The main amino acids are only 20. Their names are associated with random moments. All amino acids that are part of natural proteins are α-amino acids. This means that the amino and carboxyl group are located in a single carbon atom.

1. Aminoacetic acid (glycine);

2. α-aminopropian acid (alanine);

3. α- Aminocentanic acid (valine);

4. α-aminoisocapronic acid (leucine);

5. α-amino-β-methylvaleryanic acid (isoleucine);

6. α-amino-β-hydroxypropane acid (serine);

7. α-amino-β-hydroxyma salted acid (threonine);

Sulfur-containing:

8. α-amino-β-mercaptopropanic acid (cysteine);

9. α-amino-γ-methylthiomaslaic acid (methionine);

10. α-aminoantic acid (asparagic acid);

11. asparagic acid amide (asparagin);

12. α-aminohlutaric acid (glutamic acid);

13. amide α-aminoglutaric acid (gutamine);

14. α, ε-diaminocapronic acid (leases);

15. α-amino-δ-guanidylovalerian acid

(arginine);

Cyclic :

16. α-amino-β-phenylpropane acid (phenylalanine);

17. α-amino-β-para-hydroxyphenylproavy acid (tyrosine);

18. α-amino-β-imidozolilpropane xylotol (histsion);

19. α-amino-β-indolylpropane xylota (tryptophan);

20. α-tetrahydropyrolcarboxylic acid (proline).

All natural amino acids belong to the L-stereochemical series, D-row only as an exception for bacteria, as part of a capsules to protect the bacteria from enzymes.

Lecture 3..

For each amino acid, their only physico-chemical properties are characterized - isoelectric point, i.e. The pH of the medium in which the solution of this amino acid is electronically. (Q \u003d 0).

If we consider such acid in the aqueous medium, then dissociation occurs on the acidic and the main type - bipolar ion.

In the organism of mammalian in the liver there is an enzyme oxidase-D-amino acid, which selectively destroys D-amino acids that fall into food. D-amino acids found as part of some peptides of microorganisms. In addition, D-amino acids are part of a large number of antibiotics. For example, D-valine, D-leucine is part of the antibiotic grainidine, D-phenylalanine is part of the grainidine-C, penicillin contains an unusual fragment of D-dimethylcysteine.



The process of racification (transition D in L) is not enzymatically, so very slowly. This is found to determine the age of mammals.

All amino acids have an amino and carboxyl group in their composition possess the properties of amines and carboxylic acids. In addition, for α-amino acids is characteristic ningidrin reaction (Common with proteins). With alcohol ninhydrine, a blue-violet color appears very quickly, with a yellow propine.

At the end of the XIX century there was a controversy, how the amino acids form a connection if you take two amino acids, merge them together, it will never be a linear structure (due to thermodynamics, cyclization occurs). Get the polypeptide in the XIX century did not work in any way.

Linear molecules will not work. With tz.Termodynamics more profitably press 2N 2 O than to form a linear molecule.

In 1888, Danilevsky's chemist suggested that proteins are polypeptides, linear molecules that are formed as a result of the action of a carboxyl group of one amino acid with a carboxyl group of another amino acid cleavage and a dipptide is formed:

An amide bond is formed (for peptide proteins), these peptide bonds are separated by only one carbon atom. Based biuret reaction Danilevsky made such a conclusion. This reaction of a protein solution with copper sulfate in an alkaline medium is formed, a cine-purple staining is formed, a mining complex with copper ions is formed, as a result of the fact that the peptide bond in protein molecules has a specific structure. Due to the keto-enol tautomeria, it is half a double, half single. Characteristic reaction with CU (OH) 2:

The buret reaction is characteristic of Biuret (Fig. 1), for Malonamide (Fig. 2), proteins.

In order to finally prove that it was blenced - this polypeptides in 1901 Fisher synthesized the polypeptide, regardless of him, Hoffman also synthesized the polypeptide:

Synthesis of polypeptide on Fisher:

The product gave a buret reaction, poorly dissolved, did not possess biological activity, split off with protolytic enzymes, and enzymes are specific biocatalysts that split natural proteins, which means that this product has the same structure as natural proteins.

