Abstract prepared

Student 10 "A" class

Pavelchuk Vladislav

INTRODUCTION
Proteins, together with nucleic acids, lipids, carbohydrates, some low-molecular organic substances, mineral salts and water, form the protoplasm of all terrestrial organisms - animals and plants, complex and elementary. The term “protoplasm” was proposed by the Czech physiologist Purkynė (1839) to designate the contents of a living cell. The protein content in protoplasm, as a rule, is significantly higher than all its other components (not counting water). In most cases, proteins account for up to 75-80% of the dry mass of cells.
Protein substances represent the main, most active part of protoplasm: “In protoplasm, the properties of the component that is present in larger quantities and which is most active shine through more clearly” Danilevsky A. Ya. (the main substance of protoplasm and its modification by life. 1894).
The conviction in the first-rate importance of proteins for life remains unshaken in our time, despite the discovery of the role of nucleic acids in the phenomena of heredity, the clarification of the critical importance of vitamins, hormones, etc. for life.
Due to the peculiarities of their composition and structure, proteins exhibit a remarkable variety of physical and chemical properties. There are known proteins that are completely insoluble in water; there are proteins that are extremely unstable, changing under the influence of visible light or even light mechanical touch. There are proteins whose molecules have the form of threads reaching a length of several millimeters, and there are proteins whose molecules are balls with a diameter of several tens of angremes. But in all cases, the structure and properties of proteins are in close and responsive connection with the function they perform.
I. Structure of proteins.
Proteins are the largest and most diverse class of organic compounds in the cell. Proteins are biological heteropolymers whose monomers are amino acids. all amino acids have at least one amino group (-NH2) and a carboxyl group (-COOH) and differ in the structural and physicochemical properties of radicals ®.
Peptides containing from several amino acid residues to several dozen exist in the body in free form and have high biological activity. These include a number of hormones (oxytocin, adrenocorticotropic hormone), some very toxic toxic substances (for example, amanitin of mushrooms), as well as many antibiotics produced by microorganisms.
Proteins are high molecular weight polypeptides containing from one hundred to several thousand amino acids.
II. CLASSIFICATION OF PROTEINS
Proteins are divided into proteins (simple proteins), consisting only of amino acid residues, and proteids (complex proteins), which upon hydrolysis yield amino acids and substances of a non-protein nature (phosphoric acid, carbohydrates, heterocyclic compounds, nucleic acids). Proteins and proteids are divided into a number of subgroups.
Proteins
Albumins are proteins with a relatively small molecular weight and are highly soluble in water. They are salted out from aqueous solutions with a saturated ammonium sulfate solution and coagulated (denatured) when heated. Egg white is a typical representative of albumin. Many of them are obtained in a crystalline state.
Globulins are proteins that are insoluble in pure water, but soluble in a warm 10% NaCl solution. Pure globulin is extracted by diluting the saline solution with plenty of water. Globulin is the most common protein found in muscle fibers, blood, milk, eggs, and plant seeds.
Prolamines are slightly soluble in water. Dissolves in 60-80% aqueous ethyl alcohol. When prolamines are hydrolyzed, the amino acid proline is formed in large quantities. Characteristic of cereal seeds. An example of this is gliadin, the main protein in wheat gluten.
Glutelins are soluble only in 0.2% alkali. Found in the seeds of wheat, rice, and corn.
Protamines are found only in fish milk. They are 80% alkaline amino acids, making them strong bases. Completely free of sulfur.
Scleroproteins are insoluble proteins that have a filamentous (fibrillar) molecular shape. Contains sulfur. These include collagen (proteins of cartilage, some bones), elastin (proteins of tendons, connective tissues), keratin (proteins of hair, horns, hooves, upper layer of skin), fibroin (protein of raw silk threads).
Proteids. Complex proteins are divided into groups depending on the composition of their non-protein part, which is called the prosthetic group. The protein part of complex proteins is called apoprotein.
Lipoproteins - hydrolyze into simple protein and lipids. Lipoproteins are contained in large quantities in the composition of chlorophyll grains and protoplasm of cells and biological membranes.
Glycoproteins - hydrolyze into simple proteins and high molecular weight carbohydrates. Insoluble in water, but soluble in dilute alkalis. Contained in various mucous secretions of animals, in egg whites,
Chromoproteins - hydrolyze into simple proteins and coloring matter. For example, hemoglobin in the blood breaks down into the protein globin and a complex nitrogenous base containing iron.
Nucleoproteins - hydrolyze into simple proteins, usually protamines, or histones, and nucleic acids.
Phosphoproteins - contain phosphoric acid. They play a big role in the nutrition of a young body. An example of this is casein, a milk protein.
III. STRUCTURAL ORGANIZATION OF PROTEIN MOLECULES
Since proteins consist of several dozen amino acids connected into a polypeptide chain, it is energetically unfavorable for the cell to keep them in the form of a chain (the so-called unfolded form). Therefore, proteins undergo compaction and folding, as a result of which they acquire a certain spatial organization - a spatial structure.
There are 4 levels of spatial organization of proteins.
The primary structure is the sequence of amino acids in the polypeptide chain and is determined by the sequence of nucleotides in the section of the DNA molecule that encodes the protein. The primary structure of any protein is unique and determines its shape, properties and functions.
The secondary structure of most proteins has the form of a spiral and arises as a result of the formation of hydrogen bonds between - CO - and NH - groups of different amino acid residues of the polypeptide chain.
The tertiary structure has the form of a coil or globule, and is formed as a result of the complex spatial arrangement of the protein molecule. Each type of protein has a specific globule formula. The strength of the tertiary structure is ensured by the various bonds that arise between amino acid radicals (disulfide, ionic, hydrophobic).
The quaternary structure is a complex complex that combines several tertiary structures (for example, the hemoglobin protein is formed by four globules) held together by non-covalent bonds: ionic, hydrogen and hydrophobic.
A change in the spatial shape, and therefore the properties and biological activity of the native protein, is called denaturation. Denaturation can be reversible or irreversible. In the first case, the quaternary, tertiary or secondary structure is disrupted and the reverse process of restoring the protein structure - renaturation - is possible, in the second case the peptide bonds in the primary structure are broken. Denaturation is caused by chemical influences, high temperature (above 45 degrees C), irradiation, high pressure, etc.
V. EXTRACTION OF PROTEINS
Proteins are extracted from natural materials with water, solutions of salts, alkalis, acids, and aqueous-alcoholic solutions. The product thus obtained usually contains a significant amount of impurities. For further isolation and purification of the protein, the solution is treated with salts (salting out), saturated with alcohol or acetone, and neutralized. In this case, the corresponding protein fraction is released. It is very difficult to isolate a protein in an unchanged state; for this it is necessary to observe a number of conditions: low temperatures, a certain reaction of the environment, etc.
Isolated and purified proteins are in most cases a white powder or retain their natural form (for example, wool and silk proteins).
