP molecules from each glucose molecule. This process is called oxidative phosphorylation. In the mitochondrial matrix, hydrogen protons react with oxygen radicals to form water:

$4H^(+)+O_2^-→2H_2O$.

The set of reactions of oxygen respiration can be expressed as follows:

$2C_3H_4O_3 + 6O_2 + 36H_3PO_4 + 36ADP → 6CO_2 + 38H_2O + 36ATP.$

The overall breathing equation looks like this:

$C_6H_(12)O_6 + 6O_2 + 38H_3PO_4 + 38ADP → 6CO_2 + 40H_2O + 38ATP.$

Fermentation

In the absence of oxygen or its deficiency, fermentation occurs. Fermentation is an evolutionarily earlier method of obtaining energy than respiration, but it is energetically less beneficial because fermentation produces organic substances that are still rich in energy. There are several main types of fermentation: lactic acid, alcoholic, acetic acid, etc. Thus, in skeletal muscles in the absence of oxygen during fermentation, pyruvic acid is reduced to lactic acid, while the previously formed reducing equivalents are consumed, and only two ATP molecules remain:

$2C_3H_4O_3 + 2NADH + H^(+) → 2C_3H_6O_3 + 2NAD$.

During fermentation with the help of yeast, pyruvic acid in the presence of oxygen is converted into ethyl alcohol and carbon monoxide (IV):

$C_3H_4O_3 + NADH + H^(+) → C_2H_5OH + CO_2 + NAD^(+)$.

During fermentation with the help of microorganisms, acetic, butyric, formic acids, etc. can also be formed from pyruvic acid.

ATP, obtained as a result of energy metabolism, is spent in the cell for various types of work: chemical, osmotic, electrical, mechanical and regulatory. Chemical work involves the biosynthesis of proteins, lipids, carbohydrates, nucleic acids and other vital compounds. Osmotic work includes the processes of absorption by the cell and removal from it of substances that are in the extracellular space in concentrations greater than in the cell itself. Electrical work is closely interrelated with osmotic work, since it is as a result of the movement of charged particles through membranes that a membrane charge is formed and the properties of excitability and conductivity are acquired. Mechanical work involves the movement of substances and structures inside the cell, as well as the cell as a whole. Regulatory work includes all processes aimed at coordinating processes in the cell.

Photosynthesis, its significance, cosmic role

Photosynthesis is the process of converting light energy into the energy of chemical bonds of organic compounds with the participation of chlorophyll.

As a result of photosynthesis, about 150 billion tons of organic matter and approximately 200 billion tons of oxygen are produced annually. This process ensures the carbon cycle in the biosphere, preventing carbon dioxide from accumulating and thereby preventing the greenhouse effect and overheating of the Earth. Organic substances formed as a result of photosynthesis are not completely consumed by other organisms; a significant part of them over the course of millions of years has formed deposits of minerals (hard and brown coal, oil). IN Lately Rapeseed oil (“biodiesel”) and alcohol obtained from plant residues also began to be used as fuel. Ozone is formed from oxygen under the influence of electrical discharges, which forms an ozone screen that protects all life on Earth from the destructive effects of ultraviolet rays.

Our compatriot, the outstanding plant physiologist K. A. Timiryazev (1843-1920), called the role of photosynthesis “cosmic”, since it connects the Earth with the Sun (space), providing an influx of energy to the planet.

Phases of photosynthesis. Light and dark reactions of photosynthesis, their relationship

In 1905, the English plant physiologist F. Blackman discovered that the rate of photosynthesis cannot increase indefinitely; some factor limits it. Based on this, he hypothesized that there are two phases of photosynthesis: light And dark. At low light intensity, the rate of light reactions increases in proportion to the increase in light intensity, and, in addition, these reactions do not depend on temperature, since they do not require enzymes to occur. Light reactions occur on thylakoid membranes.

The rate of dark reactions, on the contrary, increases with increasing temperature, however, upon reaching a temperature threshold of $30°C$, this increase stops, which indicates the enzymatic nature of these transformations occurring in the stroma. It should be noted that light also has a certain effect on dark reactions, despite the fact that they are called dark reactions.

The light phase of photosynthesis occurs on thylakoid membranes carrying several types of protein complexes, the main of which are photosystems I and II, as well as ATP synthase. Photosystems include pigment complexes, which, in addition to chlorophyll, also contain carotenoids. Carotenoids capture light in areas of the spectrum where chlorophyll does not, and also protect chlorophyll from destruction by high-intensity light.

In addition to pigment complexes, photosystems also include a number of electron acceptor proteins, which sequentially transfer electrons from chlorophyll molecules to each other. The sequence of these proteins is called electron transport chain of chloroplasts.

A special complex of proteins is also associated with photosystem II, which ensures the release of oxygen during photosynthesis. This oxygen-releasing complex contains manganese and chlorine ions.

IN light phase light quanta, or photons, falling on chlorophyll molecules located on thylakoid membranes, transfer them to an excited state, characterized by a more high energy electrons. In this case, excited electrons from the chlorophyll of photosystem I are transferred through a chain of intermediaries to the hydrogen carrier NADP, which attaches hydrogen protons, always present in an aqueous solution:

$NADP + 2e^(-) + 2H^(+) → NADPH + H^(+)$.

