Proteins are biopolymers, the monomers of which are alpha-amino acid residues interconnected by peptide bonds. The amino acid sequence of each protein is strictly defined; in living organisms, it is encrypted by means of a genetic code, on the basis of which the biosynthesis of protein molecules takes place. 20 amino acids are involved in building proteins.

There are the following types of structure of protein molecules:

1. Primary. It is an amino acid sequence in a linear chain.
2. Secondary. This is a more compact stacking of polypeptide chains through the formation of hydrogen bonds between peptide groups. There are two variants of the secondary structure - alpha helix and beta folding.
3. Tertiary. Represents the laying of a polypeptide chain into a globule. In this case, hydrogen, disulfide bonds are formed, and the stabilization of the molecule is also realized due to hydrophobic and ionic interactions of amino acid residues.
4. Quaternary. A protein consists of several polypeptide chains that interact with each other through non-covalent bonds.

Thus, amino acids connected in a certain sequence form a polypeptide chain, the individual parts of which coil or form folds. Such elements of secondary structures form globules, forming the tertiary structure of the protein. Individual globules interact with each other, forming complex protein complexes with a quaternary structure.

Protein classification

There are several criteria by which protein compounds can be classified. The composition distinguishes between simple and complex proteins. Complex protein substances contain non-amino acid groups in their composition, the chemical nature of which may be different. Depending on this, there are:

• glycoproteins;
• lipoproteins;
• nucleoproteins;
• metalloproteins;
• phosphoproteins;
• chromoproteins.

There is also a classification according to the general type of structure:

• fibrillar;
• globular;
• membrane.

Proteins are called simple (one-component) proteins, consisting only of amino acid residues. Depending on the solubility, they are divided into the following groups:

Protein name	Solubility	Examples
Prolamins	Slightly soluble in water, well - in 70-80% ethanol. Contains large amounts of arginine.	Proteins are characteristic of cereal seeds (hordein is found in barley, zein in corn).
Histones	Soluble in weak hydrochloric acid.	They are present in the chromatin that makes up chromosomes.
Scleroproteins (protenoids)	Insoluble in water, saline liquids, dilute acids and alkalis.	Contained in supporting tissues (bones, hair, cartilage, tendons). They include a lot of proline, alanine, glycine.
Albumins	Soluble in water and salt solutions.	Lactoalbumin - milk protein, seroalbumin - blood serum.
Globulins	They dissolve well in low concentration salt solutions.	They are part of legumes and oil plants (phaseolin - bean seeds, legumin - pea seeds, etc.).
Protamines	Dissolve in acids.	They are found in considerable quantities in the germ cells of humans and animals. For example, in the sperm of fish (salmin - the salmon family).
Glutelins	Soluble in alkalis.	Contained in plants: fruits and green parts. Wheat grain gliadin, together with glutenin, forms gluten, due to which the dough becomes elastic. [ЗМ1]

Such a classification is not entirely accurate, because according to recent studies, many simple proteins are associated with a minimum number of non-protein compounds. So, some proteins contain pigments, carbohydrates, sometimes lipids, which makes them more like complex protein molecules.

Physico-chemical properties of protein

The physicochemical properties of proteins are determined by the composition and number of amino acid residues included in their molecules. The molecular weights of polypeptides vary greatly, from a few thousand to a million or more. The chemical properties of protein molecules are diverse, including amphotericity, solubility, and the ability to denature.

Amphoteric

Since proteins contain both acidic and basic amino acids, the molecule will always contain free acidic and free basic groups (COO- and NH3+, respectively). The charge is determined by the ratio of basic and acidic amino acid groups. For this reason, proteins are charged “+” if the pH decreases, and vice versa, “-” if the pH increases. In the case when the pH corresponds to the isoelectric point, the protein molecule will have zero charge. Amphotericity is important for the implementation of biological functions, one of which is maintaining the pH level in the blood.

Solubility

The classification of proteins according to the property of solubility has already been given above. The solubility of proteins in water is explained by two factors:

• charge and mutual repulsion of protein molecules;
• the formation of a hydration shell around the protein - water dipoles interact with charged groups on the outer part of the globule.