Based on the shape of their molecules, proteins can be divided into two groups: fibrillar, or filamentous, and globular, or spherical. Fibrillar proteins, as a rule, perform structure-forming functions. Their properties (strength, extensibility) depend on the method of packaging of polypeptide chains, therefore, after isolation, proteins usually retain their natural shape. Examples of fibrillar proteins include silk fibroin, keratins, and collagens.
The second group includes most of the proteins found in the human body. Globular proteins are characterized by the presence of regions with high reactivity (they can be catalytic centers of enzymes) or form complexes with other molecules due to functional groups close to each other in space.
VI. COLOR REACTIONS OF PROTEINS
Proteins are characterized by some color reactions associated with the presence of certain groups and amino acid residues in their molecule.
Biuret reaction - the appearance of a violet color when the protein is treated with a concentrated alkali solution and a saturated CuSO4 solution. Associated with the presence of peptide bonds in the molecule.
Xanthoprotein reaction - the appearance of a yellow color as a result of the action of concentrated nitric acid on proteins. The reaction is associated with the presence of aromatic rings in the protein.
Million reaction - the appearance of a cherry-red color when the protein is exposed to Millon's reagent (a solution of mercuric nitrate in nitrous acid). The reaction is explained by the presence of phenolic groups in the protein.
Sulfhydryl reaction - the formation of a black precipitate of lead sulfide when heating a protein with a plusbit solution (due to the presence of sulfhydryl groups in the protein).
The Adamkiewicz reaction is the appearance of a violet color when glyoxalic and concentrated sulfuric acids are added to the protein. Associated with the presence of indole groups.
VII. DECODING THE PRIMARY STRUCTURE OF A PROTEIN
To decipher the primary structure of a protein means to establish its formula, that is, to determine in what sequence the amino acid residues are located in the polypeptide chain.
Knowledge of the primary structure of the protein is well illustrated by the work of Ingram, who studied the causes of one hereditary blood disease common in some areas of Africa and the Mediterranean, the so-called sickle anemia. Patients with sickle anemia are pale, complain of weakness, shortness of breath at the slightest exertion. They rarely live to be 12-17 years old. A blood test reveals an unusual shape of red blood cells. Red blood cells in patients have the shape of sickles or crescents, while normal red blood cells have the shape of biconcave discs. A detailed study revealed that hemoglobin in healthy red blood cells is distributed evenly and randomly throughout the cell, while in the red blood cells of patients with anemia, hemoglobin forms regular crystalline structures. Due to the crystallization of hemoglobin, red blood cells become deformed. What is the reason for such a significant change in hemoglobin? Ingram isolated hemoglobin from the blood of patients with sickle disease and analyzed its primary structure. It turned out that the difference between the hemoglobin of patients and the hemoglobin of healthy people is only that in the polypeptide chain of hemoglobin of patients in the 6th place (from the N-terminus) there is a valine residue (val), while in the same place in healthy hemoglobin contains glutalic acid (glu). The hemoglobin molecule consists of four subunits (four polypeptide chains - two alpha and two beta with a total number of amino acid residues equal to: 141?2 + 146?2 + 574. The replacement of “glu” with “val” occurs in alpha chains, i.e. That is, in two chains out of four. Thus, in a molecule consisting of 574 amino acid residues, it is enough to replace only two and leave the remaining 572 unchanged in order for profound changes in the properties of hemoglobin to occur. If you change its ability to crystallize and bind oxygen, then. there will be fatal consequences for human health.
Sanger (Cambridge, England) began to decipher the primary structure of the insulin protein back in the 40s. In the course of painstaking and time-consuming research, Sanger developed a number of new methods and techniques of analysis. He carried out this work for more than 10 years and was crowned with complete success: the insulin formula was established, and for his outstanding achievements the author was awarded the Nobel Prize (1958). The significance of Sanger’s work lies not only in deciphering the primary structure of insulin, but also in the fact that experience was gained, new methods were developed, and the reality of these studies was proven. After Sanger's work, this was easier for other researchers to do. Indeed, following Sanger, many laboratories began work on deciphering the primary structure of a number of proteins, improved analysis methods, and developed new methods.
VIII. FUNCTIONS OF PROTEINS
Catalytic
Proteins - enzymes are produced by living organisms; they have a catalytic effect, i.e. the ability to increase the rate of certain chemical reactions. Fermentation processes, which have been used since prehistoric times in the production of wines, vinegar, beer and bread, are based on enzymatic action. In 1680, the Dutch naturalist Antonie Leeuwenhoek used a microscope of his own design to observe yeast and bacterial cells; however, he did not consider them to be living organisms. In 1857, Louis Pasteur showed that yeast is a living organism and fermentation is a physiological process. In 1897, E. Buchner was able to prove that fermentation could occur without the participation of whole yeast cells. By extracting the yeast cells, he obtained a solution that did not contain cells, but had enzymatic activity (containing an enzyme, or enzyme). The word "enzyme" comes from the Greek en 2yme - in leaven.
Until 1926, there was no evidence that enzymes were proteins. Only in 1926, James B. Sumner (1887-1955), who worked at Cornell University, managed to isolate the enzyme urease from soybeans in its pure form and obtain it in crystalline form. Urease is a protein that catalyzes the hydrolytic breakdown of urea.
CO(NH2) 2 + H2O - CO2 + 2NH3
Molecular weight of urease is 480000; the molecule consists of six subunits.
About 2000 different enzymes are known, some of them have been studied in detail. According to modern classification, all enzymes are divided into six classes.
1. Oxyreductases or redox enzymes. This is a large group consisting of 180-190 enzymes. Oxyreductases accelerate the oxidation or reduction of various chemicals. Thus, the enzyme alcohol dehydrogenase belonging to this class catalyzes the oxidation of ethyl alcohol into acetaldehyde and plays an important role in the process of alcoholic fermentation.
The enzyme lipoxygenase oxidizes unsaturated fatty acids with air oxygen. The action of this enzyme is one of the reasons for the rancidity of flour and cereals.
2. Transferases. Representatives of this group of enzymes catalyze the transfer of various groups from one molecule to another, for example, the enzyme tyrosine aminotransferase catalyzes the transfer of an amino group. Enzymes of this group play an important role in medicine.
3. Hydrolases. Enzymes of this group catalyze hydrolysis reactions. Representatives of this group of enzymes are of great importance in digestion processes, in food and other industries. Thus, the enzyme lipase catalyzes the hydrolysis of glycerides with the formation of free fatty acids and glycerol. The hydrolysis of pectin substances occurs with the participation of pectolytic enzymes; their use makes it possible to increase the yield and clarify fruit and berry juices.
A representative of the group of hydrolases are amylases, which catalyze the hydrolysis of starch. They are widely used in the alcohol, baking, starch and syrup industries.
Hydrolases include a large group of proteolytic enzymes that catalyze the hydrolysis of proteins and peptides. They are used in the light and food industries. They are used to “soften” meat, leather, and produce cheeses.
4. Lyases. Catalyze splitting reactions between carbon atoms, carbon and oxygen, carbon and nitrogen, carbon and halogen. Enzymes of this group include decarboxylases, which cleave a molecule of carbon dioxide from organic acids.
etc.................