The reduced $NADPH + H^(+)$ will subsequently be used in the dark stage. Electrons from the chlorophyll of photosystem II are also transferred along the electron transport chain, but they fill the “electron holes” of the chlorophyll of photosystem I. The lack of electrons in the chlorophyll of photosystem II is filled by taking away water molecules, which occurs with the participation of the oxygen-releasing complex already mentioned above. As a result of the decomposition of water molecules, which is called photolysis, hydrogen protons are formed and molecular oxygen is released, which is a by-product of photosynthesis:

$H_2O → 2H^(+) + 2e^(-) + (1)/(2)O_2$.

Genetic information in a cell. Genes, genetic code and its properties. Matrix nature of biosynthesis reactions. Biosynthesis of protein and nucleic acids

Genetic information in a cell

Reproduction of one's own kind is one of the fundamental properties of living things. Thanks to this phenomenon, there is similarity not only between organisms, but also between individual cells, as well as their organelles (mitochondria and plastids). The material basis of this similarity is the transfer of genetic information encrypted in the DNA nucleotide sequence, which is carried out through the processes of DNA replication (self-duplication). All the characteristics and properties of cells and organisms are realized thanks to proteins, the structure of which is primarily determined by the sequence of DNA nucleotides. Therefore, the biosynthesis of nucleic acids and proteins plays paramount importance in metabolic processes. The structural unit of hereditary information is the gene.

Genes, genetic code and its properties

Hereditary information in a cell is not monolithic; it is divided into separate “words” - genes.

Gene is an elementary unit of genetic information.

Work on the “Human Genome” program, which was carried out simultaneously in several countries and was completed at the beginning of this century, gave us an understanding that a person has only about 25-30 thousand genes, but information from most of our DNA is never read, since it contains a huge number of meaningless sections, repeats and genes encoding traits that have lost meaning for humans (tail, body hair, etc.). In addition, a number of genes responsible for the development of hereditary diseases, as well as drug target genes, have been deciphered. However practical use The results obtained during the implementation of this program are postponed until the genomes of more people are deciphered and it becomes clear how they differ.

Genes that encode the primary structure of protein, ribosomal or transfer RNA are called structural, and genes that provide activation or suppression of reading information from structural genes - regulatory. However, even structural genes contain regulatory regions.

The hereditary information of organisms is encrypted in DNA in the form of certain combinations of nucleotides and their sequence - genetic code. Its properties are: tripletity, specificity, universality, redundancy and non-overlapping. In addition, there are no punctuation marks in the genetic code.

Each amino acid is encoded in DNA by three nucleotides - triplet, for example, methionine is encoded by the TAC triplet, that is, the code is triplet. On the other hand, each triplet encodes only one amino acid, which is its specificity or unambiguity. The genetic code is universal for all living organisms, that is, hereditary information about human proteins can be read by bacteria and vice versa. This indicates the unity of origin of the organic world. However, 64 combinations of three nucleotides correspond to only 20 amino acids, as a result of which one amino acid can be encoded by 2-6 triplets, that is, the genetic code is redundant or degenerate. Three triplets do not have corresponding amino acids, they are called stop codons, since they indicate the end of the synthesis of the polypeptide chain.

The sequence of bases in DNA triplets and the amino acids they encode

*Stop codon, indicating the end of the synthesis of the polypeptide chain.

Abbreviations for amino acid names:

Ala - alanine

Arg - arginine

Asn - asparagine

Asp - aspartic acid

Val - valine

His - histidine

Gly - glycine

Gln - glutamine

Glu - glutamic acid

Ile - isoleucine

Leu - leucine

Liz - lysine

Meth - methionine

Pro - proline

Ser - serine

Tyr - tyrosine

Tre - threonine

Three - tryptophan

Fen - phenylalanine

Cis - cysteine

If you start reading genetic information not from the first nucleotide in the triplet, but from the second, then not only will the reading frame shift, but the protein synthesized in this way will be completely different not only in the nucleotide sequence, but also in structure and properties. There are no punctuation marks between the triplets, so there are no obstacles to shifting the reading frame, which opens up space for the occurrence and maintenance of mutations.

Matrix nature of biosynthesis reactions

Bacterial cells are capable of doubling every 20-30 minutes, and eukaryotic cells - every day and even more often, which requires high speed and accuracy of DNA replication. In addition, each cell contains hundreds and thousands of copies of many proteins, especially enzymes, therefore, the “piecemeal” method of their production is unacceptable for their reproduction. A more progressive method is stamping, which allows you to obtain numerous exact copies of the product and also reduce its cost. For stamping, a matrix is required from which the impression is made.

In cells the principle matrix synthesis lies in the fact that new molecules of proteins and nucleic acids are synthesized in accordance with the program embedded in the structure of pre-existing molecules of the same nucleic acids (DNA or RNA).

Biosynthesis of protein and nucleic acids

DNA replication. DNA is a double-stranded biopolymer, the monomers of which are nucleotides. If DNA biosynthesis occurred on the principle of photocopying, then numerous distortions and errors in hereditary information would inevitably arise, which would ultimately lead to the death of new organisms. Therefore, the process of DNA doubling occurs differently, in a semi-conservative way: the DNA molecule unwinds, and a new chain is synthesized on each of the chains according to the principle of complementarity. The process of self-reproduction of a DNA molecule, ensuring accurate copying of hereditary information and its transmission from generation to generation, is called replication(from lat. replicationo- repetition). As a result of replication, two absolutely exact copies of the mother DNA molecule are formed, each of which carries one copy of the mother DNA molecule.

