Functions and characteristics of protein table. Types of proteins and their functions in the human body

Structure of protein molecules. Relationship between the properties, functions and activity of proteins with their structural organization (specificity, species, recognition effect, dynamism, effect of cooperative interaction).

Squirrels are high-molecular nitrogen-containing substances consisting of amino acid residues linked by peptide bonds. Proteins are otherwise called proteins;

Simple proteins are built from amino acids and, upon hydrolysis, break down only into amino acids. Complex proteins are two-component proteins that consist of some simple protein and a non-protein component called a prosthetic group. During the hydrolysis of complex proteins, in addition to free amino acids, the non-protein part or its breakdown products are released. Simple proteins, in turn, are divided based on some conditionally selected criteria into a number of subgroups: protamines, histones, albumins, globulins, prolamins, glutelins, etc.

The classification of complex proteins is based on the chemical nature of their non-protein component. In accordance with this, they distinguish: phosphoproteins (contain phosphoric acid), chromoproteins (they contain pigments), nucleoproteins (contain nucleic acids), glycoproteins (contain carbohydrates), lipoproteins (contain lipids) and metalloproteins (contain metals).

3. Protein structure.

The sequence of amino acid residues in the polypeptide chain of a protein molecule is called primary protein structure. The primary structure of a protein, in addition to a large number of peptide bonds, usually also contains a small number of disulfide (-S-S-) bonds. Spatial configuration of the polypeptide chain, more precisely the type polypeptide helix, definessecondary protein structure, it is presented in mainly α-helix, which is fixed by hydrogen bonds. tertiary structure- a polypeptide chain, folded entirely or partially into a spiral, located or packed in space (in a globule). The known stability of the tertiary structure of the protein is ensured by hydrogen bonds, intermolecular van der Waals forces, electrostatic interaction of charged groups, etc.

Quaternary protein structure - a structure consisting of a certain number of polypeptide chains occupying a strictly fixed position relative to each other.

A classic example of a protein having a quaternary structure is hemoglobin.

Physical properties of proteins: high viscosity of solutions,

insignificant diffusion, ability to swell within large limits, optical activity, mobility in an electric field, low osmotic pressure and high oncotic pressure, ability to absorb UV rays at 280 nm, like amino acids, are amphoteric due to the presence of free NH2 and COOH groups and are characterized accordingly by all the properties of acids and bases. They have pronounced hydrophilic properties. Their solutions have very low osmotic pressure, high viscosity and low diffusion ability. Proteins are capable of swelling within very large limits. The colloidal state of proteins is associated with the phenomenon of light scattering, which underlies the quantitative determination of proteins by nephelometry.

Proteins are capable of adsorbing low molecular weight organic compounds and inorganic ions on their surface. This property determines the transport functions of individual proteins.

Chemical properties of proteins are diverse, since the side radicals of amino acid residues contain different functional groups (-NH2, -COOH, -OH, -SH, etc.). A characteristic reaction for proteins is the hydrolysis of peptide bonds. Due to the presence of both amino and carboxyl groups, proteins have amphoteric properties.

Protein denaturation- destruction of bonds that stabilize the quaternary, tertiary and secondary structures, leading to disorientation of the configuration of the protein molecule and accompanied by the loss of native properties.

There are physical (temperature, pressure, mechanical stress, ultrasonic and ionizing radiation) and chemical (heavy metals, acids, alkalis, organic solvents, alkaloids) factors that cause denaturation.

The reverse process is renaturation, that is, restoration of the physicochemical and biological properties of the protein. Renaturation is not possible if the primary structure is affected.

Most proteins are denatured when they are heated with a solution above 50-60 o C. External manifestations of denaturation are reduced to loss of solubility, especially at the isoelectric point, an increase in the viscosity of protein solutions, an increase in the amount of free functional SH-rpypp and a change in the nature of x-ray scattering, globules of native protein unfold molecules and random and disordered structures are formed.

Contractile function. actin and myosin are specific proteins of muscle tissue. Structural function. fibrillar proteins, in particular collagen in connective tissue, keratin in hair, nails, skin, elastin in the vascular wall, etc.

Hormonal function. A number of hormones are represented by proteins or polypeptides, for example, hormones of the pituitary gland, pancreas, etc. Some hormones are derivatives of amino acids.

Nutritional (reserve) function. reserve proteins, which are sources of nutrition for the fetus. The main protein of milk (casein) also performs mainly a nutritional function.

Biological functions of proteins. Diversity of proteins in structural organization and biological function. Polymorphism. Differences in the protein composition of organs and tissues. Changes in composition during ontogenesis and in diseases.

-By degree of difficulty The structures of proteins are divided into simple and complex. Simple or one-component proteins consist only of the protein part and upon hydrolysis yield amino acids. TO complex or two-component include proteins V which includes protein and an additional group of non-protein nature, called prosthetic. ( can be lipids, carbohydrates, nucleic acids); Accordingly, complex proteins are called lipoproteins, glycoproteins, nucleoproteins.

- According to the shape of the protein molecule proteins are divided into two groups: fibrillar (fibrous) and globular (corpuscular). Fibrillar proteins characterized by a high ratio of their length to diameter (several tens of units). Their molecules are filamentous and are usually collected in bundles that form fibers. (are the main components of the outer layer of skin, forming the protective covers of the human body). They are also involved in the formation of connective tissue, including cartilage and tendons.

The overwhelming majority of natural proteins are globular. For globular proteins characterized by a small ratio of length to diameter of the molecule (several units). Having a more complex conformation, globular proteins perform more diverse functions.

-In relation to conventionally selected solvents allocate albuminsAndglobulins. Albumin dissolves very well V water and concentrated saline solutions. Globulins do not dissolve in water and V solutions of salts of moderate concentration..

--Functional classification of proteins the most satisfactory, since it is based not on a random sign, but on a performed function. In addition, we can highlight the similarity of structures, properties and functional activities of specific proteins included in any class.

Catalytically active proteins called enzymes. They catalyze almost all chemical transformations in the cell. This group of proteins will be discussed in detail in Chapter 4.

Hormones regulate metabolism within cells and integrate metabolism in various cells of the body as a whole.

Receptors selectively bind various regulators (hormones, mediators) on the surface of cell membranes.

Transport proteins carry out binding and transport of substances between tissues and through cell membranes.

Structural proteins . First of all, this group includes proteins involved in the construction of various biological membranes.

Squirrels - inhibitors enzymes constitute a large group of endogenous inhibitors. They regulate enzyme activity.

Contractives squirrels provide a mechanical reduction process using chemical energy.

Toxic proteins - some proteins and peptides secreted by organisms (snakes, bees, microorganisms) that are poisonous to other living organisms.

Protective proteins. antibodies - protein substances produced by the animal body in response to the introduction of an antigen. Antibodies, interacting with antigens, deactivate them and thereby protect the body from the effects of foreign compounds, viruses, bacteria, etc.