Lesson type - combined

Methods: partially search, problem presentation, explanatory and illustrative.

Target:

Formation in students of a holistic system of knowledge about living nature, its systemic organization and evolution;

Ability to give a reasoned assessment of new information on biological issues;

Fostering civic responsibility, independence, initiative

Tasks:

Educational: about biological systems (cell, organism, species, ecosystem); history of the development of modern ideas about living nature; outstanding discoveries in biological science; the role of biological science in the formation of the modern natural science picture of the world; methods of scientific knowledge;

Development creative abilities in the process of studying the outstanding achievements of biology that have entered into universal human culture; complex and contradictory ways of developing modern scientific views, ideas, theories, concepts, various hypotheses (about the essence and origin of life, man) in the course of working with various sources of information;

Upbringing conviction in the possibility of learning about living nature, the need to take care of the natural environment and one’s own health; respect for the opponent's opinion when discussing biological problems

Personal results of studying biology:

1. education of Russian civic identity: patriotism, love and respect for the Fatherland, a sense of pride in one’s Motherland; awareness of one's ethnicity; assimilation of humanistic and traditional values ​​of multinational Russian society; fostering a sense of responsibility and duty to the Motherland;

2. the formation of a responsible attitude towards learning, the readiness and ability of students for self-development and self-education based on motivation for learning and knowledge, conscious choice and construction of a further individual educational trajectory based on orientation in the world of professions and professional preferences, taking into account sustainable cognitive interests;

Meta-subject results of teaching biology:

1. the ability to independently determine the goals of one’s learning, set and formulate new goals for oneself in learning and cognitive activity, develop the motives and interests of one’s cognitive activity;

2. mastery of the components of research and project activities, including the ability to see a problem, pose questions, put forward hypotheses;

3. ability to work with different sources of biological information: find biological information in various sources (textbook text, popular scientific literature, biological dictionaries and reference books), analyze and

evaluate information;

Cognitive: identification of essential features of biological objects and processes; providing evidence (argumentation) of the relationship between humans and mammals; relationships between humans and the environment; dependence of human health on the state of the environment; the need to protect the environment; mastering the methods of biological science: observation and description of biological objects and processes; setting up biological experiments and explaining their results.