Denaturation

The physicochemical property of denaturation is the process of destruction of the secondary, tertiary structure of a protein molecule under the influence of a number of factors: temperature, the action of alcohols, salts of heavy metals, acids and other chemical agents.

Important! The primary structure is not destroyed during denaturation.

Chemical properties of proteins, qualitative reactions, reaction equations

The chemical properties of proteins can be considered using the reactions of their qualitative detection as an example. Qualitative reactions make it possible to determine the presence of a peptide group in a compound:

1. Xanthoprotein. When high concentrations of nitric acid act on the protein, a precipitate is formed, which, when heated, becomes yellow.

2. Biuret. Under the action of copper sulfate on a weakly alkaline protein solution, complex compounds are formed between copper ions and polypeptides, which is accompanied by staining the solution in a violet-blue color. The reaction is used in clinical practice to determine the concentration of protein in blood serum and other biological fluids.

Another important chemical property is the detection of sulfur in protein compounds. For this purpose, an alkaline protein solution is heated with lead salts. This gives a black precipitate containing lead sulfide.

The biological significance of protein

Due to their physical and chemical properties, proteins perform a large number of biological functions, which include:

• catalytic (enzyme proteins);
• transport (hemoglobin);
• structural (keratin, elastin);
• contractile (actin, myosin);
• protective (immunoglobulins);
• signal (receptor molecules);
• hormonal (insulin);
• energy.

Proteins are important for the human body, since they are involved in the formation of cells, provide muscle contraction in animals, and carry many chemical compounds together with blood serum. In addition, protein molecules are a source of essential amino acids and perform a protective function, participating in the production of antibodies and the formation of immunity.

Top 10 Little Known Protein Facts

1. Proteins began to be studied since 1728, it was then that the Italian Jacopo Bartolomeo Beccari isolated protein from flour.
2. Recombinant proteins are now widely used. They are synthesized by modifying the bacterial genome. In particular, insulin, growth factors and other protein compounds that are used in medicine are obtained in this way.
3. Protein molecules have been found in Antarctic fish that prevent blood from freezing.
4. The resilin protein is characterized by ideal elasticity and is the basis of the attachment points of insect wings.
5. The body has unique chaperone proteins that are able to restore the correct native tertiary or quaternary structure of other protein compounds.
6. In the nucleus of the cell there are histones - proteins that take part in the compaction of chromatin.
7. The molecular nature of antibodies - special protective proteins (immunoglobulins) - began to be actively studied since 1937. Tiselius and Kabat used electrophoresis and proved that in immunized animals the gamma fraction was increased, and after the absorption of serum by the provoking antigen, the distribution of proteins by fractions returned to the picture of the intact animal.
8. Egg white is a vivid example of the implementation of a reserve function by protein molecules.
9. In the collagen molecule, every third amino acid residue is formed by glycine.
10. In the composition of glycoproteins, 15-20% are carbohydrates, and in the composition of proteoglycans their share is 80-85%.

Conclusion

Proteins are the most complex compounds, without which it is difficult to imagine the vital activity of any organism. More than 5,000 protein molecules have been isolated, but each individual has its own set of proteins and this differs from other individuals of its species.

The most important chemical and physical properties of proteins updated: March 21, 2019 by: Scientific Articles.Ru

As you know, proteins are the basis for the origin of life on our planet. But it was the coacervate drop, consisting of peptide molecules, that became the basis for the birth of living things. This is beyond doubt, because an analysis of the internal composition of any representative of the biomass shows that these substances are found in everything: plants, animals, microorganisms, fungi, viruses. Moreover, they are very diverse and macromolecular in nature.

These structures have four names, all of them are synonyms:

• proteins;
• proteins;
• polypeptides;
• peptides.

protein molecules

Their number is truly incalculable. In this case, all protein molecules can be divided into two large groups:

• simple - consist only of amino acid sequences connected by peptide bonds;
• complex - the structure and structure of the protein are characterized by additional protolytic (prosthetic) groups, also called cofactors.

Moreover, complex molecules also have their own classification.