Protein composition depends on physiological. Activity, food composition and diet, biorhythms. During development, the composition changes significantly (from the zygote to the formation of differentiated organs with specialized functions). For example, red blood cells contain hemoglobin, which ensures the transport of oxygen in the blood, mouse cells contain the contractile proteins actin and myosin, the retina contains the protein rhodopsin, etc. In diseases, the protein composition changes—proteinopathies. Hereditary proteinopathies develop as a result of damage to the genetic apparatus. A protein is not synthesized at all or is synthesized, but its primary structure is changed (sickle cell anemia). Any disease is accompanied by a change in protein composition, i.e. acquired proteinopathy develops. In this case, the primary structure of proteins is not disrupted, but a quantitative change in proteins occurs, especially in those organs and tissues in which the pathological process develops. For example, with pancreatitis, the production of enzymes necessary for the digestion of nutrients in the gastrointestinal tract decreases.

Factors of damage to the structure and function of proteins, the role of damage in the pathogenesis of diseases. Proteinopathies

The protein composition of the body of a healthy adult is relatively constant, although changes in the amount of individual proteins in organs and tissues are possible. Various diseases cause changes in the protein composition of tissues. These changes are called proteinopathies. There are hereditary and acquired proteinopathies. Hereditary proteinopathies develop as a result of damage to the genetic apparatus of a given individual. A protein is not synthesized at all or is synthesized but is primary structure changed. Any disease is accompanied by a change in the protein composition of the body, i.e. acquired proteinopathy develops. In this case, the primary structure of proteins is not disturbed, but usually a quantitative change in proteins occurs, especially in those organs and tissues in which the pathological process develops. For example, with pancreatitis, the production of enzymes necessary for the digestion of nutrients in the gastrointestinal tract decreases.

In some cases, acquired proteinopathies develop as a result of changes in the conditions in which proteins function. Thus, when the pH of the environment changes to the alkaline side (alkaloses of various natures), the conformation of hemoglobin changes, its affinity for O2 increases and the delivery of O2 to tissues decreases (tissue hypoxia).

Sometimes, as a result of the disease, the level of metabolites in blood cells and serum increases, which leads to the modification of certain proteins and disruption of their function

In addition, proteins that are normally detected there only in trace amounts can be released from the cells of the damaged organ into the blood. For various diseases, biochemical studies of the protein composition of the blood are often used to clarify the clinical diagnosis.

4. Primary structure of proteins. Dependence of the properties and functions of proteins on their primary structure. Changes in the primary structure, proteinopathy.

Lesson on learning new material in 10th grade. Students have already studied this material in 9th grade, so they already know some concepts. Accordingly, a dialogue is conducted with the children about the structure and functions of proteins. With the help of the teacher, students learn about the classification of enzymes.

In order to intensify the activity of students in the lesson, interesting facts about proteins are given that help the children and aim them at further learning new material. It is also proposed to conduct laboratory work for these purposes. In this lesson, the bulk of the material being studied is written down in the form of tables and diagrams, which the teacher builds during the lesson together with the students. The quality of the material being studied is checked in the form of a frontal survey. The lesson is designed for both auditory and visual children.

Purpose of the lesson: to provide an understanding of the structure and function of proteins.

Objectives: to continue to expand and deepen knowledge of the most important organic substances of the cell based on the study of the structure and function of proteins, to develop knowledge of the functions of proteins and their most important role in organic world, continue to develop the ability to identify connections between the structure and functions of substances.

Basic concepts: proteins, proteins, proteids, peptide, peptide bond, simple and complex proteins, primary, secondary, tertiary and quaternary protein structures, denaturation.

Learning Tools: Tables on general biology, illustrating the structure of protein molecules; laboratory equipment for laboratory work“Cleavage of hydrogen peroxide using enzymes contained in elodea leaf lashes.”

During the classes

I. Learning new material.

1. The teacher’s story (or a fragment of a lecture) about the structural features of protein molecules as biopolymers consisting of a large number of different amino acids, between which polymerization occurs based on a peptide bond. Sketching and writing on the board and in students’ notebooks.

2. Self-study students of the textbook text (P.42) on the classification of proteins.

3. A conversation about the levels of organization of a protein molecule and the chemical basis of each of the four levels (structures) of this molecule, about denaturation as the loss of a protein molecule of its natural structure.

Structure of a protein molecule.

Protein structure	Characteristic	Communication type	Scheme (students draw independently)
Primary	Linear structure is the sequence of amino acids in a polypeptide chain that determines all other structures of the molecule, as well as the properties and functions of the protein.	Peptide.
Secondary	Twisting a polypeptide chain into a spiral or folding it into an accordion.	Hydrogen bonds.
Tertiary	Globular protein: packaging of secondary structure into a globule; fibrillar protein: several secondary structures arranged in parallel layers, or the twisting of several secondary structures like a rope into a superhelix.	Ionic, hydrogen, disulfide, hydrophobic.
Quaternary	Rarely seen. A complex of several tertiary structures of an organic nature and an inorganic substance, for example, hemoglobin.	Ionic, hydrogen, hydrophobic.

4. The teacher’s story about the variety of functions of proteins with a brief note in notebooks of the essence of functions: structural, enzymatic, transport, protective, regulatory, energy, signaling.

5. Laboratory work “The breakdown of hydrogen peroxide using enzymes contained in leaf cells elodea.”

Progress:

A. Prepare a microscopic specimen of an elodea leaf and examine it under a microscope.
b. Drop a little hydrogen peroxide onto the micropreparation and look again at the state of the elodea leaf cells.
V. Explain what causes the release of bubbles from leaf buds, what kind of gas it is, what substances hydrogen peroxide can break down into, what enzymes are involved in this process?
d. Place a drop of peroxide on a glass slide and, examining it under a microscope, describe the observed picture. Compare the state of hydrogen peroxide in the elodea leaf and on the glass and draw conclusions.

Upon completion of laboratory work, a conversation should be held about biochemical reactions that occur with the participation of protein catalysts-enzymes as the basis for the life of cells and organisms.

The chemical properties of proteins are determined by their different amino acid composition. There are proteins that are highly soluble in water and completely insoluble, chemically active and resistant to various agents, capable of shortening and stretching, etc.

Influenced various factors– high temperature, exposure to chemicals, irradiation, mechanical impact – destruction of the structures of the protein molecule can occur. Violation of the natural structure of a protein is called denaturation. If the impact of the listed factors was short-lived and not strong, then the protein can return to its natural structure - reversible denaturation (renaturation), but if the impact was long or strong, then not only the tertiary and secondary structures are damaged, but also the primary one - irreversible denaturation (Fig. 3).

Functions of proteins.