Regulatory: the ability to independently plan ways to achieve goals, including alternative ones, to consciously choose the most effective ways to solve educational and cognitive problems; the ability to organize educational cooperation and joint activities with the teacher and peers; work individually and in a group: find a common solution and resolve conflicts based on coordinating positions and taking into account interests; formation and development of competence in the field of use of information and communication technologies (hereinafter referred to as ICT competences).

Communicative: the formation of communicative competence in communication and cooperation with peers, understanding the characteristics of gender socialization in adolescence, socially useful, educational and research, creative and other types of activities.

Technologies : Health conservation, problem-based, developmental education, group activities

Techniques: analysis, synthesis, inference, translation of information from one type to another, generalization.

During the classes

Tasks

Reveal the leading role of proteins in the structure and functioning of the cell. ,

Explain the structure of protein macromolecules, which have the nature of informational biopolymers.

To deepen the knowledge of schoolchildren about the connection between the structure of molecules of substances and their functions using the example of proteins.

Basic provisions

The primary structure of the protein is determined by the genotype.

The secondary, tertiary and quaternary structural organization of a protein depends on the primary structure.

All biological catalysts - enzymes - are protein in nature.

4. Protein molecules provide immunological protection of the body from foreign substances .

Issues for discussion

How is the specificity of the activity of biological catalysts determined?

What is the mechanism of action of the precision surface receptor?

Biological polymers - proteins

Among the organic substances of cells, proteins occupy first place both in quantity and in importance. In animals they account for about 50% of the dry mass of the cell. In the human body there are 5 million types of protein mo-, differing not only from each other, but also from proteins of other organisms. Despite such diversity and complexity of structure, they are built from only 20 different amino acids.

Amino acids have a general structural plan, but differ from each other in the structure of the radical (K), which is very diverse. For example, the amino acid alanine has a simple radical - CH3, the cysteine ​​radical contains sulfur - CH28H, other amino acids have more complex radicals.

Proteins isolated from living organisms of animals, plants and microorganisms include several hundred and sometimes thousands of combinations of 20 basic amino acids. The order of their alternation is very diverse, which makes it possible for the existence of a huge number of protein molecules that differ from each other. For example, for a protein consisting of only 20 amino acid residues, about 2 is theoretically possible. 1018 variants of various protein molecules, differing in the alternation of amino acids, and therefore in properties. The sequence of amino acids in a polypeptide chain is usually called the primary structure of a protein.

However, a protein molecule in the form of a chain of amino acid residues sequentially connected to each other by peptide bonds is not yet capable of performing specific functions. This requires a higher structural organization. By forming hydrogen bonds between the residues of carboxyl and amino groups of different amino acids, the protein molecule takes the form of a helix (a-structure) or a folded layer - an “accordion” (P-structure). This is a secondary structure, but it is often not sufficient to acquire characteristic biological activity.

The secondary structure of the protein ((3-structure) is on top. The tertiary structure of the protein is below:

- ionic interactions,

- hydrogen bonds.

- disulfide bonds,

- hydrophobic interactions,

- hydratable groups

Often only a molecule with a tertiary structure can play the role of a catalyst or any other. Tertiary structure is formed due to the interaction of radicals, in particular cysteine ​​amino acid radicals, which contain sulfur. The sulfur atoms of two amino acids located at some distance from each other in the polypeptide chain are connected to form so-called disulfide, or 8-8, bonds. Thanks to these interactions, as well as other, less strong bonds, the protein helix folds and takes on the shape of a ball, or globules. The way polypeptide helices are arranged in a globule is called the tertiary structure of a protein. Many proteins with a tertiary structure can perform their biological role in the cell. However, the implementation of some body functions requires the participation of proteins with an even higher level of organization. Such an organization is called quaternary structure. It is a functional association of several (two, three or more) protein molecules with a tertiary structural organization. An example of such a complex protein is hemoglobin. Its molecule consists of four interconnected molecules. Another example is the pancreatic hormone, insulin, which includes two components. In addition to protein subunits, the quaternary structure of some proteins also includes various non-protein components. The same hemoglobin contains a complex heterocyclic compound, which includes iron. Properties of the protein. Proteins, like other inorganic and organic compounds, have a number of physicochemical properties determined by their structural organization. This largely determines the functional activity of each molecule. First, proteins are primarily water-soluble molecules.

Secondly, protein molecules carry a large surface charge. This determines a number of electrochemical effects, for example, changes in membrane permeability, catalytic activity of enzymes and other functions.

Third, proteins are thermolabile, i.e. they exhibit their activity within a narrow temperature range.