Gradation of complex peptides

1. Glycoproteins are closely related compounds of protein and carbohydrate. Prosthetic groups of mucopolysaccharides are woven into the structure of the molecule.
2. Lipoproteins are a complex compound of protein and lipid.
3. Metalloproteins - metal ions (iron, manganese, copper and others) act as a prosthetic group.
4. Nucleoproteins - the connection of protein and nucleic acids (DNA, RNA).
5. Phosphoproteins - the conformation of a protein and an orthophosphoric acid residue.
6. Chromoproteins are very similar to metalloproteins, however, the element that is part of the prosthetic group is a whole colored complex (red - hemoglobin, green - chlorophyll, and so on).

Each group considered has a different structure and properties of proteins. The functions they perform also vary depending on the type of molecule.

Chemical structure of proteins

From this point of view, proteins are a long, massive chain of amino acid residues interconnected by specific bonds called peptide bonds. From the side structures of the acids depart branches - radicals. This structure of the molecule was discovered by E. Fischer at the beginning of the 21st century.

Later, proteins, the structure and functions of proteins were studied in more detail. It became clear that there are only 20 amino acids that form the structure of the peptide, but they can be combined in a variety of ways. Hence the diversity of polypeptide structures. In addition, in the process of life and performance of their functions, proteins are able to undergo a number of chemical transformations. As a result, they change the structure, and a completely new type of connection appears.

To break the peptide bond, that is, to break the protein, the structure of the chains, you need to choose very harsh conditions (the action of high temperatures, acids or alkalis, a catalyst). This is due to the high strength in the molecule, namely in the peptide group.

The detection of the protein structure in the laboratory is carried out using the biuret reaction - exposure to the freshly precipitated polypeptide (II). The complex of the peptide group and the copper ion gives a bright violet color.

There are four main structural organizations, each of which has its own structural features of proteins.

Organization levels: primary structure

As mentioned above, a peptide is a sequence of amino acid residues with or without inclusions, coenzymes. So the primary name is such a structure of the molecule, which is natural, natural, is truly amino acids connected by peptide bonds, and nothing more. That is, a polypeptide of a linear structure. At the same time, the structural features of proteins of such a plan are that such a combination of acids is decisive for the performance of the functions of a protein molecule. Due to the presence of these features, it is possible not only to identify the peptide, but also to predict the properties and role of a completely new, not yet discovered. Examples of peptides with a natural primary structure are insulin, pepsin, chymotrypsin, and others.

Secondary conformation

The structure and properties of proteins in this category change somewhat. Such a structure can be formed initially from nature or when the primary structure is exposed to severe hydrolysis, temperature, or other conditions.

This conformation has three varieties:

1. Smooth, regular, stereoregular coils built from amino acid residues that twist around the main axis of the connection. They are held together only by those arising between the oxygen of one peptide group and the hydrogen of another. Moreover, the structure is considered correct due to the fact that the turns are evenly repeated every 4 links. Such a structure can be either left-handed or right-handed. But in most known proteins, the dextrorotatory isomer predominates. Such conformations are called alpha structures.
2. The composition and structure of proteins of the following type differs from the previous one in that hydrogen bonds are formed not between residues adjacent to one side of the molecule, but between significantly distant, and at a sufficiently large distance. For this reason, the entire structure takes the form of several wavy, serpentine polypeptide chains. There is one feature that a protein must exhibit. The structure of amino acids on the branches should be as short as possible, like glycine or alanine, for example. This type of secondary conformation is called beta sheets for the ability to seem to stick together when forming a common structure.
3. Biology refers to the third type of protein structure as complex, scattered, disordered fragments that do not have stereoregularity and are capable of changing the structure under the influence of external conditions.

No examples of proteins having a secondary structure by nature have been identified.

Tertiary education

This is a fairly complex conformation called a "globule". What is such a protein? Its structure is based on the secondary structure, however, new types of interactions between the atoms of the groups are added, and the whole molecule seems to curl up, thus focusing on the fact that the hydrophilic groups are directed inside the globule, and the hydrophobic ones are outward.

This explains the charge of the protein molecule in colloidal solutions of water. What types of interactions are present here?