Function	Characteristic
1. Construction (structural).	They are part of cell membranes and cell organelles (lipoproteins and glycoproteins), participate in the formation of the walls of blood vessels, cartilage, tendons (collagen) and hair (keratin).
2. Motor	It is provided by contractile proteins (actin and myosin), which determine the movement of cilia and flagella, muscle contraction, movement of chromosomes during cell division, and movement of plant organs.
3. Transport.	Many chemical compounds bind and are transported through the bloodstream, for example, hemoglobin and myoglobin transport oxygen, blood serum proteins transport hormones, lipids and fatty acids, and various biologically active substances.
4. Protective.	The production of antibodies (immunoglobulins) in response to the penetration of foreign substances (antigens), which provide immunological protection; participation in blood clotting processes (fibrinogen and prothrombin).
5, Signal (receptor).	Reception of signals from the external environment and transmission of commands into the cell by changing the tertiary structure of proteins embedded in the membrane in response to the action of environmental factors. For example, glycoproteins (built into glycocal X), opsin (a component of the light-sensitive pigments rhodopsin and iodopsin), phytochrome (a light-sensitive plant protein).
6. Regulatory.	Proteins-hormones influence metabolism, i.e. they ensure homeostasis, regulate growth, reproduction, development and other vital processes. For example, insulin regulates blood glucose levels, thyroxine regulates physical and mental development etc.
7. Catalytic (enzymatic).	Enzyme proteins accelerate biochemical processes in the cell.
K. Storage	Animal reserve proteins: albumin (eggs) stores water, ferritin - iron in the cells of the liver and spleen; myoglobin - oxygen in muscle fibers, casein (milk) and seed proteins - a source of nutrition for the embryo.
9. Food (the main source of amino acids).	Food proteins are the main source of amino acids (especially essential ones) for animals and humans; Casein (milk protein) is the main source of amino acids for baby mammals.
10. Energy.	They are a source of energy - the oxidation of 1 g of protein releases 17.6 kJ of energy, but the body uses proteins as a source of energy very rarely, for example, during prolonged fasting.

Enzymes are specific proteins that are present in all living organisms and play the role of biological catalysts.

Chemical reactions in a living cell occur at moderate temperature, normal pressure and a neutral environment. Under such conditions, reactions of synthesis or decomposition of substances would proceed very slowly if they were not exposed to enzymes. Enzymes speed up a reaction without changing its overall outcome by lowering the activation energy. This means that in their presence, significantly less energy is required to make the molecules that react react. Enzymes differ from chemical catalysts in their high degree of specificity, i.e. an enzyme catalyzes only one reaction or acts on only one type of bond. The rate of enzymatic reactions depends on many factors - the nature and concentration of the enzyme and substrate, temperature, pressure, acidity of the medium, the presence of inhibitors, etc.

Classification of enzymes.

Group	Catalyzed reactions, examples
Oxidoreductases.	Redox reactions: the transfer of hydrogen (H) and oxygen (O) atoms or electrons from one substance to another, while the first is oxidized and the second is reduced. Participate in all processes of biological oxidation, for example, inhalation: AN + BA BH (oxidized) or A + O AO (reduced).
Transferases.	Transfer of a group of atoms (methyl, acyl, phosphate or amino group) from one substance to another. For example, the transfer of phosphoric acid residues from ATP to glucose or fructose under the action of phototransferases: ATP + glucose glucose-6-phosphate + ADP.
Hydrolases.	Reactions that break down complex organic compounds into simpler ones by adding water molecules at the site where the chemical bond is broken (hydrolysis). For example, amylase (hydrolyzes starch), lipase (breaks down fats), trypsin (breaks down proteins), etc.: AB + N 2 0 AON + VN.
Lyases	Non-hydrolytic addition to a substrate or detachment of a group of atoms from it. In this case, they may break S-S connections, C-N, C-O, C-S. For example, decarboxylase cleaves off a carboxyl group:
Isomerases	Intramolecular rearrangements, transformation of one isomer into another (isomerization): glucose-6-phosphate glucose-1-phosphate.
Ligases (synthetases)	Reactions of joining two molecules with the formation of new bonds C–O, C–S, C–N, C–C, using the energy of ATP. For example, the enzyme valine-tRNA synthetase, under the action of which the valine-tRNA complex is formed: ATP + valine + tRNA ADP + H 3 P0 4 + valine-tRNA.

The mechanism of action of the enzyme is shown in Fig. 4. Each enzyme molecule has an active center - this is one or more sites in which catalysis occurs due to close contact between the molecules of the enzyme and a specific substance (substrate). The active center is either a functional group (for example, an OH group) or a separate amino acid. The active center can be formed by metal ions, vitamins and other non-protein compounds bound to the enzyme - coenzymes or cofactors. The shape and chemical structure of the active center are such that only certain substrates can bind to it due to their ideal correspondence (complementarity) to each other.

The enzyme molecule changes the globular shape of the substrate molecule. The substrate molecule, when joining the enzyme, also changes its configuration within certain limits to increase the reactivity of the functional groups of the center.

At the final stage of the chemical reaction, the enzyme-substrate complex decomposes to form the final products and free enzyme. The active center released in this case can accept new substrate molecules.

II. A general conversation about the fundamental role of proteins as the most essential chemical compounds for the life and activity of all living things on Earth.

III. Consolidate knowledge during the conversation using the following questions:

1. What organic substances of the cell can be called the most important?
2. How is an infinite variety of proteins created?
3. What are protein biopolymer monomers?
4. How is a peptide bond formed?
5. What is the primary structure of a protein?
6. How does the transition of the primary structure of protein molecules into secondary, and then into tertiary and quaternary?
7. What functions can protein molecules perform?
8. What determines the variety of functions of protein molecules?
9. Give examples of proteins that perform the most different functions. When answering, you can use the following scheme:

Biological functions of proteins.

This is interesting.

Many molecules are very large in both length and molecular weight. Thus, the molecular weight of insulin is 5700, the protein-enzyme ribonuclease is 127 LLC, egg albumin is 36 LLC, hemoglobin is 65 LLC. Different proteins contain a variety of amino acids. A set of all twenty types of amino acids contains: milk casein, muscle myosin and egg albumin. The enzyme protein ribonuclease has 19 amino acids and insulin has 18 amino acids. A team of scientists led by Academician Yu.A. Ovchinnikov managed to decipher the complex structure of the rhodopsin protein, which is responsible for the process of visual perception.

The blood of octopuses, mollusks and spiders is blue because their oxygen carrier is not red hemoglobin, which contains iron atoms, but hemocyanin, which contains copper atoms.

Almost half of the proteins, carbohydrates, 70–80% of vitamins we need, a significant amount of mineral salts, amino acids and other nutrients are contained in bread.

American scientists isolated from a plant (Pentadiplandaceae family) growing in West Africa, a protein that is 2 thousand times sweeter than sugar. This sixth known to science a sweet protein called brazein is found in the fruit, which is eagerly eaten by local monkeys. Biochemists have deciphered the structure of sweet protein molecules; each of them contains 54 amino acid residues.