The action of elevated temperature, as well as dehydration, changes in pH and other influences cause destruction of the structural organization of proteins. First, the weakest structure is destroyed - the quaternary, then the tertiary, secondary, and under more severe conditions - the primary. The loss of a protein molecule's structural organization is called denaturation.

If a change in environmental conditions does not lead to destruction of the primary structure of the molecule, then when normal environmental conditions are restored, the structure of the protein and its functional activity are completely recreated. This process is called renaturation. This property of proteins to completely restore the lost structure is widely used in the medical and food industries for the preparation of certain medical preparations, for example antibiotics, vaccines, serums, enzymes; to obtain food concentrates that retain their nutritional properties for a long time in dried form.

Functions of proteins. The functions of proteins in a cell are extremely diverse. One of the most important is the plastic (construction) function: proteins are involved in the formation of all cell membranes and cell organelles, as well as extracellular structures.

The catalytic role of proteins is extremely important. All biological catalysts - enzymes - are substances of protein nature; they accelerate chemical reactions occurring in the cell by tens and hundreds of thousands of times.

The interaction of an enzyme (F) with a substance (C), resulting in the formation of reaction products (P)

Let's take a closer look at this important function. The term “catalysis,” which is found no less often in biochemistry than in the chemical industry, where catalysts are widely used, literally means “unbinding,” “liberation.” The essence of the catalytic reaction, despite the huge variety of catalysts and types of reactions in which they take part, basically boils down to the fact that the starting substances form intermediate compounds with the catalyst. They are relatively quickly converted into the final reaction products, and the catalyst is restored to its original form. Enzymes are the same catalysts. All laws of catalysis apply to them. But enzymes are protein in nature, and this gives them special properties. What do enzymes have in common with catalysts known from inorganic chemistry, such as platinum, vanadium oxide and other inorganic reaction accelerators, and what makes them different? The same inorganic catalyst can be used in many different industries. Enzymes are active only at physiological values ​​of the acidity of the solution, i.e. at a concentration of hydrogen ions that is compatible with life and normal functioning of a cell, organ or system.

Regulatory function of proteins consists in their control of metabolic processes: insulin, pituitary hormones, etc.

Motor function living organisms are provided with special contractile proteins. These proteins are involved in all types of movement that cells and organisms are capable of: the flickering of cilia and the movement of flagella in protozoa, muscle contraction in multicellular animals, the movement of leaves in plants, etc.

Transport function of proteins consists of attaching chemical elements (for example, oxygen to hemoglobin) or biologically active substances (hormones) and transferring them to various tissues and organs of the body. Special transport proteins move RNA synthesized in the cell nucleus into the cytoplasm. Transport proteins are widely represented in the outer membranes of cells; they transport various substances from the environment into the cytoplasm.

When foreign proteins or microorganisms enter the body, special proteins are formed in white blood cells - leukocytes - called antibodies. They are connected

interact with substances (antigens) that are unusual for the body according to the principle of correspondence of the spatial configurations of molecules (the “key-lock” principle). As a result of this, a harmless, non-toxic complex is formed - “antigen-antibody”, which is subsequently phagocytosed and digested by other forms of leukocytes - this is a protective function.

Proteins can also serve as one of the sources of energy in the cell, that is, they perform an energy function. When 1 g of protein is completely broken down into final products, 17.6 kJ of energy is released. However, proteins are rarely used in this capacity. Amino acids released during the breakdown of protein molecules are involved in plastic exchange reactions to build new proteins.

Questions and tasks for review

What organic substances are included in the composition of the cell?

What simple organic compounds are proteins made of?

What are peptides?

What is the primary structure of a protein?

How are the secondary and tertiary structures of proteins formed?

What is protein denaturation?

What functions of proteins do you know?

Choose the correct answer option in your opinion.

1. Who discovered the existence of cells?

Robert Hooke

Carl Linnaeus

2. What is the cell filled with?

Cytoplasm

shell

3. What is the name of the dense body located in the cytoplasm?

core

shell

organoids

4. Which organelle helps the cell breathe?

lysosome

mitochondria

membrane

5. Which organelle gives green color to plants?

lysosome

chloroplast

mitochondria

6. What substance is most abundant in inorganic cells?

water

mineral salts

7. What substances make up 20% of an organic cell?

Nucleic acids

Squirrels

8. What common name can be used to combine the following substances: sugar, fiber, starch?

carbohydrates

9. Which substance provides 30% of the cell’s energy?

fats

carbohydrates

10. What substance is most abundant in the cell?

Oxygen

Amino acids, proteins. The structure of proteins. Levels of organization of a protein molecule

Video tutorialBybiology " Squirrels"

Functionsproteins

Resources

V. B. ZAKHAROV, S. G. MAMONTOV, N. I. SONIN, E. T. ZAKHAROVA TEXTBOOK “BIOLOGY” FOR GENERAL EDUCATIONAL INSTITUTIONS (grades 10-11).

A. P. Plekhov Biology with fundamentals of ecology. Series “Textbooks for universities. Special literature".

Book for teachers Sivoglazov V.I., Sukhova T.S. Kozlova T. A. Biology: general patterns.

Presentation hosting

11 .04.2012 Lesson 57 Grade 10

Lesson on: Proteins are natural polymers, composition and structure.

Lesson objectives: 1. To familiarize students with natural protein polymers.

2. Study their structure, classification and properties.

3. Consider the biological role and applications of proteins.

Equipment and reagents: from practical work No. 7.