1. Hydrogen bonds - remain unchanged between the same parts as in the secondary structure.
2. interactions - occur when the polypeptide is dissolved in water.
3. Ionic attraction - formed between differently charged groups of amino acid residues (radicals).
4. Covalent interactions - are able to form between specific acid sites - cysteine ​​molecules, or rather, their tails.

Thus, the composition and structure of proteins with a tertiary structure can be described as polypeptide chains folded into globules that retain and stabilize their conformation due to various types of chemical interactions. Examples of such peptides: phosphoglycerate kenase, tRNA, alpha-keratin, silk fibroin, and others.

Quaternary structure

This is one of the most complex globules that proteins form. The structure and functions of proteins of this kind are very versatile and specific.

What is such a conformation? These are several (in some cases dozens) large and small polypeptide chains that are formed independently of each other. But then, due to the same interactions that we considered for the tertiary structure, all these peptides twist and intertwine with each other. In this way, complex conformational globules are obtained, which can contain metal atoms, lipid groups, and carbohydrate groups. Examples of such proteins are DNA polymerase, tobacco virus envelope, hemoglobin, and others.

All the peptide structures we have considered have their own identification methods in the laboratory, based on modern possibilities of using chromatography, centrifugation, electron and optical microscopy, and high computer technologies.

Functions performed

The structure and function of proteins are closely correlated with each other. That is, each peptide plays a certain role, unique and specific. There are also those who are able to perform several significant operations in one living cell at once. However, it is possible to express in a generalized form the main functions of protein molecules in the organisms of living beings:

1. Ensuring movement. Unicellular organisms, or organelles, or some types of cells are capable of locomotion, contraction, movement. This is provided by proteins that are part of the structure of their motor apparatus: cilia, flagella, cytoplasmic membrane. If we talk about cells incapable of moving, then proteins can contribute to their contraction (muscle myosin).
2. Nutritional or reserve function. It is the accumulation of protein molecules in the eggs, embryos and seeds of plants to further replenish the missing nutrients. When cleaved, peptides give amino acids and biologically active substances that are necessary for the normal development of living organisms.
3. Energy function. In addition to carbohydrates, proteins can also give strength to the body. With the breakdown of 1 g of the peptide, 17.6 kJ of useful energy is released in the form of adenosine triphosphoric acid (ATP), which is spent on vital processes.
4. Signal and It consists in the implementation of careful monitoring of ongoing processes and the transmission of signals from cells to tissues, from them to organs, from the latter to systems, and so on. A typical example is insulin, which strictly fixes the amount of glucose in the blood.
5. receptor function. It is carried out by changing the conformation of the peptide on one side of the membrane and involving the other end in the restructuring. At the same time, the signal and the necessary information are transmitted. Most often, such proteins are built into the cytoplasmic membranes of cells and exercise strict control over all substances passing through it. They also alert you to chemical and physical changes in the environment.
6. Transport function of peptides. It is carried out by channel proteins and carrier proteins. Their role is obvious - transporting the necessary molecules to places with a low concentration from parts with a high one. A typical example is the transport of oxygen and carbon dioxide through organs and tissues by the protein hemoglobin. They also carry out the delivery of compounds with a low molecular weight through the cell membrane inside.
7. structural function. One of the most important of those that protein performs. The structure of all cells, their organelles is provided precisely by peptides. They, like a frame, set the shape and structure. In addition, they support it and modify it if necessary. Therefore, for growth and development, all living organisms need proteins in the diet. These peptides include elastin, tubulin, collagen, actin, keratin and others.
8. catalytic function. Enzymes do it. Numerous and varied, they accelerate all chemical and biochemical reactions in the body. Without their participation, an ordinary apple in the stomach could be digested in only two days, with a high probability of rotting. Under the action of catalase, peroxidase and other enzymes, this process takes two hours. In general, it is thanks to this role of proteins that anabolism and catabolism are carried out, that is, plastic and

Protective role

There are several types of threats that proteins are designed to protect the body from.

First, traumatic reagents, gases, molecules, substances of various spectrums of action. Peptides are able to enter into chemical interaction with them, converting them into a harmless form or simply neutralizing them.

Secondly, there is a physical threat from wounds - if the fibrinogen protein does not transform into fibrin in time at the site of injury, then the blood will not clot, which means that blockage will not occur. Then, on the contrary, you will need the plasmin peptide, which is capable of resolving the clot and restoring the patency of the vessel.