IV. Homework: Explore § 11, answer the questions on p. 46. ​​Prepare reports or abstracts on the topics: “Proteins are biopolymers of life”, “The functions of proteins are the basis of the life activity of every organism on Earth”, “Denaturation and renaturation, its practical significance”, “Diversity of enzymes, their role in the life of cells and organisms”, etc.

Resources used:

1. Kamensky A.A. General biology 10–11: textbook for general education. institutions. – M.: Bustard, 2006.
2. Kozlova T.A. Thematic and lesson planning in biology for the textbook by A.A. Kamensky and others “General Biology 10–11”. – M.: Publishing house “Exam”, 2006.
3. Biology. General biology. Grades 10–11: workbook to the textbook Kamensky A.A. and others. “General Biology 10–11” – M.: Bustard, 2011.
4. Kirilenko A.A. Molecular biology. Collection of tasks for preparing for the Unified State Exam: levels A, B, C: teaching aid. – Rostov n/d: Legion, 2011.

1. What is the name of the process of disrupting the natural structure of a protein, in which its primary structure is preserved? What factors can lead to disruption of the structure of protein molecules?

The process of disruption of the natural structure of proteins under the influence of any factors without destroying the primary structure is called denaturation. Protein denaturation can be caused by various factors, for example, high temperature, concentrated acids and alkalis, and heavy metals.

2. How do fibrillar proteins differ from globular proteins? Give examples of fibrillar and globular proteins.

Molecules of fibrillar proteins have an elongated, thread-like shape. Globular proteins are characterized by a compact, rounded molecular shape. Fibrillar proteins include, for example, keratin, collagen, myosin. Globular proteins are blood globulins and albumins, fibrinogen, hemoglobin, etc.

3. Name the main biological functions of proteins, give relevant examples.

● Structural function. Proteins are part of all cells and intercellular substance, and are components of various structures of living organisms. For example, in animals, the protein collagen is part of cartilage and tendons, elastin is part of ligaments and the walls of blood vessels, keratin is the most important structural component of feathers, hair, nails, claws, horns, and hooves.

● Enzymatic (catalytic) function. Proteins-enzymes are biological catalysts, accelerating the flow of chemical reactions in living organisms. For example, the digestive enzymes amylase and maltase break down complex carbohydrates into simple ones, pepsin breaks down proteins into peptides, and under the action of lipases, fats are broken down into glycerol and carboxylic acids.

● Transport function. Many proteins are capable of attaching and transporting various substances. For example, hemoglobin binds and transports oxygen and carbon dioxide. Blood albumins transport higher carboxylic acids, and globulins transport metal ions and hormones. Many proteins that make up the cytoplasmic membrane are involved in the transport of substances into and out of the cell.

● Contractile (motor) function. Contractile proteins provide the ability of cells, tissues, organs and entire organisms to change shape and move. For example, actin and myosin ensure muscle function and non-muscle intracellular contractions; tubulin is part of the spindle microtubules, cilia and flagella of eukaryotic cells.

● Regulatory function. Some proteins and peptides are involved in the regulation of various physiological processes. For example, protein-peptide hormones insulin and glucagon regulate blood glucose levels, and somatotropin (growth hormone) regulates the processes of growth and physical development.

● The signaling function lies in the fact that some proteins that are part of the cytoplasmic membrane of cells, in response to the action of external factors, change their spatial configuration, thereby ensuring the reception of signals from the external environment and the transmission of information into the cell. For example, the opsin protein, which is part of the rhodopsin pigment, perceives light and provides visual stimulation to the receptors (rods) of the retina.

● Protective function. Proteins protect the body from the invasion of foreign objects and from damage. For example, immunoglobulins (antibodies) are involved in the immune response, interferon protects the body from viral infection. Fibrinogen, thromboplastin and thrombin ensure blood clotting, preventing blood loss.

● Toxic function. Many living organisms secrete toxin proteins that are poisons to other organisms.

● Energy function. Once broken down into amino acids, proteins can serve as a source of energy in the cell. When 1 g of protein is completely oxidized, 17.6 kJ of energy is released.

● Storage function. For example, special proteins are stored in plant seeds, which are used during germination by the embryo and then by the seedling as a source of nitrogen.

4. What are enzymes? Why would it be impossible for most biochemical processes in a cell to occur without their participation?

Enzymes are proteins that perform the function of biological catalysts, that is, they accelerate the occurrence of chemical reactions in living organisms. They catalyze reactions of synthesis and breakdown of various substances. Without the participation of enzymes, these processes would proceed too slowly or not at all. Almost all life processes of organisms are caused by enzymatic reactions.

5. What is the specificity of enzymes? What is its reason? Why do enzymes function actively only within a certain range of temperature, pH, and other factors?

The specificity of enzymes lies in the fact that each enzyme accelerates only one reaction or acts only on a certain type of bond. This feature is explained by the correspondence of the spatial configuration of the active center of the enzyme to one or another substrate (substrates).

Enzymes are proteins. Changes in pH, temperature, and other factors can cause enzymes to denature, causing them to lose their ability to bind to their substrates.

6. Why are proteins, as a rule, used as energy sources only in extreme cases, when the cells' reserves of carbohydrates and fats are exhausted?

Proteins are the basis of life. They perform extremely important biological functions, many of which (enzymatic, transport, motor, etc.) neither carbohydrates nor fats can perform. Proteins used as an energy substrate provide the same amount of energy as carbohydrates (1 g - 17.6 kJ) and 2.2 times less than fats (1 g - about 39 kJ). In addition, with the complete breakdown of proteins (unlike carbohydrates and fats), not only CO 2 and H 2 O are formed, but also nitrogen and sulfur compounds, some of which are toxic to the body (for example, NH 3). Therefore, the energy function in living organisms is primarily performed by carbohydrates and fats.

7*. In many bacteria, para-aminobenzoic acid (PABA) is involved in the synthesis of substances necessary for normal growth and reproduction. At the same time, sulfonamides, substances similar in structure to PABA, are used in medicine to treat a number of bacterial infections. What do you think is the basis for the therapeutic effect of sulfonamides?

With the help of an enzyme (dihydropteroate synthetase), bacteria convert PABA into a product (dihydropteroic acid), which is then used to synthesize the necessary growth factors. Due to their structural similarity to PABA, sulfonamides are also able to bind to the active site of this enzyme, blocking its work (i.e., competitive inhibition is observed). This leads to disruption of the synthesis of growth factors and nucleic acids in bacteria.

*Tasks marked with an asterisk require students to put forward various hypotheses. Therefore, when marking, the teacher should focus not only on the answer given here, but take into account each hypothesis, assessing the biological thinking of students, the logic of their reasoning, the originality of ideas, etc. After this, it is advisable to familiarize students with the answer given.