Currently, more than 2 thousand different proteins are synthesized. The main thing in the synthesis of protein is the protection of the amino group and the activation of the carboxyl group so that the synthesis is directed. The protection of amino groups is carried out by acylation, for this is treated with trichloroacetic acid anhydrides and trifluoricular groups are introduced, or treated according to zelers (chloro-acid benzyl ester).

For the synthesis of each particular polypeptide, its own methods can be carried out to stitch a particular site.

Protection in Survy, activation by Kurcius, removal of protection for Beckman :

The solid phase synthesis of polypeptides and proteins, a specific feature of the polypeptide synthesis is a huge number of similar operations. The method was developed Robert Merifilodem . The monomers are amino acids that are used for synthesis containing a protected amino group and activated carboxyl groups - synthons. Merifield suggested: the first monomer is fixed on a polymer resin (insoluble carrier) and all subsequent operations are carried out with a polymer-based polypeptide, another synthon and reagent are added to the resin to remove the terminal protecting group. Chemical stages are mixed with appropriate flushing. During the entire process, the polypeptide remains associated with the resin. This process can be easily automated, programming the change of streams through the column. Currently, devices are developed synthesizers. At the final stage of the synthesis, the covalent polypeptide is associated with the resin, removed from this resin and the protective group is removed. One of the most important problems in solid-phase synthesis is the ratification of amino acids during the synthesis. This is especially dangerous in this synthesis, because The intermediate stages of the separation of racimates do not exist. The methods of separation at the moment do not exist, but there are conditions so that as little as possible is racmization. Merofield himself received several polypeptides at once, bradykidine was obtained - a hormone with a vasodilatory action, angiotensin - a hormone, boiling blood pressure, a ribonuclease enzyme that catalyzes RNA hydrolysis.

The output of the products this method is not consistent with the methods that have been used before. Using automation, you can use this method on an industrial scale.

Each polypeptide has a n-end, and the other with the end. Amino acid, which takes part changes the ending on the IL

Glycil-Valil-Tyirosyl-histsion-Asparagil Proline. To determine the amino acids in the polypeptide, it is necessary to conduct hydrolysis, it is carried out at 100 ° C for 24 hours 6N hydrochloric acid. Next, hydrolysis products are analyzed - separated by the method of ion exchange chromatography on a sulfalized polystyrene column. Then wash the citrate buffer from the column. By the number of eluent, they judge what acids, i.e. At the beginning, acidic acids will be washed, and the most recent are basic. Thus, it can be determined at what point which amino acid has passed, and the amount is determined by the photometrically with the help of Ningdrin, this method can determine 1 μg. If it is necessary to open 1 ng, a fluoroscanine is used, it reacts with α-amino acids, forming a highly fluorosculating compound. They determine which and how many amino acids are, and the sequence of amino acids cannot be determined.

Fluoroselanine:

1. What substances are biological polymers? What substances are monomers to build biopolymer molecules?

Biological polymers are: b) nucleic acids; c) polysaccharides; e) proteins.

Monomers for constructing biopolymer molecules are: a) amino acids; d) nucleotides; e) monosaccharides.

2. What functional groups are characteristic of all amino acids? What properties do these groups have?

For all amino acids, the presence of an amino group (-NH 2), which has basic properties, and carboxyl group (-son) with acid properties.

3. How many amino acids involved in the formation of natural proteins? Name the general features of the structure of these amino acids. What do they differ?

20 amino acids participate in the formation of natural proteins. Such amino acids are called protein-forming. In their molecules, the carboxyl group and the amino group are associated with the same carbon atom. On this basis, protein-forming amino acids are similar to each other.

Belone-forming amino acids differ in the composition and structure of the lateral group (radical). It can be non-polar or polar (neutral, sour, main), hydrophobic or hydrophilic, which gives each amino acid special properties.

4. How are the amino acids connect to the polypeptide chain? Build a dipeptide and tripipedeptide. To perform the task, use the structural formulas of the amino acids shown in Figure 6.