The replication process is actually extremely complex, since a number of proteins are involved in it. Some of them unwind the double helix of DNA, others break the hydrogen bonds between the nucleotides of complementary chains, others (for example, the enzyme DNA polymerase) select new nucleotides based on the principle of complementarity, etc. Two DNA molecules formed as a result of replication diverge into two during division newly formed daughter cells.

Errors in the replication process occur extremely rarely, but if they do occur, they are very quickly eliminated by both DNA polymerases and special repair enzymes, since any error in the nucleotide sequence can lead to an irreversible change in the structure and functions of the protein and, ultimately, adversely affect the viability of a new cell or even an individual.

Protein biosynthesis. As the outstanding philosopher of the 19th century F. Engels figuratively put it: “Life is a form of existence of protein bodies.” The structure and properties of protein molecules are determined by their primary structure, i.e., the sequence of amino acids encoded in DNA. Not only the existence of the polypeptide itself, but also the functioning of the cell as a whole depends on the accuracy of the reproduction of this information, so the process of protein synthesis is of great importance. It appears to be the most complex synthesis process in the cell, since it involves up to three hundred different enzymes and other macromolecules. In addition, it flows at high speed, which requires even greater precision.

There are two main stages in protein biosynthesis: transcription and translation.

Transcription(from lat. transcription- rewriting) is the biosynthesis of mRNA molecules on a DNA matrix.

Since the DNA molecule contains two antiparallel chains, reading information from both chains would lead to the formation of completely different mRNAs, therefore their biosynthesis is possible only on one of the chains, which is called coding, or codogenic, in contrast to the second, non-coding, or non-codogenic. The rewriting process is ensured by a special enzyme, RNA polymerase, which selects RNA nucleotides according to the principle of complementarity. This process can occur both in the nucleus and in organelles that have their own DNA - mitochondria and plastids.

The mRNA molecules synthesized during transcription undergo a complex process of preparation for translation (mitochondrial and plastid mRNAs can remain inside the organelles, where the second stage of protein biosynthesis occurs). During the process of mRNA maturation, the first three nucleotides (AUG) and a tail of adenyl nucleotides are attached to it, the length of which determines how many copies of the protein can be synthesized on a given molecule. Only then do mature mRNAs leave the nucleus through nuclear pores.

In parallel, the process of amino acid activation occurs in the cytoplasm, during which the amino acid joins the corresponding free tRNA. This process is catalyzed by a special enzyme and requires ATP.

Broadcast(from lat. broadcast- transfer) is the biosynthesis of a polypeptide chain on an mRNA matrix, during which genetic information is translated into the amino acid sequence of the polypeptide chain.

The second stage of protein synthesis most often occurs in the cytoplasm, for example on the rough ER. For its occurrence, the presence of ribosomes, activation of tRNA, during which they attach the corresponding amino acids, the presence of Mg2+ ions, as well as optimal environmental conditions (temperature, pH, pressure, etc.) are necessary.

To start broadcasting ( initiation) a small ribosomal subunit is attached to an mRNA molecule ready for synthesis, and then, according to the principle of complementarity to the first codon (AUG), a tRNA carrying the amino acid methionine is selected. Only after this does the large ribosomal subunit attach. Within the assembled ribosome there are two mRNA codons, the first of which is already occupied. A second tRNA, also carrying an amino acid, is added to the codon adjacent to it, after which a peptide bond is formed between the amino acid residues with the help of enzymes. The ribosome moves one codon of the mRNA; the first tRNA freed from an amino acid returns to the cytoplasm after the next amino acid, and a fragment of the future polypeptide chain hangs, as it were, on the remaining tRNA. The next tRNA is attached to the new codon that finds itself within the ribosome, the process is repeated and step by step the polypeptide chain lengthens, i.e. elongation.

End of protein synthesis ( termination) occurs as soon as a specific nucleotide sequence is encountered in the mRNA molecule that does not code for an amino acid (stop codon). After this, the ribosome, mRNA and polypeptide chain are separated, and the newly synthesized protein acquires the appropriate structure and is transported to the part of the cell where it will perform its functions.

Translation is a very energy-intensive process, since the energy of one ATP molecule is consumed to attach one amino acid to tRNA, and several more are used to move the ribosome along the mRNA molecule.

To speed up the synthesis of certain protein molecules, several ribosomes can be successively attached to an mRNA molecule, which form a single structure - polysome.

A cell is the genetic unit of a living thing. Chromosomes, their structure (shape and size) and functions. The number of chromosomes and their species constancy. Somatic and germ cells. Cell life cycle: interphase and mitosis. Mitosis is the division of somatic cells. Meiosis. Phases of mitosis and meiosis. Development of germ cells in plants and animals. Cell division is the basis for the growth, development and reproduction of organisms. The role of meiosis and mitosis

A cell is the genetic unit of a living thing.

Despite the fact that nucleic acids are the carrier of genetic information, the implementation of this information is impossible outside the cell, which is easily proven by the example of viruses. These organisms, often containing only DNA or RNA, cannot reproduce independently; to do this, they must use the hereditary apparatus of the cell. They cannot even penetrate a cell without the help of the cell itself, except through the use of membrane transport mechanisms or due to cell damage. Most viruses are unstable; they die after just a few hours of exposure to the open air. Consequently, a cell is a genetic unit of a living thing, which has a minimum set of components for preserving, changing and implementing hereditary information, as well as its transmission to descendants.

Most of the genetic information of a eukaryotic cell is located in the nucleus. The peculiarity of its organization is that, unlike the DNA of a prokaryotic cell, the DNA molecules of eukaryotes are not closed and form complex complexes with proteins - chromosomes.