During the classes:

Repetition of the covered topic.

We answer the questions asked on the screen:

What compounds are called amino acids?

What FGs are included in amino acids?

How are amino acid names constructed?

What types of isomerism are characteristic of amino acids?

What amino acids are called essential? Give examples.

What compounds are called amphoteric? Do amino acids have amphoteric properties? Justify your answer.

What chemical properties are characteristic of amino acids?

What reactions are called polycondensation reactions? Are polycondensation reactions typical for amino acids?

Which group of atoms is called the amide group?

What compounds are called polyamide? Give examples of polyamide fibers. What amino acids are suitable for producing synthetic fibers?

What compounds are called peptides?

Which group of atoms is called peptide?

Studying a new topic.

Determination of proteins.

Proteins are natural polymers with high molecular weights, the molecules of which are built from amino acid residues connected by peptide bonds.

The distribution of proteins in nature, their biological functions and significance for life on earth.

The structure of proteins.

a) primary structure - amino acid sequence, the number of amino acid units in a molecule can range from several tens to hundreds of thousands. This is reflected in the molecular weight of proteins, varying from 6500 (insulin) to 32 million (influenza virus protein);

b) secondary - in space, the polypeptide chain can be twisted into a spiral, on each turn of which there are 3.6 amino acid units with radicals facing outward. Individual turns are held together by hydrogen bonds between the ==N -H and ==C=O groups of different sections of the chain;

c) the tertiary structure of a protein is the ability to arrange a helix in space. The protein molecule is folded into a ball - a globule, which retains its spatial shape due to disulfide bridges –S -S. The figure shows the tertiary structure of the hexakinase enzyme molecule, which catalyzes the alcoholic fermentation of glucose. The depression in the globule is clearly visible, with the help of which the protein captures the glucose molecule and in which it undergoes further chemical transformations.

d) quaternary protein structure - some proteins (for example hemoglobin) are a combination of several protein molecules with non-protein fragments called prosthetic groups. Such proteins are called complex or peptides. The structure of a protein is the quaternary structure of a protein. The figure shows a schematic representation of the quaternary structure of the hemoglobin molecule. It is a combination of two pairs of polypeptide chains and four non-protein fragments, indicated by red disks. Each of them is a heme molecule. Those. complex complex of organic cycles with iron ion. Gemm has the same structure in all vertebrates and is responsible for the red color of blood.

5. Chemical properties of proteins

1) Denaturation

2) Hydrolysis

3) Qualitative reactions of proteins:

a) Biuret reaction

b) Xanthoprotein;

c) Qualitative determination of sulfur in proteins.

d) Combustion of proteins. When burning, squirrels emit a characteristic smell of burnt horn and hair. This smell is determined by the sulfur content in proteins (cysteine, methionine, cystine). If you add an alkali solution to a protein solution, heat it to a boil and add a few drops of lead acetate solution. A black precipitate of lead sulfide precipitates.

III. Homework P. 27? 1-10, Read 27. Ex. 1-10

"Life is a way of existence of protein bodies"

F. Engels.

None of the living organisms known to us can do without proteins. Proteins serve as nutrients, they regulate metabolism, acting as enzymes - metabolic catalysts, promote the transfer of oxygen throughout the body and its absorption, play an important role in the functioning of the nervous system, are the mechanical basis of muscle contraction, participate in the transfer of genetic information, etc. d.

Proteins (polypeptides) – biopolymers built from α-amino acid residues connected peptide(amide) bonds. These biopolymers contain 20 types of monomers. Such monomers are amino acids. Each protein is a polypeptide in its chemical structure. Some proteins consist of several polypeptide chains. Most proteins contain an average of 300-500 amino acid residues. There are several very short natural proteins, 3-8 amino acids long, and very long biopolymers, more than 1500 amino acids long. The formation of a protein macromolecule can be represented as a polycondensation reaction of α-amino acids:

Amino acids are connected to each other due to the formation of a new bond between carbon and nitrogen atoms - peptide (amide):

From two amino acids (AA) a dipeptide can be obtained, from three - a tripeptide, from a larger number of AAs polypeptides (proteins) are obtained.

Functions of proteins

The functions of proteins in nature are universal. Proteins are part of the brain, internal organs, bones, skin, hair, etc. Main sourceα - amino acids for a living organism are food proteins, which, as a result of enzymatic hydrolysis in the gastrointestinal tract, giveα - amino acids. Manyα - amino acids are synthesized in the body, and some are necessary for protein synthesis α - amino acids are not synthesized in the body and must come from outside. Such amino acids are called essential. These include valine, leucine, threonine, methionine, tryptophan, etc. (see table). In some human diseases, the list of essential amino acids expands.

· Catalytic function - carried out with the help of specific proteins - catalysts (enzymes). With their participation, the speed of various metabolic and energy reactions in the body increases.

Enzymes catalyze the reactions of breakdown of complex molecules (catabolism) and their synthesis (anabolism), as well as DNA replication and RNA template synthesis. Several thousand enzymes are known. Among them, such as pepsin, break down proteins during digestion.

· Transport function - binding and delivery (transport) of various substances from one organ to another.