The work and functions of proteins underlie the structure of any organism and all life reactions occurring in it. Any disruption of these proteins leads to changes in our well-being and health. The need to study the structure, properties and types of proteins lies in the diversity of their functions.

F. Engels’ definition “Life is a way of existence of protein bodies” still, after a century and a half, has not lost its correctness and relevance.

Structural function

Connective tissue substance and intercellular matrix form proteins collagen , elastin, keratin, proteoglycans .
Directly involved in the construction of membranes and the cytoskeleton (integral, semi-integral and surface proteins) – spectrin(surface, main protein of the cytoskeleton of erythrocytes), glycophorin(integral, fixes spectrin on the surface).
This function includes participation in the creation of organelles - ribosomes.

Enzymatic function

All enzymes are proteins.

At the same time, there is evidence of the existence ribozymes, i.e. ribonucleic acids with catalytic activity.

Hormonal function

Hormones regulate and coordinate metabolism in different cells of the body. Hormones such as insulin And glucagon are proteins, all pituitary hormones are peptides or small proteins.

Receptor function

This function is to selectively bind hormones, biologically active substances and mediators on the surface of membranes or inside cells.

Transport function

Only proteins transport substances in blood, For example, lipoproteins(fat transfer) hemoglobin(oxygen transport), haptoglobin (heme transport), transferrin(iron transport). Proteins transport calcium, magnesium, iron, copper and other ions in the blood.

Transport of substances through membranes carry out proteins - Na + ,K + -ATPase(anti-directional transmembrane transport of sodium and potassium ions), Ca 2+ -ATPase(pumping calcium ions out of the cell), glucose transporters.

Reserve function

An example of stored protein is the production and accumulation in the egg egg albumin.
Animals and humans do not have such specialized depots, but during prolonged fasting, proteins are used muscles, lymphoid organs, epithelial tissues And liver.

Contractile function

There are a number of intracellular proteins designed to change the shape of the cell and the movement of the cell itself or its organelles ( tubulin, actin, myosin).

Protective function

The protective function, preventing the infectious process and maintaining the body’s stability, is performed by immunoglobulins blood, system factors complement(properdin), in case of tissue damage they work coagulation proteins blood - for example, fibrinogen, prothrombin, antihemophilic globulin. Mechanical protection in the form of mucous membranes and skin is provided by collagen and proteoglycans .

This function also includes maintaining consistency colloid osmotic blood pressure, interstitium and intracellular spaces, as well as other functions of blood proteins.

The protein buffer system is involved in the regulation acid-base state .

There are proteins that are the subject of special study:

Monellin– isolated from an African plant, has a very sweet taste, is non-toxic and does not contribute to obesity.

Resilin– has almost perfect elasticity, forms “hinges” at the attachment points of insect wings.

Proteins with properties antifreeze found in Antarctic fish, they protect blood from freezing

• Forward >

Continuation. See No. 11, 12, 13, 14/2005

Biology lessons in science classes

Advanced planning, grade 10

III. Consolidation of knowledge

Filling out the table “Levels of protein organization.”

Table 5. Levels of protein organization

Organization level	Signs	Connections involved in the formation of the structure
Primary	Linear sequence of amino acids in a polypeptide chain	Covalent (peptide) bonds between the carboxyl group residue of one amino acid and the amino group residue of another amino acid
Secondary	Helix, -structure or helices with parameters other than -helices	Hydrogen bonds between the residues of the carboxyl group of one amino acid and the residue of the amino group of another, four amino acid residues distant from the first; in the -structure, hydrogen bonds between the residues of carboxyl and amino groups of one chain and the residues of groups of the same name on the other chain; in spirals - similar to -spirals, but the distance between the turns is different
Tertiary	A globule formed as a result of compact folding of an α-helix; -structures laid in parallel layers; supercoil – several helices twisted together	Ionic, disulfide bridges, hydrophobic, hydrogen
Quaternary	An aggregate of several globules. Characteristic only of proteins with a particularly complex structure	Mainly intermolecular attractive forces, to a lesser extent - hydrogen, ionic and covalent forces

IV. Homework

Study the textbook paragraph (proteins, their content in living matter, structure and properties of amino acids, formation of peptides, levels of protein organization, classification of proteins).

Lesson 10–11. Biological functions of proteins

Equipment: tables on general biology, diagrams and drawings illustrating the structure of proteins, protein classification scheme.

I. Test of knowledge

Working with cards

Card 1. A young biochemist, determining the nitrogen content in a pure protein preparation, received a value of 39.9%. How can you comment on this result?

Card 2. The protein hemoglobin is found in humans in two variants:

blood hemoglobin healthy person(... val-lay-ley-tre-pro-val-glu-liz...);

hemoglobin in the blood of a patient with sickle cell anemia (...val-lay-lay-tre-pro-glu-glu-liz...). What causes the disease?

Card 3. How to determine the number of possible amino acids in a protein based on molecular weight? What determines the possible error of this estimate?

Card 4. How many variants of polypeptide chains can there exist, including 20 amino acids and consisting of 50 amino acid residues? Out of 200 leftovers?

Card 5. Fill in the blanks in the text: “As a result of the interaction of various... and the formation of... bonds, a spiralized protein molecule forms... a structure, which, in turn, depends on... the structure of the protein, that is, on.. amino acids in a polypeptide molecule. The subunits of some proteins form... a structure. An example of such a protein is...”

Card 6. Ions of heavy metals (mercury, lead) and arsenic easily bind to sulfide groups of proteins. Knowing the properties of sulfides of these metals, explain what will happen to the protein when combined with these metals. Why are heavy metals poisons for the body?

1. Proteins, their content in living matter, molecular weight.

2. Proteins are non-periodic polymers. Structure and properties of amino acids. Peptide formation.

3. Primary and secondary structures of the protein molecule.

4. Tertiary and quaternary protein structures.

5. Classification of proteins.

II. Learning new material

1. Denaturation and other properties of proteins

Proteins are extremely diverse in their physical and chemical properties. What is the reason for this? ( Conversation.) Let us give examples of the diversity of properties of proteins.

1. There are proteins that are soluble (for example, fibrinogen) and insoluble (for example, fibrin) in water.

2. There are proteins that are very stable (for example, keratin) and unstable (for example, the enzyme catalase with an easily changing structure).

3. Proteins have a variety of molecular forms - from filaments (myosin - muscle fiber protein) to balls (hemoglobin), etc.

But the structure and properties of a protein always correspond to the function it performs.