Thirdly, the threat to immunity. The structure and significance of proteins that form immune defenses are extremely important. Antibodies, immunoglobulins, interferons are all important and significant elements of the human lymphatic and immune system. Any foreign particle, harmful molecule, dead part of the cell or the whole structure is subjected to immediate investigation by the peptide compound. That is why a person can independently, without the help of medicines, daily protect himself from infections and simple viruses.

Physical Properties

The structure of a cell protein is very specific and depends on the function performed. But the physical properties of all peptides are similar and boil down to the following characteristics.

1. The weight of the molecule is up to 1,000,000 Daltons.
2. Colloidal systems are formed in an aqueous solution. There, the structure acquires a charge that can vary depending on the acidity of the medium.
3. When exposed to harsh conditions (irradiation, acid or alkali, temperature, and so on), they are able to move to other levels of conformations, that is, denature. This process is irreversible in 90% of cases. However, there is also a reverse shift - renaturation.

These are the main properties of the physical characteristics of peptides.

Protein molecules are made up of amino acid residues connected in a chain by peptide bonds.

Peptide bond occurs during the formation of proteins as a result of the interaction of the amino group ( -NH2) one amino acid with a carboxyl group ( -COOH) of another amino acid.

Two amino acids form a dipeptide (a chain of two amino acids) and a water molecule.

Dozens, hundreds and thousands of amino acid molecules combine with each other to form giant protein molecules.

Groups of atoms are repeated many times in protein molecules -CO-NH-; they are called amide, or in protein chemistry peptide groups. Accordingly, proteins are classified as natural high molecular weight polyamides or polypeptides.

The total number of naturally occurring amino acids reaches 300, but some of them are quite rare.

Among the amino acids, a group of the 20 most important is distinguished. They are found in all proteins and are called alpha amino acids.

The whole variety of proteins in most cases is formed by these twenty alpha-amino acids. At the same time, for each protein, the sequence in which the residues of its constituent amino acids are connected to each other is strictly specific. The amino acid composition of proteins is determined by the genetic code of the organism.

Proteins and peptides

And squirrels, and peptides are compounds built from amino acid residues. The differences between them are quantitative.

It is assumed that:

· peptides contain up to 100 amino acid residues in a molecule
(which corresponds to a molecular weight up to 10,000), and

· squirrels- over 100 amino acid residues
(molecular weight from 10,000 to several million).

In turn, in the group of peptides, it is customary to distinguish:

· oligopeptides(low molecular weight peptides),
containing in the chain no more 10 amino acid residues, and

· polypeptides, whose chain includes up to 100 amino acid residues.

For macromolecules with the number of amino acid residues approaching or slightly exceeding 100, the concepts of polypeptides and proteins are practically not distinguished and are often synonymous.

The structure of proteins. Organization levels.

A protein molecule is an extremely complex entity. The properties of a protein depend not only on the chemical composition of its molecules, but also on other factors. For example, from the spatial structure of the molecule, from the bonds between the atoms that make up the molecule.

Allocate four levels structural organization of the protein molecule.

Primary Structure

The primary structure is the arrangement of amino acid residues in polypeptide chains.

The sequence of amino acid residues in a chain is the most important characteristic of a protein. It is she who determines its main properties.

Each person's protein has its own unique primary structure associated with the genetic code.

secondary structure.

The secondary structure is related to the spatial orientation of the polypeptide chains.

Its main types:

the alpha helix

betta structure (looks like a folded sheet).

The secondary structure is fixed, as a rule, by hydrogen bonds between the hydrogen and oxygen atoms of the peptide groups, which are 4 units apart from each other.

Hydrogen bonds, as it were, sew the helix together, holding the polypeptide chain in a twisted state.

Tertiary structure

Wherever we meet life
we find that she is bound
with any protein body.

F.Engels

Goals. Expand knowledge about proteins as natural polymers, about the variety of their functions in relation to their structure and properties; use experiments with proteins to implement interdisciplinary connections and to develop students' interest.