Amino group (-NH 2) of one amino acid is capable of interacting with a carboxyl group (-son) of another amino acid. This distinguishes the water molecule, and a peptide connection arises between the amino nitrogen atom and the carbon atom. The resulting molecule is a dipeptide, at one end of the molecule of which there is a free amino group, and on the other - a free carboxyl group. Thanks to this, the dipeptide can attach other amino acids, forming oligopeptides. If more than 10 residues of amino acids are connected in this way, the polypeptide is formed.

The structural formula of the dipeptide (for example, ala-deep) can be represented as follows:

The structural formula of the Tripeptide (for example, the de-ala-liz) can be represented as follows:

5. Describe the levels of the structural organization of proteins. What chemical ties determine different levels of the structural organization of protein molecules?

Protein molecules can take various spatial forms that are four levels of their structural organization.

The chain (linear sequence) of amino acid residues connected by peptide bonds is the primary structure of the protein molecule. Each organism protein has a unique primary structure. Other types of structures are created based on the primary structure, so it is the primary structure that determines the form, properties and function of protein.

The secondary structure arises as a result of the formation of hydrogen bonds between atoms of hydrogen NH groups and oxygen atoms of CO groups of different amino acid residues of the polypeptide chain.

The tertiary structure is formed by the formation of hydrogen, ionic, disulfide (S-S bonds between the residues of cysteine \u200b\u200bamino acids) and other bonds arising between different groups of the protein molecule atoms in the aqueous medium. In this case, the polypeptide spiral is stacked in a peculiar ball (globe) in such a way that hydrophobic amino acid radicals are immersed in the globule, and hydrophilic are located on the surface and interact with water molecules.

The composition of molecules of some proteins is not one, but several polypeptides forming a single complex. This is how a quaternary structure is formed. Polypeptides are not associated with covalent bonds, the strength of the quaternary structure is ensured by the interaction of weak intermolecular forces.

Thus, the primary structure of the protein molecule is due to the presence of peptide bonds between the residues of amino acids. The secondary structure will stabilize hydrogen bonds, tertiary - hydrogen, ionic, disulfide, etc., quaternary - weak intermolecular interactions.

6. Man and animals get amino acids from food. What can amino acids in plants can be synthesized?

Plants - autotrophic organisms. They synthesize amino acids from the primary photosynthesis products (which, in turn, are formed from carbon dioxide and water) and nitrogen-containing inorganic compounds (ammonium ions, nitrate ions). Thus, in plants, the initial substances for the synthesis of amino acids are CO 2, H 2 O, NH 4 + (NH 3), NO 3 -.

7. How many different tripeptides can be constructed from three amino acid molecules (for example, alanine, lysine and glutamic acid), if each amino acid can only be used once? Will these peptides have the same properties?

You can build six tripipeptides: ala-liz-deep, ala-depth Liz, Liz-Ala-Gland, Liz-Glu-ala, Glou-Al Liz and the Glu-Liza Ala. All the resulting peptides will have different properties.

8. To separate the mixture of proteins on the components, the electrophoresis method is used: in the electric field, separate protein molecules are moved to one of the electrodes in a certain speed. At the same time, some proteins move towards the cathode, others move to the anode. How is the structure of a protein molecule associated with its ability to move in an electric field? What depends on the direction of movement of protein molecules? What does their speed depend on?

In aqueous solutions, the radicals of acid amino acids included in the protein are charged negative due to the dissociation of carboxyl groups:

-Oson → -coo - + H +

The radicals of the main amino acids have a positive charge due to the attachment of hydrogen ions (H +) to nitrogen atoms, which are part of these radicals:

-NH 2 + H + → NH 3 +

The carboxyl group and the amino group, which are at the ends of the polypeptide chain, also acquire a charge (negative and positive, respectively). Thus, in a solution, the protein molecule has a certain total charge, which causes its movement in the electric field.

The charge of the protein molecule depends on the ratio of the residues of acidic and basic amino acids. If the residues of acid amino acids prevail in the composition of the protein, then the total charge of the molecule will be negative and it will move to the anode (positively charged electrode). If the residues of the main amino acids prevail, the total charge of the molecule will be positive, and the protein will move towards the cathode (negatively charged electrode).