At the core most important property All living systems - irritability, lies in the ability of proteins to reversibly change their structure in response to the action of physical and chemical factors. Since the secondary, tertiary and quaternary structures of a protein are created by generally weaker bonds than the primary, they are less stable. For example, when heated, they are easily destroyed. Moreover, although the protein retains its primary structure intact, it cannot perform its biological functions and becomes inactive. The process of destruction of the natural conformation of a protein, accompanied by loss of activity, is called denaturation. Breaking of some weak bonds, changes in conformation and properties also occur under the influence of physiological factors (for example, under the influence of hormones). In this way, the properties of proteins - enzymes, receptors, transporters - are regulated.

These structural changes are usually easily reversible. The reverse process of denaturation is called renaturation. This property of proteins is widely used in the medical and food industries for the preparation of certain medical products, such as antibiotics, vaccines, serums, enzymes; to obtain food concentrates that retain their nutritional properties for a long time in dried form.

If restoration of the spatial configuration of the protein is impossible, then denaturation is considered irreversible. This usually occurs when a large number of bonds are broken, for example when boiling eggs.

Thus, proteins have a complex structure, various shapes and composition. This makes their properties diverse. This, in turn, allows proteins to perform numerous biological functions.

2. Biological functions of proteins

Proteins perform a number of important functions in the cell and body, the main ones of which are the following.

1. Structural (construction). Proteins are part of all cell membranes and cell organelles, as well as extracellular structures. An example of a protein that performs a structural function is keratin. This protein consists of hair, wool, horns, hooves, and the upper dead layer of skin. In the deeper layers of the skin there are pads of proteins collagen And elastin. It is these proteins that provide the strength and elasticity of the skin. They are also contained in ligaments that connect muscles to joints and joints to each other.

2. Enzymatic. Proteins are biological catalysts. For example, pepsin, trypsin, etc. (we will look at the properties of enzyme proteins in detail in the following lessons).

3. Motor. Special contractile proteins are involved in all types of cell and body movement: the formation of pseudopodia, the flickering of cilia and the beating of flagella in protozoa, muscle contraction in multicellular animals, leaf movement in plants, etc. Thus, muscle contraction is provided by muscle proteins actin And myosin, they also make it possible for the amoeba to crawl.

4. Transport. In the blood, in the external cell membranes, there are various transport proteins in the cytoplasm and nuclei of cells. There are transporter proteins in the blood that recognize and bind certain hormones and carry them to target cells. The outer cell membranes contain transporter proteins that provide active and strictly selective transport of sugars, amino acids, and various ions into and out of the cell. Other transport proteins are also known, for example hemoglobin And hemocyanin, carrying oxygen, and myoglobin, which retains oxygen in the muscles.

5. Protective. In response to the penetration of foreign proteins or microorganisms with antigenic properties into the body, blood lymphocytes form special proteins - antibodies that can bind and neutralize them. Saliva and tears contain protein lysozyme– an enzyme that destroys bacterial cell walls. If a microbe gets on the mucous membrane of the eyes or oral cavity, its shell is destroyed by the action of lysozyme, and then protective cells can easily cope with it. Fibrin And thrombin help stop bleeding.

6. Energy (nutritional). Proteins can be broken down, oxidized and provide the energy needed for life. True, this is not very profitable: the energy value of proteins compared to fats is low and amounts to 17.6 kJ (4.1 kcal) energy per 1 g of protein. Typically, proteins are used for energy needs in extreme cases, when reserves of fats and carbohydrates are exhausted.

7. Regulatory. Many (though not all) hormones are proteins - for example, all the hormones of the pituitary gland, hypothalamus, pancreas ( insulin, glucagon) etc. Hormones act on the cell by binding to specific receptors. Each receptor recognizes only one hormone. The receptors for all hormones are proteins. Another example is proteins that regulate the formation and growth of individual organs and tissues during the development of the organism from the zygote. Phytochrome plants is a complex light-sensitive protein that regulates the photoperiodic response in plants.

8. Signal (receptor). The surface membrane of the cell contains embedded protein molecules that can change their tertiary structure in response to environmental factors. This is how signals are received from the external environment and commands are transmitted to the cell.

9. Storage. Thanks to proteins, certain substances can be stored in the body. Egg albumin serves as a water-storing protein in egg whites, milk casein is a source of energy, and protein ferritin retains iron in egg yolk, spleen and liver.

10. Toxic. Some proteins are toxins: cobra venom contains neurotoxin.

III. Consolidation of knowledge

Summarizing conversation while learning new material.

IV. Homework

Study the textbook paragraph (properties of proteins and their biological functions).

Lesson 12–13. Enzymes, their chemical composition and structure. Biological role of enzymes

Equipment: tables on general biology, diagrams and drawings illustrating the structure and mechanism of action of enzymes, a classification scheme for enzymes, equipment for laboratory work.

I. Test of knowledge

Working with cards

Card 1. It has been established that with sufficient caloric content of food, but in the absence of protein in it, pathological phenomena are observed in animals: growth stops, blood composition changes, etc. What is this connected with?

Card 2. Why are proteins called “carriers and organizers of life”?

Card 3. What structural features of a protein molecule enable it to perform many functions, for example transport, protective, energy?

Card 4. Fill in the blanks in the text: “Protective proteins are called... . They bind to..., entering the body and called.... Among thousands of different proteins... they recognize only one... and react with it. This mechanism of resistance to pathogens is called...”

Card 5. What similar functions do proteins, carbohydrates and lipids perform in living organisms?

Oral knowledge test on questions

1. Denaturation and other properties of proteins. Relationship between the structure, properties and functions of proteins.

2. Biological functions of proteins ( three students).

II. Learning new material

1. Enzymes and their importance in life processes

From your chemistry course you know what a catalyst is. This is a substance that speeds up a reaction, remaining unchanged at the end of the reaction (without being consumed). Biological catalysts are called enzymes(from lat. fermentum– fermentation, sourdough), or enzymes.

Almost all enzymes are proteins (but not all proteins are enzymes!). IN last years It became known that some RNA molecules also have the properties of enzymes.

The highly purified crystalline enzyme was first isolated in 1926 by the American biochemist J. Sumner. This enzyme was urease, which catalyzes the breakdown of urea. To date, more than 2 thousand enzymes are known, and their number continues to grow. Many of them are isolated from living cells and obtained in their pure form.

Thousands of reactions are constantly going on in the cell. If you mix organic and inorganic substances in a test tube in exactly the same proportions as in a living cell, but without enzymes, then almost no reactions will occur at a noticeable speed. It is thanks to enzymes that genetic information is realized and all metabolism is carried out.

The name of most enzymes is characterized by the suffix -ase, which is most often added to the name of the substrate - the substance with which the enzyme interacts.

2. Structure of enzymes

Compared to the molecular weight of the substrate, enzymes have a much larger mass. This discrepancy suggests that not the entire enzyme molecule is involved in catalysis. To understand this issue, you need to get acquainted with the structure of enzymes.