Chromosomes, their structure (shape and size) and functions

Chromosome(from Greek chromium- color, coloring and soma- body) is the structure of the cell nucleus, which contains genes and carries certain hereditary information about the characteristics and properties of the organism.

Sometimes the circular DNA molecules of prokaryotes are also called chromosomes. Chromosomes are capable of self-duplication; they have structural and functional individuality and retain it over generations. Each cell carries all the hereditary information of the body, but only a small part works in it.

The basis of a chromosome is a double-stranded DNA molecule packed with proteins. In eukaryotes, histone and non-histone proteins interact with DNA, whereas in prokaryotes, histone proteins are absent.

Chromosomes are best seen under a light microscope during cell division, when, as a result of compaction, they take on the appearance of rod-shaped bodies separated by a primary constriction - centromere — on shoulders. On a chromosome there may also be secondary constriction, which in some cases separates the so-called satellite. The ends of chromosomes are called telomeres. Telomeres prevent the ends of chromosomes from sticking together and ensure their attachment to the nuclear membrane in a non-dividing cell. At the beginning of division, the chromosomes are doubled and consist of two daughter chromosomes - chromatid, fastened at the centromere.

According to their shape, chromosomes are divided into equal-armed, unequal-armed and rod-shaped chromosomes. The sizes of chromosomes vary significantly, but the average chromosome has dimensions of 5 $×$ 1.4 microns.

In some cases, chromosomes, as a result of numerous DNA duplications, contain hundreds and thousands of chromatids: such giant chromosomes are called polytene. They are found in the salivary glands of Drosophila larvae, as well as in the digestive glands of roundworms.

The number of chromosomes and their species constancy. Somatic and germ cells

According to cellular theory, a cell is a unit of structure, vital activity and development of an organism. Thus, such important functions of living things as growth, reproduction and development of the organism are provided at the cellular level. Cells of multicellular organisms can be divided into somatic and reproductive cells.

Somatic cells- these are all the cells of the body formed as a result of mitotic division.

The study of chromosomes has made it possible to establish that the somatic cells of the body of each biological species are characterized by a constant number of chromosomes. For example, a person has 46 of them. The set of chromosomes of somatic cells is called diploid(2n), or double.

Sex cells, or gametes, are specialized cells used for sexual reproduction.

Gametes always contain half as many chromosomes as somatic cells (in humans - 23), therefore the set of chromosomes of germ cells is called haploid(n), or single. Its formation is associated with meiotic cell division.

The amount of DNA in somatic cells is designated as 2c, and in sex cells - 1c. The genetic formula of somatic cells is written as 2n2c, and sexual cells - 1n1c.

In the nuclei of some somatic cells, the number of chromosomes may differ from their number in somatic cells. If this difference is greater than one, two, three, etc. haploid sets, then such cells are called polyploid(tri-, tetra-, pentaploid, respectively). In such cells, metabolic processes usually proceed very intensively.

The number of chromosomes in itself is not a species-specific feature, since different organisms can have an equal number of chromosomes, but related ones can have a different number. For example, the malarial plasmodium and the horse roundworm each have two chromosomes, while humans and chimpanzees have 46 and 48, respectively.

Human chromosomes are divided into two groups: autosomes and sex chromosomes (heterochromosomes). Autosome in human somatic cells there are 22 pairs, they are the same for men and women, and sex chromosomes only one pair, but it is this that determines the sex of the individual. There are two types of sex chromosomes - X and Y. Women's body cells carry two X chromosomes, and men's - X and Y.

Karyotype is a set of signs chromosome set organism (number of chromosomes, their shape and size).

The conditional record of a karyotype includes the total number of chromosomes, sex chromosomes and possible deviations in the set of chromosomes. For example, karyotype normal man is written as 46, XY, and the karyotype of a normal woman is 46, XX.

Cell life cycle: interphase and mitosis

Cells do not arise anew every time, they are formed only as a result of the division of mother cells. After division, the daughter cells require some time to form organelles and acquire the appropriate structure that would ensure the performance of a specific function. This period of time is called maturation.

The period of time from the appearance of a cell as a result of division until its division or death is called life cycle of a cell.

In eukaryotic cells, the life cycle is divided into two main stages: interphase and mitosis.

Interphase- this is a period of time in the life cycle during which the cell does not divide and functions normally. Interphase is divided into three periods: G 1 -, S- and G 2 -periods.

G 1 -period(presynthetic, postmitotic) is a period of cell growth and development during which active synthesis of RNA, proteins and other substances necessary for the complete life support of the newly formed cell occurs. Towards the end of this period, the cell may begin to prepare to duplicate its DNA.

IN S-period(synthetic) the process of DNA replication itself occurs. The only part of the chromosome that does not undergo replication is the centromere, therefore the resulting DNA molecules do not diverge completely, but remain held together in it, and at the beginning of division the chromosome has X-shape. The genetic formula of a cell after DNA doubling is 2n4c. Also in the S-period, the centrioles of the cell center are doubled.

G 2 -period(postsynthetic, premitotic) is characterized by intensive synthesis of RNA, proteins and ATP necessary for the process of cell division, as well as the separation of centrioles, mitochondria and plastids. Until the end of interphase, chromatin and the nucleolus remain clearly distinguishable, the integrity of the nuclear envelope is not disrupted, and the organelles do not change.