Thus, hemoglobin, a protein in red blood cells, combines with oxygen in the lungs, turning into oxyhemoglobin. Reaching organs and tissues with the bloodstream, oxyhemoglobin breaks down and releases the oxygen necessary to ensure oxidative processes in tissues.

· Protective function - binding and neutralization of substances entering the body or resulting from the activity of bacteria and viruses.

The protective function is performed by specific proteins (antibodies - immunoglobulins) formed in the body (physical, chemical and immune defense). For example, the protective function is performed by the blood plasma protein fibrinogen, participating in blood clotting and thereby reducing blood loss.

· Contractile function (actin, myosin) – as a result of the interaction of proteins, movement in space, contraction and relaxation of the heart, and movement of other internal organs occur.

· Structural function - Proteins form the basis of the structure of the cell. Some of them (connective tissue collagen, hair, nails and skin keratin, vascular wall elastin, wool keratin, silk fibroin, etc.) perform almost exclusively a structural function.

In combination with lipids, proteins participate in the construction of cell membranes and intracellular formations.

· Hormonal (regulatory) function - the ability to transmit signals between tissues, cells or organisms.

Proteins act as metabolic regulators. They refer to hormones that are produced in the endocrine glands, some organs and tissues of the body.

· Nutritional function - carried out by reserve proteins, which are stored as a source of energy and substance.

For example: casein, egg albumin, egg proteins ensure the growth and development of the fetus, and milk proteins serve as a source of nutrition for the newborn.

The diverse functions of proteins are determined by the α-amino acid composition and structure of their highly organized macromolecules.

Physical properties of proteins

Proteins are very long molecules that consist of amino acid units linked by peptide bonds. These are natural polymers; the molecular weight of proteins ranges from several thousand to several tens of millions. For example, milk albumin has a molecular weight of 17,400, blood fibrinogen - 400,000, viral proteins - 50,000,000. Each peptide and protein has a strictly defined composition and sequence of amino acid residues in the chain, which determines their unique biological specificity. The number of proteins characterizes the degree of complexity of the organism (E. coli - 3000, and in the human body there are more than 5 million proteins).

The first protein that we become acquainted with in our lives is chicken egg protein albumin - it is highly soluble in water, when heated it coagulates (when we fry scrambled eggs), and when stored in a warm place for a long time it is destroyed and the egg goes rotten. But protein is hidden not only under the eggshell. Hair, nails, claws, fur, feathers, hooves, the outer layer of skin - they are all almost entirely composed of another protein, keratin. Keratin does not dissolve in water, does not coagulate, does not collapse in the ground: the horns of ancient animals are preserved in it just as well as bones. And the protein pepsin, contained in gastric juice, is capable of destroying other proteins, this is the process of digestion. The inferferon protein is used in the treatment of runny nose and flu, because kills the viruses that cause these diseases. And the protein from snake venom can kill a person.

Protein classification

From the point of view of the nutritional value of proteins, determined by their amino acid composition and the content of so-called essential amino acids, proteins are divided into full-fledged And inferior . Complete proteins include mainly proteins of animal origin, except for gelatin, which is classified as incomplete proteins. Incomplete proteins are mainly of plant origin. However, some plants (potatoes, legumes, etc.) contain complete proteins. Among animal proteins, proteins from meat, eggs, milk, etc. are especially valuable for the body.

In addition to peptide chains, many proteins also contain non-amino acid fragments; according to this criterion, proteins are divided into two large groups - simple and complex proteins (proteids). Simple proteins contain only amino acid chains; complex proteins also contain non-amino acid fragments ( For example, hemoglobin contains iron).

Based on their general type of structure, proteins can be divided into three groups:

1. Fibrillar proteins - insoluble in water, form polymers, their structure is usually highly regular and is maintained mainly by interactions between different chains. Proteins that have an elongated thread-like structure. The polypeptide chains of many fibrillar proteins are located parallel to each other along one axis and form long fibers (fibrils) or layers.

Most fibrillar proteins are not soluble in water. Fibrillar proteins include, for example, α-keratins (they account for almost the entire dry weight of hair, proteins of wool, horns, hooves, nails, scales, feathers), collagen - the protein of tendons and cartilage, fibroin - the protein of silk).

2. Globular proteins - water soluble, the general shape of the molecule is more or less spherical. Among globular and fibrillar proteins, subgroups are distinguished. Globular proteins include enzymes, immunoglobulins, some protein hormones (for example, insulin), as well as other proteins that perform transport, regulatory and auxiliary functions.

3. Membrane proteins - have domains that cross the cell membrane, but parts of them protrude from the membrane into the intercellular environment and the cytoplasm of the cell. Membrane proteins function as receptors, that is, they transmit signals and also provide transmembrane transport of various substances. Transporter proteins are specific; each of them allows only certain molecules or a certain type of signal to pass through the membrane.

Proteins are an integral part of animal and human food. A living organism differs from a nonliving one primarily by the presence of proteins. Living organisms are characterized by a huge variety of protein molecules and their high order, which determines the high organization of a living organism, as well as the ability to move, contract, reproduce, the ability to metabolize and perform many physiological processes.