By structure, enzymes can be simple or complex proteins. In the second case, the enzyme contains, in addition to the protein part ( apoenzyme) there is an additional group of non-protein nature - an activator ( cofactor, or coenzyme), resulting in the formation of active holoenzyme. Enzyme activators are:

1) inorganic ions (for example, to activate the amylase enzyme found in saliva, chloride ions (Cl–) are required);

2) prosthetic groups (FAD, biotin) tightly bound to the substrate;

3) coenzymes (NAD, NADP, coenzyme A), loosely associated with the substrate.

The protein part and the non-protein component individually lack enzymatic activity, but when combined together they acquire the characteristic properties of an enzyme.

The protein part of enzymes contains active centers that are unique in their structure, which are a combination of certain amino acid residues strictly oriented in relation to each other (the structure of the active centers of a number of enzymes has now been deciphered). The active center interacts with the substrate molecule to form an “enzyme-substrate complex.” The "enzyme-substrate complex" then breaks down into the enzyme and the product or products of the reaction.

According to the hypothesis put forward in 1890 by E. Fisher, the substrate approaches the enzyme as key to the lock, i.e. the spatial configurations of the active site of the enzyme and the substrate correspond exactly ( complementary) each other. The substrate is compared to a “key” that fits the “lock” - the enzyme. Thus, the active center of lysozyme (the enzyme of saliva) has the appearance of a slit and in shape exactly corresponds to a fragment of a complex carbohydrate molecule of a bacterial bacillus, which is broken down under the action of this enzyme.

In 1959, D. Koshland put forward a hypothesis according to which the spatial correspondence of the structure of the substrate and the active center of the enzyme is created only at the moment of their interaction with each other. This hypothesis was called "hands and gloves" hypothesis(induced interaction hypothesis). This process of “dynamic recognition” is the most widely accepted hypothesis today.

3. Differences between enzymes and non-biological catalysts

Enzymes differ from non-biological catalysts in many ways.

1. Enzymes are much more efficient (10 4 –10 9 times). Thus, a single molecule of the catalase enzyme can break down 10 thousand molecules of hydrogen peroxide, which is toxic to cells, in one second:

2H 2 O 2 ––> 2H 2 O + O 2,

which occurs during the oxidation of various compounds in the body. Or another example confirming the high efficiency of enzymes: at room temperature, one urease molecule is capable of breaking down up to 30 thousand urea molecules in one second:

H 2 N–CO–NH 2 + H 2 O ––> CO 2 + 2NH 3.

Without a catalyst, this would have taken about 3 million years.

2. High specificity of enzyme action. Most enzymes act on only one or a very small number of “their” natural compounds (substrates). The specificity of enzymes is reflected by the formula "one enzyme - one substrate". Due to this, in living organisms many reactions are catalyzed independently.

3. Enzymes are subject to fine and precise regulation. The activity of an enzyme can increase or decrease with slight changes in the conditions in which it “works.”

4. Non-biological catalysts in most cases only work well at high temperatures. Enzymes, being present in cells in small quantities, work at normal temperature and pressure (although the scope of action of enzymes is limited, since high temperature causes denaturation). Since most enzymes are proteins, their activity is highest when physiologically normal conditions: t=35–45 °C; slightly alkaline environment (although each enzyme has its own optimal pH value).

5. Enzymes form complexes - so-called biological conveyors. The process of breakdown or synthesis of any substance in a cell is usually divided into a number of chemical operations. Each operation is performed by a separate enzyme. A group of such enzymes constitutes a kind of biochemical conveyor belt.

6. Enzymes are capable of being regulated, i.e. “turn on” and “turn off” (however, this does not apply to all enzymes; for example, salivary amylase and a number of other digestive enzymes are not regulated). In most apoenzyme molecules there are sections that also recognize the final product that “comes off” the multienzyme conveyor. If there is too much of such a product, then the activity of the initial enzyme itself is inhibited by it, and vice versa, if there is not enough product, then the enzyme is activated. This is how many biochemical processes are regulated.

Thus, enzymes have a number of advantages over non-biological catalysts.

4. Mechanism of action of enzymes

Enzymes operate in living organisms according to the same laws as any catalysts. Enzyme catalysis is based on reducing the energy barrier (the so-called activation energy) due to the formation of intermediate complexes of the enzyme with the substrate. In the absence, for example, of amylase, the reaction between starch and water does not occur because the molecules do not have sufficient energy for this purpose. The enzyme speeds up the chemical process because in its presence, less energy is required to “start” a given reaction. Let us consider the mechanism of action of enzymes in more detail.

1. By catalyzing a reaction, the enzyme brings the molecules of “its” substrates closely together, so that those parts of the molecules that are to react are nearby.

2. The substrate, having joined the enzyme, changes somewhat. The enzyme can attract electrons, causing tension to occur in some of the bonds of the substrate molecule. This in turn increases reactivity molecules, since the bonds between atoms are weakened and they are released more easily (this is how the enzyme is assumed to speed up the reaction).

3. The enzyme “rips off” an atom (or atoms) from each of the substrates, after which the substrates are combined.

4. The separated atoms combine with each other and leave the enzyme. Now the enzyme is able to attach new molecules of substrates.

Most often, enzymes are confined to specific cellular structures. They retain their properties outside the body. Enzymes are successfully used in the baking, brewing, winemaking, leather, and chemical industries.

5. Classification of enzymes

Students work with the text of the textbook and fill out the table “The most important groups of enzymes” with subsequent checking.

Table 6. The most important groups of enzymes

Number and name of classes	Catalyzed reactions
1. Oxidoreductases 2. Transferases 3. Hydrolases 4. Lyases 5. Isomerases 6. Ligases (synthetases)	Redox reactions: transfer of hydrogen or oxygen atoms or electrons from one substance to another Transfer of functional groups from one substance to another Hydrolysis: reactions that break down complex organic matter to simpler ones by adding water Non-hydrolytic addition or elimination of functional groups Isomerization, i.e. conversion of isomers into each other Synthesis reactions using ATP energy	Catalase decomposes hydrogen peroxide into water and molecular oxygen; cytochromes transfer and attach electrons to oxygen atoms during respiration and to protons during the reactions of the light phase of photosynthesis Under the action of phosphotransferases, phosphoric acid residues are transferred from ATP to glucose or fructose Amylase hydrolyzes starch to maltose; trypsin hydrolyzes proteins and peptides to amino acids Elimination of carboxyl groups by decarboxylases Interconversions of glucose and fructose in plants under the action of glucose phosphate isomerase Carboxylases catalyze the addition carbon dioxide to organic acids

III. Consolidation of knowledge

Laboratory work No. 1. “Study of the catalytic activity of the enzyme catalase in living tissues”

Equipment: tripods, test tubes, bottles with a fresh 3% solution of hydrogen peroxide, plant and animal tissues, jars with water and elodea, microscopes, slides and cover glasses, tweezers and pipettes.