Some of the body's cells are able to perform their functions throughout the life of the body (neurons of our brain, muscle cells of the heart), while others exist for a short time, after which they die (intestinal epithelial cells, epidermal cells of the skin). Consequently, the body must constantly undergo processes of cell division and the formation of new ones that would replace dead ones. Cells capable of dividing are called stem. In the human body they are found in the red bone marrow, in the deep layers of the epidermis of the skin and other places. Using these cells it is possible to grow new organ, achieve rejuvenation, and also clone the body. The prospects for using stem cells are absolutely clear, but the moral and ethical aspects of this problem are still being discussed, since in most cases embryonic stem cells obtained from human embryos killed during abortion are used.

The duration of interphase in plant and animal cells averages 10-20 hours, while mitosis takes about 1-2 hours.

During successive divisions in multicellular organisms, daughter cells become increasingly diverse as they read information from all more genes.

Some cells stop dividing over time and die, which may be due to the completion of certain functions, as in the case of epidermal skin cells and blood cells, or due to damage to these cells by environmental factors, in particular pathogens. Genetically programmed cell death is called apoptosis, while accidental death - necrosis.

Mitosis is the division of somatic cells. Phases of mitosis

Mitosis- a method of indirect division of somatic cells.

During mitosis, the cell goes through a series of successive phases, as a result of which each daughter cell receives the same set of chromosomes as in the mother cell.

Mitosis is divided into four main phases: prophase, metaphase, anaphase and telophase. Prophase- the longest stage of mitosis, during which chromatin condenses, resulting in X-shaped chromosomes consisting of two chromatids (daughter chromosomes) becoming visible. In this case, the nucleolus disappears, the centrioles diverge to the poles of the cell, and an achromatin spindle (division spindle) from microtubules begins to form. At the end of prophase, the nuclear membrane disintegrates into separate vesicles.

IN metaphase The chromosomes are lined up along the equator of the cell with their centromeres, to which the microtubules of the fully formed spindle are attached. At this stage of division, the chromosomes are most compacted and have characteristic shape, which allows you to study the karyotype.

IN anaphase Rapid DNA replication occurs at centromeres, as a result of which chromosomes are split and chromatids diverge to the poles of the cell, stretched by microtubules. The distribution of chromatids must be absolutely equal, since it is this process that ensures the maintenance of a constant number of chromosomes in the cells of the body.

On the stage telophases daughter chromosomes gather at the poles, despiral, nuclear membranes form around them from vesicles, and nucleoli appear in the newly formed nuclei.

After nuclear division, cytoplasmic division occurs - cytokinesis, during which a more or less uniform distribution of all organelles of the mother cell occurs.

Thus, as a result of mitosis, two daughter cells are formed from one mother cell, each of which is a genetic copy of the mother cell (2n2c).

In sick, damaged, aging cells and specialized tissues of the body, a slightly different division process can occur - amitosis. Amitosis called direct division of eukaryotic cells, in which the formation of genetically equivalent cells does not occur, since the cellular components are distributed unevenly. It is found in plants in the endosperm, and in animals - in the liver, cartilage and cornea of the eye.

Meiosis. Phases of meiosis

Meiosis is a method of indirect division of primary germ cells (2n2c), which results in the formation of haploid cells (1n1c), most often germ cells.

Unlike mitosis, meiosis consists of two successive cell divisions, each of which is preceded by interphase. The first division of meiosis (meiosis I) is called reductionist, since in this case the number of chromosomes is halved, and the second division (meiosis II) - equational, since in its process the number of chromosomes is preserved.

Interphase I proceeds like interphase of mitosis. Meiosis I is divided into four phases: prophase I, metaphase I, anaphase I and telophase I. B prophase I Two important processes occur: conjugation and crossing over. Conjugation- This is the process of fusion of homologous (paired) chromosomes along the entire length. The pairs of chromosomes formed during conjugation are preserved until the end of metaphase I.

Crossing over- mutual exchange of homologous regions of homologous chromosomes. As a result of crossing over, the chromosomes received by the body from both parents acquire new combinations of genes, which causes the appearance of genetically diverse offspring. At the end of prophase I, as in the prophase of mitosis, the nucleolus disappears, the centrioles diverge to the poles of the cell, and the nuclear membrane disintegrates.

IN metaphase I pairs of chromosomes are aligned along the equator of the cell, and spindle microtubules are attached to their centromeres.

IN anaphase I Whole homologous chromosomes, consisting of two chromatids, diverge to the poles.

IN telophase I Nuclear membranes are formed around clusters of chromosomes at the poles of the cell, and nucleoli are formed.

Cytokinesis I ensures separation of the cytoplasms of daughter cells.

The daughter cells (1n2c) formed as a result of meiosis I are genetically heterogeneous, since their chromosomes, randomly dispersed to the cell poles, contain different genes.

Comparative characteristics of mitosis and meiosis

Sign	Mitosis	Meiosis
Which cells begin to divide?	Somatic (2n)	Primary germ cells (2n)
Number of divisions	1	2
How many and what kind of cells are formed during division?	2 somatic (2n)	4 sexual (n)
Interphase		Preparing the cell for division, DNA doubling	Very short, DNA doubling does not occur
Phases		Meiosis I	Meiosis II
Prophase		Chromosome condensation, disappearance of the nucleolus, disintegration of the nuclear membrane, conjugation and crossing over may occur	Chromosome condensation, disappearance of the nucleolus, disintegration of the nuclear membrane
Metaphase		Pairs of chromosomes are located along the equator, a spindle is formed	Chromosomes line up along the equator, a spindle is formed
Anaphase		Homologous chromosomes from two chromatids move towards the poles	Chromatids move towards the poles
Telophase		Chromosomes despiral, new nuclear membranes and nucleoli are formed	Chromosomes despiral, new nuclear membranes and nucleoli are formed

Interphase II very short, since DNA doubling does not occur in it, that is, there is no S-period.