Study Plan

• The role of proteins in the body.
• Composition, structure, properties of proteins.
• Protein functions.
• Synthesis of proteins.
• Transformation of proteins in the body.

DURING THE CLASSES

The role of proteins in the body

Biology teacher. Of the organic substances that make up a living cell, proteins play the most important role. They account for about 50% of the cell mass. Thanks to proteins, the body acquired the ability to move, multiply, grow, assimilate food, respond to external influences, etc.
“Life is a mode of existence of protein bodies, the essential moment of which is the constant exchange of substances with the external nature surrounding them, and with the cessation of this exchange of substances, life also stops, which leads to the decomposition of the protein,” Engels wrote in his writings.

Composition, structure, properties of proteins

Chemistry teacher. Proteins are complex high-molecular natural compounds built from α-amino acids. The composition of proteins includes 20 different amino acids, hence the huge variety of proteins with various combinations of amino acids. Just as we can make an infinite number of words from 33 letters of the alphabet, so from 20 amino acids we can make an infinite number of proteins. There are up to 100,000 proteins in the human body.
Proteins are divided into proteins (simple proteins) and proteins (complex proteins).
The number of amino acid residues included in the molecules is different: insulin - 51, myoglobin - 140. Hence M r protein from 10,000 to several million.
History reference . The first hypothesis about the structure of the protein molecule was proposed in the 70s of the XIX century. This was the ureide theory of protein structure. In 1903, the German scientist E. G. Fischer proposed the peptide theory, which became the key to the mystery of the structure of the protein. Fisher suggested that proteins are polymers of amino acid residues connected by NH-CO peptide bonds. The idea that proteins are polymeric formations was expressed as early as 1888 by the Russian scientist A.Ya. Danilevsky. This theory was confirmed in subsequent works. According to the polypeptide theory, proteins have a definite structure.
(Demonstration of the film fragment "Primary, secondary, tertiary protein structure.")
Many proteins are composed of several polypeptide particles that fold into a single aggregate. So, the hemoglobin molecule (C 738 H 1166 S 2 Fe 4 O 208) consists of four subunits. Note that M r egg protein = 36,000, M r muscle protein = 1,500,000.

Primary structure of a protein – the sequence of alternation of amino acid residues (all bonds are covalent, strong) (Fig. 1).

secondary structure - the shape of the polypeptide chain in space. The protein chain is twisted into a spiral (due to many hydrogen bonds) (Fig. 2).

Tertiary structure is the real three-dimensional configuration that a twisted helix assumes in space (due to hydrophobic bonds); in some proteins, S–S bonds (bisulfide bonds) (Fig. 3).

Quaternary structure – protein macromolecules connected to each other form a complex (Fig. 4).

Chemical properties of proteins

When proteins and peptides are heated with solutions of acids, alkalis, or under the action of enzymes, hydrolysis occurs. Hydrolysis of proteins is reduced to the cleavage of polypeptide bonds:

Laboratory experience 1.
Protein denaturation

Denaturation - violation of the natural structure of the protein under the influence of heating and chemical reagents.
a) The effect of alcohol on protein;
b) the effect of sodium chloride salts (concentrated solution) and lead acetate on protein;
c) the action of HNO 3 (conc.);
d) coagulation of proteins during boiling.

Laboratory experience 2.
Color qualitative reactions of proteins

a) Biuret reaction;
b) xantoprotein reaction;
c) interaction of protein with lead acetate during heating.

Chemistry teacher. The data of experiment 1 show that pollution of the natural environment with salts of heavy metals leads to negative consequences for living organisms. Natural proteins lose their specific properties, become insoluble, and denature. When poisoning people with salts of heavy metals, milk is used, the proteins of which bind ions of such metals.
(Demonstration of a fragment from the 1st part of the film "Proteins, the structure of protein molecules.")

Functions of proteins

Biology teacher. The functions of proteins are varied.

1. Building material - proteins are involved in the formation of the cell membrane, organelles and cell membranes. Blood vessels, tendons, and hair are built from proteins.
2. Catalytic role - all cellular catalysts are proteins (active sites of the enzyme). The structure of the active site of the enzyme and the structure of the substrate exactly match each other, like a key and a lock.
3. Motor function - contractile proteins cause any movement.
4. Transport function The blood protein hemoglobin attaches oxygen and carries it to all tissues.
5. Protective role - production of protein bodies and antibodies to neutralize foreign substances.
6. Energy function – 1 g of protein is equivalent to 17.6 kJ.