Protein structure

Fischer Emil German, German organic chemist and biochemist. In 1899 he began work on protein chemistry. Using the ether method of analyzing amino acids, which he created in 1901, F. was the first to carry out qualitative and quantitative determinations of protein breakdown products, discovered valine, proline (1901) and hydroxyproline (1902), and experimentally proved that amino acid residues are linked to each other by peptide bonds; in 1907 he synthesized an 18-membered polypeptide. F. showed the similarity of synthetic polypeptides and peptides obtained as a result of protein hydrolysis. F. was also involved in the study of tannins. F. created a school of organic chemists. Foreign corresponding member of the St. Petersburg Academy of Sciences (1899). Nobel Prize (1902).

Goals:

Educational: form a holistic understanding of biopolymers –

proteins based on the integration of chemistry and biology courses. To introduce students to the composition, structure, properties and functions of proteins. Use experiments with proteins to implement interdisciplinary connections and to develop students’ cognitive interest.

Developmental: develop cognitive interest in subjects, the ability to reason logically, and apply knowledge in practice.

Educating: develop skills of joint activity, form the ability for self-esteem.

Lesson type: learning new knowledge.

DURING THE CLASSES

Organizing time.

Greetings, marking those absent. Voice the topic of the lesson and the purpose of the lesson.

Updating attention

Modern science represents the process of life as follows:

“Life is an interweaving of the most complex chemical processes of interaction between proteins and other substances.”

“Life is a way of existence of protein bodies”

F. Engels

Today we will look at proteins from a biological and chemical point of view.

Learning new material.

1. Concept of proteins

Protein is muscles, connective tissues (tendons, ligaments, cartilage). Protein molecules are included in the composition of bone tissue. Hair, nails, teeth, and skin are woven from special forms of protein. Separate very important hormones are formed from protein molecules, on which health depends. Most enzymes also include protein fragments, and the quality and intensity of physiological and biochemical processes occurring in the body depend on enzymes.

The protein content in different human tissues varies. Thus, muscles contain up to 80% protein, spleen, blood, lungs - 72%, skin - 63%, liver - 57%, brain - 15%, adipose tissue, bone and dental tissue - 14-28%.

Proteins are high-molecular natural polymers built from amino acid residues connected by an amide (peptide) bond -CO-NH-. Each protein is characterized by a specific amino acid sequence and individual spatial structure. Proteins account for at least 50% of the dry mass of organic compounds in an animal cell.

2. Composition and structure of proteins.

The composition of protein substances includes carbon, hydrogen, oxygen, nitrogen, sulfur, and phosphorus.

Hemoglobin – C 3032 H 4816 ABOUT 872 N 780 S 8 Fe 4 .

The molecular weight of proteins ranges from several thousand to several million. Mr egg protein = 36,000, Mr muscle protein = 1,500,000.

The study of protein hydrolysis products helped to establish the chemical composition of protein molecules and their structure.

In 1903, the German scientist Emil Hermann Fischer proposed the peptide theory, which became the key to the secret of protein structure. Fischer proposed that proteins are polymers of amino acid residues linked by an NH–CO peptide bond. The idea that proteins are polymer formations was expressed back in 1888 by Russian scientist Alexander Yakovlevich Danilevsky.

3. Definition and classification of proteins

Proteins are natural high-molecular natural compounds (biopolymers), built from alpha amino acids connected by a special peptide bond. Proteins contain 20 different amino acids, which means there is a huge variety of proteins with different combinations of amino acids. Just as we can form an infinite number of words from 33 letters of the alphabet, we can form an infinite number of proteins from 20 amino acids. There are up to 100,000 proteins in the human body.

The number of amino acid residues included in the molecules is different: insulin - 51, myoglobin - 140. Hence the M r of the protein is from 10,000 to several million.

Proteins are divided into proteins (simple proteins) and proteids (complex proteins).

4. Protein structure

A strictly defined sequence of amino acid residues in a polypeptide chain is called the primary structure. It is often called a linear chain. This structure is characteristic of a limited number of proteins.

Research has shown that some parts of the polypeptide chain are folded into a spiral due to hydrogen bonds between the – CO and – NH groups. This is how a secondary structure is formed.

The helical polypeptide chain must be somehow folded or compacted. When packed, protein molecules have an ellipsoidal shape, often called a coil. This is a tertiary structure formed by hydrophobic ones. Ester bonds, some proteins have S–S bonds (bisulfide bonds)

The highest organization of protein molecules is the quaternary structure - protein macromolecules connected to each other, forming a complex.

Functions of proteins

The functions of proteins in the body are varied. They are largely due to the complexity and diversity of the forms and composition of the proteins themselves.

Construction (plastic) – proteins are involved in the formation of the cell membrane, organelles and cell membranes. Blood vessels, tendons, and hair are built from proteins.

Catalytic – all cellular catalysts are proteins (active centers of the enzyme).

Motor – contractile proteins cause all movement.

Transport – The blood protein hemoglobin attaches oxygen and carries it to all tissues.

Protective – production of protein bodies and antibodies to neutralize foreign substances.

Energy – 1 g of protein is equivalent to 17.6 kJ.

Receptor – reaction to an external stimulus.

Knowledge generation:

Students answer the questions:

What are proteins?

How many spatial structures of a protein molecule do you know?

What functions do proteins perform?

Set and announce grades.

Homework : § 38 without chemical properties. Prepare a message on the topic “Is it possible to completely replace protein foods with carbohydrates?”, “The role of proteins in human life”