Meiosis II also divided into four phases: prophase II, metaphase II, anaphase II and telophase II. IN prophase II the same processes occur as in prophase I, with the exception of conjugation and crossing over.

IN metaphase II chromosomes are located along the equator of the cell.

IN anaphase II chromosomes are split at centromeres and chromatids are stretched towards the poles.

IN telophase II Nuclear membranes and nucleoli are formed around clusters of daughter chromosomes.

After cytokinesis II The genetic formula of all four daughter cells is 1n1c, but they all have a different set of genes, which is the result of crossing over and the random combination of chromosomes of the maternal and paternal organisms in the daughter cells.

Development of germ cells in plants and animals

Gametogenesis(from Greek gamete- wife, gametes- husband and genesis- origin, emergence) is the process of formation of mature germ cells.

Since sexual reproduction most often requires two individuals - a female and a male, producing different sex cells - eggs and sperm, then the processes of formation of these gametes must be different.

The nature of the process depends to a significant extent on whether it occurs in a plant or animal cell, since in plants only mitosis occurs during the formation of gametes, and in animals both mitosis and meiosis occur.

Development of germ cells in plants. In angiosperms, the formation of male and female reproductive cells occurs in different parts of the flower - the stamens and pistils, respectively.

Before the formation of male reproductive cells - microgametogenesis(from Greek micros- small) - happens microsporogenesis, that is, the formation of microspores in the anthers of stamens. This process is associated with the meiotic division of the mother cell, which results in four haploid microspores. Microgametogenesis is associated with mitotic division of the microspore, giving a male gametophyte from two cells - a large vegetative(siphonogenic) and shallow generative. After division, the male gametophyte becomes covered with dense membranes and forms a pollen grain. In some cases, even during the process of pollen maturation, and sometimes only after transfer to the stigma of the pistil, the generative cell divides mitotically to form two immobile male germ cells - sperm. After pollination, a pollen tube is formed from the vegetative cell, through which sperm penetrate into the ovary of the pistil for fertilization.

The development of female germ cells in plants is called megagametogenesis(from Greek megas- big). It occurs in the ovary of the pistil, which is preceded by megasporogenesis, as a result of which four megaspores are formed from the mother cell of the megaspore lying in the nucellus through meiotic division. One of the megaspores divides mitotically three times, giving the female gametophyte - an embryo sac with eight nuclei. With the subsequent separation of the cytoplasms of the daughter cells, one of the resulting cells becomes an egg, on the sides of which lie the so-called synergids, at the opposite end of the embryo sac three antipodes are formed, and in the center, as a result of the fusion of two haploid nuclei, a diploid central cell is formed.

Development of germ cells in animals. In animals, there are two processes of formation of germ cells - spermatogenesis and oogenesis.

Spermatogenesis(from Greek sperm, spermatos- seed and genesis- origin, occurrence) is the process of formation of mature male germ cells - sperm. In humans, it occurs in the testes, or testicles, and is divided into four periods: reproduction, growth, maturation and formation.

IN breeding season primordial germ cells divide mitotically, resulting in the formation of diploid spermatogonia. IN growth period spermatogonia accumulate nutrients in the cytoplasm, increase in size and turn into primary spermatocytes, or 1st order spermatocytes. Only after this do they enter meiosis ( maturation period), as a result of which first two are formed secondary spermatocyte, or 2nd order spermatocyte, and then four haploid cells with still enough big amount cytoplasm - spermatids. IN formation period they lose almost all their cytoplasm and form a flagellum, turning into sperm.

Sperm, or livelies, - very small mobile male reproductive cells with a head, neck and tail.

IN head, in addition to the core, is acrosome- a modified Golgi complex that ensures the dissolution of the egg membranes during fertilization. IN cervix are the centrioles of the cell center, and the base ponytail form microtubules that directly support sperm movement. It also contains mitochondria, which provide the sperm with ATP energy for movement.

Oogenesis(from Greek UN- egg and genesis- origin, occurrence) is the process of formation of mature female germ cells - eggs. In humans, it occurs in the ovaries and consists of three periods: reproduction, growth and maturation. Periods of reproduction and growth, similar to those in spermatogenesis, occur during intrauterine development. In this case, diploid cells are formed from primary germ cells as a result of mitosis. oogonia, which then turn into diploid primary oocytes, or 1st order oocytes. Meiosis and subsequent cytokinesis occurring in maturation period, are characterized by uneven division of the cytoplasm of the mother cell, so that as a result, at first one is obtained secondary oocyte, or 2nd order oocyte, And first polar body, and then from the secondary oocyte - the egg, which retains the entire supply of nutrients, and the second polar body, while the first polar body is divided into two. Polar bodies take up excess genetic material.

In humans, eggs are produced with an interval of 28-29 days. The cycle associated with the maturation and release of eggs is called menstrual.

Egg- a large female reproductive cell that carries not only a haploid set of chromosomes, but also a significant supply of nutrients for the subsequent development of the embryo.

The egg in mammals is covered with four membranes, which reduce the likelihood of damage by various factors. The diameter of the egg in humans reaches 150-200 microns, while in an ostrich it can be several centimeters.