Progress

1. Pour 2 ml of hydrogen peroxide into test tubes containing raw meat, cooked meat, raw and boiled potatoes. Explain the phenomena you observe during the action of peroxide on living and dead tissues.

2. Place an Elodea leaf on a glass slide in a drop of water and examine under a microscope at low magnification the place where the leaf is torn from the stem.

3. Apply two drops of hydrogen peroxide to an elodea leaf, cover with a cover slip and examine under a microscope where the leaf is torn from the stem. Explain the rapid release of gas bubbles from damaged cells of the Elodea leaf.

4. Conclusions.

How does enzyme activity manifest itself in living and dead tissues? Why?

Does enzyme activity differ in living tissues of plants and animals?

How would you propose to measure the rate of decomposition of hydrogen peroxide?

Do you think all living organisms contain the enzyme catalase, which ensures the decomposition of hydrogen peroxide? Justify your answer.

IV. Homework

Study the textbook paragraph (enzymes, their meaning, structure, mechanism of action and classification).

Lesson 14–15. Nucleic acids are non-periodic polymers. Nucleotide structure. Formation of polynucleotides. Formation of a double-stranded DNA molecule. Principle of complementarity

Equipment: tables on general biology, diagrams and drawings illustrating the structure and mechanism of action of enzymes, a classification scheme for enzymes, a diagram of the structure of a nucleotide, a model of the structure of DNA.

I. Test of knowledge

Working with cards

Card 1. It is known that the rate of chemical reactions decreases by only 2–3 times when the temperature decreases by 10 °C. For greater stability of analyzed samples, biochemists store them at a low temperature. However, if a freezing person’s body temperature drops by at least 10 °C, this leads to serious, often irreversible consequences. Is there a contradiction here?

Card 2. From notebooks Kifa Mokievich: “Protease is an enzyme that breaks down peptide bonds in proteins. Amylase is an enzyme that breaks down glycosidic bonds in carbohydrates. It is known that all enzymes have extremely high specificity and fit the substrate like a key to a lock. Since the substrates of the enzymes are the same, then the enzymes themselves are the same. It follows that biochemists only need to study one amylase (say, from human saliva) and one protease (say, from washing powder) - after all, they are identical!” How could you object to Kifa Mokievich?

Card 3. A certain enzyme was isolated from rat tissue. Its solution at +4 °C retains catalytic activity for several weeks. After it was placed in a thermostat at +40 °C for 2 hours, it lost 50% of its activity. Is it true that after another 2 hours it would have become completely inactive? But in the body of a rat it is by no means +4 °C, but just +40 °C. So does she need such an unstable enzyme?

Card 4. Try to make a list of enzymes necessary for the existence of any cell. If you do not know the name of an enzyme, it is enough to indicate the reaction it catalyzes.

Card 5. An experimenter, studying the rate of protein breakdown by protease, discovered that over time it first increased several times, and then fell - until the enzyme activity was completely lost. How can this pattern be explained? Which proteases do you think have this property?

Card 6. Why might enzyme activity depend on pH?

Card 7. In what ways can a cell control the speed of chemical processes occurring in it? In what ways can the human body regulate the speed of chemical processes?

Card 8. How do you understand “catalytic (enzymatic) conveyor belt in a cell”? What is the advantage of a conveyor arrangement of enzyme molecules on a membrane compared to their free, random position in the cytoplasm?

Oral knowledge test on questions

1. Enzymes and their importance in life processes.

2. The structure of enzymes and the reason for their high specificity.

3. Differences between enzymes and non-biological catalysts.

4. Mechanism of action of enzymes.

5. Classification of enzymes.

II. Learning new material

1. Nucleic acids, their content in the cell, molecular sizes and molecular weight

Nucleic acids are natural high molecular weight organic compounds, polynucleotides that ensure the storage and transmission of hereditary (genetic) information in living organisms.

These organic compounds were discovered in 1869 by the Swiss physician I.F. Miescher in cells rich in nuclear material (leukocytes, salmon sperm). Nucleic acids are integral part cell nuclei, which is why they received such a name (from lat. nucleus- core). In addition to the nucleus, nucleic acids are also found in the cytoplasm, centrioles, mitochondria, and chloroplasts.

There are two types of nucleic acids in nature: deoxyribonucleic acids (DNA) and ribonucleic acids (RNA). They differ in composition, structure and functions. DNA is a double-stranded molecule, while RNA is single-stranded. The content of nucleic acids in living matter is from 1 to 2%.

Nucleic acids are biopolymers that reach enormous sizes. The length of their molecules is hundreds of thousands of nanometers (1 nm = 10–9 m), which is thousands of times longer than the length of protein molecules. The DNA molecule is especially large. Molecular mass of nucleic acids reaches tens of millions and billions (10 5 –10 9). For example, the DNA mass of Escherichia coli is 2.5x109, and in the nucleus of a human germ cell (haploid set of chromosomes) the length of DNA molecules is 102 cm.

2. NC – non-periodic polymers. Types of nucleotides and their structure

Nucleic acids are non-periodic biopolymers, the polymer chains of which are formed by monomers called nucleotides. DNA and RNA molecules contain four types of nucleotides. DNA nucleotides are called deoxyribonucleotides, and RNA - ribonucleotides. The nucleotide composition of DNA and RNA is reflected in the table.

Table 7. Composition of DNA and RNA nucleotides

Let's look at the structure of a nucleotide. Nucleotides are complex organic compounds that include three components. The diagram of the structure of a DNA nucleotide is shown in the figure.

1. Nitrogenous bases have a cyclic structure, which, along with carbon atoms, includes atoms of other elements, in particular nitrogen. Due to the presence of nitrogen atoms in these compounds, they are called “nitrogenous”, and since they have alkaline properties, they are called “bases”. The nitrogenous bases of nucleic acids belong to the classes of pyrimidines and purines. Pyrimidine bases are derivatives of pyrimidine, which has one ring in its molecule. Pyrimidine bases are found in deoxyribonucleotides thymine And cytosine, and in the composition of ribonucleotides - cytosine And uracil. Uracil differs from thymine in the absence of a methyl group (–CH 3).

Purine bases are derivatives of purine, which has two rings. Purine bases include adenine And guanine. They are part of the nucleotides of both DNA and RNA.

2. Carbohydrate – pentose (C 5 ). This component also takes part in the formation of nucleotides. DNA nucleotides contain pentose - deoxyribose, and RNA nucleotides - ribose. The carbohydrate composition of nucleotides is reflected, as we see, in the names of nucleic acids: deoxyribonucleic and ribonucleic. Pentose compounds with a nitrogenous base are called “nucleosides.”

3. Phosphoric acid residue. Phosphate imparts acidic properties to nucleic acids.

So, a nucleotide consists of a nitrogenous base, pentose and phosphate. In the composition of nucleotides, on the one hand, a nitrogenous base is attached to the carbohydrate, and on the other, a phosphoric acid residue.

To be continued