Protein synthesis

Biology teacher. Humans have been consuming proteins isolated mainly from plants and animals for a long time. In recent decades, work has been carried out on the artificial production of protein substances. Half of the globe is in a state of protein starvation, and the global shortage of dietary protein is about 15 million tons per year at a protein intake rate per day for an adult of 115 g.
(Demonstration of a fragment of the 2nd part of the film "Proteins, the structure of protein molecules" - about the assembly of a protein molecule.)

Transformation of proteins in the body

Chemistry teacher. Findings. All proteins are polypeptides, but not all polypeptides are proteins. Each protein has its own specific structure.

Homework .Rudzitis G.E., Feldman F.G.. Chemistry-11. M.: Enlightenment, 1992, p. 18–22.

LITERATURE

Makarenya A.A. Let's go back to chemistry. Moscow: Higher school, 1989;
Chemistry manual. Organic chemistry for training in educational institutions of medical and biological profile. Rostov-on-Don: Publishing House of Rostov University, 1995;
Koltun M. The world of chemistry. M.: Children's literature, 1988;
Reading book on organic chemistry. Comp. P.F. Butskus. Moscow: Education, 1985;
Chertkov I.N. Polymer experiment in high school. M.: Education, 1971;
Body T.V., Kalyakina E.A. Squirrels. "Chemistry" (Publishing house "First of September"), 2003, No. 3,
with. fourteen;
Belyaev D.K., Vorontsov N.N., Dymyshts G.M. and etc. General biology. Moscow: Enlightenment, 1999, 287 p.

Squirrels- high-molecular organic compounds consisting of amino acid residues connected in a long chain by a peptide bond.

The composition of the proteins of living organisms includes only 20 types of amino acids, all of which are alpha-amino acids, and the amino acid composition of proteins and their order of connection with each other are determined by the individual genetic code of a living organism.

One of the features of proteins is their ability to spontaneously form spatial structures characteristic only for this particular protein.

Due to the specificity of their structure, proteins can have a variety of properties. For example, proteins having a globular quaternary structure, in particular chicken egg protein, dissolve in water to form colloidal solutions. Proteins with a fibrillar quaternary structure do not dissolve in water. Fibrillar proteins, in particular, form nails, hair, cartilage.

Chemical properties of proteins

Hydrolysis

All proteins are capable of undergoing hydrolysis. In the case of complete hydrolysis of proteins, a mixture of α-amino acids is formed:

Protein + nH 2 O => mixture of α-amino acids

Denaturation

The destruction of the secondary, tertiary and quaternary structures of a protein without destroying its primary structure is called denaturation. Protein denaturation can proceed under the action of solutions of sodium, potassium or ammonium salts - such denaturation is reversible:

Denaturation occurring under the influence of radiation (for example, heating) or processing of the protein with salts of heavy metals is irreversible:

So, for example, irreversible protein denaturation is observed during the heat treatment of eggs during their preparation. As a result of egg white denaturation, its ability to dissolve in water with the formation of a colloidal solution disappears.

Qualitative reactions to proteins

Biuret reaction

If a 10% sodium hydroxide solution is added to a solution containing protein, and then a small amount of a 1% copper sulfate solution, a violet color will appear.

protein solution + NaOH (10% solution) + СuSO 4 = violet color

xantoprotein reaction

protein solutions when boiled with concentrated nitric acid turn yellow:

protein solution + HNO 3 (conc.) => yellow color

Biological functions of proteins

catalytic	speed up various chemical reactions in living organisms	enzymes
structural	cell building material	collagen, cell membrane proteins
protective	protect the body from infections	immunoglobulins, interferon
regulatory	regulate metabolic processes	hormones
transport	transfer of vital substances from one part of the body to another	hemoglobin carries oxygen
energy	supply the body with energy	1 gram of protein can provide the body with 17.6 J of energy
motor (motor)	any motor function of the body	myosin (muscle protein)