Cell division is the basis for the growth, development and reproduction of organisms. The role of mitosis and meiosis

If in unicellular organisms cell division leads to an increase in the number of individuals, i.e., reproduction, then in multicellular organisms this process can have different meaning. Thus, the division of embryonic cells, starting from the zygote, is the biological basis of the interconnected processes of growth and development. Similar changes are observed in humans during adolescence, when the number of cells not only increases, but also a qualitative change in the body occurs. The reproduction of multicellular organisms is also based on cell division, for example, in asexual reproduction, thanks to this process, a whole part of the organism is restored, and in sexual reproduction, in the process of gametogenesis, sex cells are formed, which subsequently give rise to a new organism. It should be noted that the main methods of division of a eukaryotic cell - mitosis and meiosis - have different meanings in the life cycles of organisms.

As a result of mitosis, there is an even distribution of hereditary material between daughter cells - exact copies of the mother. Without mitosis, the existence and growth of multicellular organisms developing from a single cell, the zygote, would be impossible, since all cells of such organisms must contain the same genetic information.

During the process of division, daughter cells become more and more diverse in structure and functions, which is associated with the activation of more and more new groups of genes in them due to intercellular interaction. Thus, mitosis is necessary for the development of the organism.

This method of cell division is necessary for the processes asexual reproduction and regeneration (restoration) of damaged tissues, as well as organs.

Meiosis, in turn, ensures the constancy of the karyotype during sexual reproduction, since it halves the set of chromosomes before sexual reproduction, which is then restored as a result of fertilization. In addition, meiosis leads to the emergence of new combinations of parental genes due to crossing over and random combination of chromosomes in daughter cells. Thanks to this, the offspring turns out to be genetically diverse, which provides material for natural selection and is the material basis for evolution. A change in the number, shape and size of chromosomes, on the one hand, can lead to the appearance of various deviations in the development of the organism and even its death, and on the other hand, it can lead to the appearance of individuals more adapted to the environment.

Thus, the cell is the unit of growth, development and reproduction of organisms.

Question 1.
The cell contains about 80 chemical elements of D. I. Mendeleev’s periodic table. All these elements are also found in inanimate nature, which serves as one of the proofs of the commonality of living and inanimate nature. However, the ratio of chemical elements in living organisms is different than in inanimate objects. In a living organism, most elements are found in the form of chemical compounds - substances dissolved in water. Only living organisms contain organic substances: proteins, fats, carbohydrates and nucleic acids

Question 2.
Chemical composition similar to plant and animal cells. All living organisms consist of the same elements, inorganic and organic compounds. But the content of different elements in different cells differs. Each type of cell contains different amounts of certain organic molecules. Complex carbohydrates (fiber, starch) predominate in plant cells, while animal cells contain more proteins and fats. Each of the groups of organic substances (proteins, carbohydrates, fats, nucleic acids) in any type of cell performs its inherent functions (nucleic acid - storage and transmission of hereditary information, carbohydrates - energy, etc.).

Question 3.
Many elements of Mendeleev's periodic table were found in the cell. The functions of 27 of them have been defined. The most common are carbon, hydrogen, nitrogen, oxygen, phosphorus and sulfur. They make up 99% of the total cell mass.
The chemical elements that make up cells are divided into three groups: macronutrients, microelements, ultramicroelements.
1. Macronutrients: C, H, N, Ca, K, Mg, Na, Fe, S, P, C1. These elements account for more than 99% of the total cell mass. The concentration of some of them is high. Oxygen accounts for 65-75%; carbon - 15-18%; nitrogen - 1.5-3%.
2. Microelements: Cu, B, Co, Mo, Mn, Ni, Br, I and others. Their total share in the cell is more than 0.1%; the concentration of each does not exceed 0.001%. These are metal ions that are part of the biological active substances(hormones, enzymes, etc.). For example, cobalt is part of vitamin BO, C, H, N, Ca, K, Mg, Na, Fe 12, which is involved in hematopoiesis, and fluorine is included in tooth enamel cells.
3. Ultramicroelements: uranium, gold, beryllium, mercury, cesium, selenium and others. Their concentration does not exceed 0.000001%. The physiological role of many of them has not been established.

Question 4.
Organic compounds make up on average 10% of the cell mass of a living organism. These include biological polymers - proteins, nucleic acids and carbohydrates, as well as fats and a number of small molecules -

Question 5.
Squirrels- high molecular weight polymeric organic substances that determine the structure and vital activity of the cell and the organism as a whole. Proteins make up 10-18% of the total cell mass.
Proteins perform the following functions:
enzymatic (for example, amylase, breaks down carbohydrates);
structural (for example, they are part of cell membranes);
receptor (for example, rhodopsin, promotes better vision);
transport (for example, hemoglobin, carries oxygen or carbon dioxide);
protective (for example, immunoglobulins, involved in the formation of immunity);
motor (for example, actin, myosin, are involved in the contraction of muscle fibers);
hormonal (for example, insulin, converts glucose into glycogen);
energy (when 1 g of protein is broken down, 4.2 kcal of energy is released).

Question 6.
Carbohydrates play the role of the main source of energy in the cell. During the oxidation of 1 g of carbohydrates, 17.6 kJ of energy is released. Starch in plants and glycogen in animals, deposited in cells, serves as an energy reserve. Living organisms can store carbohydrates in the form of starch (in plants) and glycogen (in animals and fungi). In potato tubers, starch can make up up to 80% of the mass, and in animals there is especially a lot of carbohydrates in liver cells and muscles - up to 5%.
Carbohydrates also perform other functions, such as support and protection. For example, cellulose forms the walls of plant cells: a complex polysaccharide chitin- the main structural component of the exoskeleton of arthropods. Chitin also performs a construction function in fungi. They are part of DNA, RNA and ATP in the form of deoxyribose and ribose.

Question 7.
Fats perform a number of functions in the body:
structural (take part in the construction of the membrane);
energy (the breakdown of 1 g of fat in the body releases 9.2 kcal of energy - 2.5 times more than the breakdown of the same amount of carbohydrates);
protective (against heat loss, mechanical damage);
fat is a source of endogenous water (with the oxidation of 10 g of fat, 11 g of water is released). This is very important for animals that hibernate in winter - gophers, marmots: thanks to their subcutaneous fat reserves, they can not drink at this time for up to two months. When crossing the desert, camels go without drinking for up to two weeks - they extract the water necessary for the body from their humps, which are receptacles for fat.
regulation of metabolism (for example, steroid hormones - corticosterone, etc.).

Question 8.
The most common inorganic compound in living organisms is water. Its content in different types of cells varies widely: in the cells of tooth enamel there is about 10% water, and in the cells of a reproducing embryo - more than 90%. The body of a jellyfish contains up to 98% water. But on average, in a multicellular organism, water makes up about 80% of body weight. Its main functions are as follows:
1. Universal solvent.
2. The environment in which biochemical reactions occur.
3. Determines the physiological properties of the cell (its elasticity, volume).
4. Participates in chemical reactions.
5. Supports thermal equilibrium cells and the body as a whole due to high heat capacity and thermal conductivity.
6. The main means for transporting substances.

Question 9.
Carbohydrates include the following natural organic compounds: glucose, fructose, sucrose, maltose, lactose, ribose, deoxyribose, chitin, starch, glycogen and cellulose.

Question 10.
The importance of nucleic acids is very great. The peculiarities of their chemical structure provide the possibility of storing, transferring into the cytoplasm and inheriting to daughter cells information about the structure of protein molecules that are synthesized in each cell. They are part of chromosomes - special structures located in the cell nucleus. Nucleic acids are also found in the cytoplasm and its organelles.

Question 11.
In the earth's crust, the most abundant are silicon, aluminum, oxygen and sodium (about 90%). In living organisms, about 98% of the mass is made up of four elements: hydrogen, oxygen, carbon and nitrogen. This difference is due to the peculiarities of the chemical properties of the listed elements, as a result of which they turned out to be most suitable for the formation of molecules that perform biological functions. Hydrogen, oxygen, carbon and nitrogen are capable of forming strong chemical bonds, resulting in a wide variety of chemical compounds. Living organisms include organic substances (proteins, fats, carbohydrates, nucleic acids) and inorganic substances (water, mineral salts).

Cell as a biological system

Modern cell theory, its main provisions, role in the formation of the modern natural science picture of the world. Development of knowledge about the cell. The cellular structure of organisms is the basis of the unity of the organic world, proof of the kinship of living nature

Modern cell theory, its main provisions, role in the formation of the modern natural science picture of the world

Development of knowledge about the cell

The cellular structure of organisms, the similarity of the structure of the cells of all organisms is the basis of the unity of the organic world, evidence of the kinship of living nature

Diversity of cells. Prokaryotic and eukaryotic cells. Comparative characteristics of cells of plants, animals, bacteria, fungi Diversity of cells

Prokaryotic and eukaryotic cells

Comparative characteristics of the structure of cells of plants, animals, bacteria and fungi

Chemical composition of the cell. Macro- and microelements. The relationship between the structure and functions of inorganic and organic substances (proteins, nucleic acids, carbohydrates, lipids, ATP) that make up the cell. The role of chemicals in the cell and human body

Chemical composition of the cell

Macro- and microelements

The relationship between the structure and functions of inorganic and organic substances (proteins, nucleic acids, carbohydrates, lipids, ATP) that make up the cell. The role of chemicals in the cell and human body

Inorganic substances

Organic matter

General characteristics of the organic substances of the cell

Cell structure. The relationship between the structure and functions of the parts and organelles of a cell is the basis of its integrity

Cell structure

Cytoplasm

Organoids

Inclusions

The relationship between the structure and functions of the parts and organelles of a cell is the basis of its integrity

Metabolism and energy conversion - properties of living organisms

Energy and plastic metabolism, their relationship

Stages of energy metabolism

Breath

Fermentation

Photosynthesis, its significance, cosmic role

Phases of photosynthesis. Light and dark reactions of photosynthesis, their relationship

Genetic information in a cell. Genes, genetic code and its properties. Matrix nature of biosynthesis reactions. Biosynthesis of protein and nucleic acids

Genetic information in a cell

Genes, genetic code and its properties

Matrix nature of biosynthesis reactions

Biosynthesis of protein and nucleic acids

A cell is the genetic unit of a living thing.

Chromosomes, their structure (shape and size) and functions

The number of chromosomes and their species constancy. Somatic and germ cells

Cell life cycle: interphase and mitosis

Mitosis is the division of somatic cells. Phases of mitosis

Meiosis. Phases of meiosis

Development of germ cells in plants and animals

Cell division is the basis for the growth, development and reproduction of organisms. The role of mitosis and meiosis

New on the site

Most popular

POPULAR SECTIONS