Motion speed depends primarily on the charge of the protein molecule, its mass and spatial configuration.

Chapter III. Proteins

§ 6. Amino acids as structural elements of proteins

Natural amino acids

Amino acids in living organisms are found primarily as part of proteins. Proteins are built mostly twenty standard amino acids. They are A-amino acids and differ from each other by the structure of lateral groups (radicals), denoted by the letter R:

A variety of lateral amino acid radicals plays a key role in the formation of the spatial structure of proteins, when the active center of enzymes is functioning.

The structure of standard amino acids is given at the end of the paragraph in Table 3. Natural amino acids have trivial names, which are uncomfortable in records of the structure of proteins. Therefore, three-letter and one-borenitations are introduced for them, which are also presented in Table 3.

Spatial isomeria

In all amino acids, with the exception of glycine, a carbon atom is chiral, i.e. They are characterized by optical isomeria. In tab. 3 The chiral carbon atom is marked with an asterisk. For example, for Alanine, the projection of Fisher of both isomers look like this:

For their designation, as for carbohydrates, D, L-nomenclature is used. The protein includes only L-amino acids.

L- and D-isomers can mutually turn into each other. This process is called racemication.

Interesting to know! In protein teeth - dentine -L.-Sparagica Acid spontaneously racing at the temperature of the human body with a speed of 0.10% per year. During the formation of teeth in dentina only containsL.-Asparagic acid, in an adult person as a result of racemia is formedD.-Sparagic acid. The older man, the higher the content of the D-isomer. Deciding the ratio of D- and L-isomers, you can definitely establish age. Thus were exposed by residents of the mountain villages of Ecuador, which attributed to themselves too much age.

Chemical properties

Amino acids contain amino and carboxyl groups. By virtue of this, they show amphoteric properties, that is, properties and acids and bases.

When the amino acid is dissolved in water, for example, glycine, its carboxyl group dissociates with the formation of hydrogen ion. Next, the hydrogen ion is joined by the vapor pair of electrons at the nitrogen atom to the amino group. Ion is formed, in which positive and negative charges are present at the same time, the so-called zwitter ion:

This form of amino acid is predominant in neutral solution. In the acidic medium of the amino acid, connecting the hydrogen ion, forms the cation:

Anion is formed in the alkaline environment:

Thus, depending on the pH of the amino acid medium, it can be a positively charged, negatively charged and electronic (with equality of positive and negative charges). The pH value of the solution at which the total charge of the amino acid is zero, is called isoelectric point This amino acid. For many amino acids, the isoelectric point lies near PH 6. For example, the isoelectric glycine and alanine points are 5.97 and 6.02, respectively.

Two amino acids can react with each other, as a result of which the water molecule is cleaved and the product is formed, which is called dipeptide:

Communication connecting two amino acids is called peptide bond. If you use the iconic symbols of amino acids, the formation of a dipeptide can be schematically represented as follows:

Similarly formed tripeptides, tetrapeptides etc.:

H 2 N - Liz - Ala - Gly - Soam - Tripeptide

H 2 N - TRP - GIS - Ala - Ala - Soon - Tetrapeptide

H 2 N - Tir - Liz - Gly - Ala - Lei - Gly - TRP - Soam - Heptapeptide

Peptides consisting of a small number of amino acid residues have a common name oligopeptides..

Interesting to know! Many oligopeptides have high biological activity. These include a number of hormones, for example, oxytocin (nanopepide) stimulates the cutting of the uterus, bradykinin (nanopepide) suppresses inflammatory processes in the tissues. The antibiotic gramicidine C (cyclic decapeptide) disrupts the regulation of ion permeability in the membranes of bacteria and thereby kills them. Amanitine mushroom poisons (octapeptides), blocking protein synthesis, can cause strong poisoning in humans. Aspartame is widely known - aspartilphenylalanine methyl ether. Aspartame has a sweet taste and is used to give a sweet taste with various products, drinks.

Classification of amino acids

There are several approaches to the classification of amino acids, but the most preferred classification based on the structure of their radicals is. Four grades of amino acids containing the radicals of the following types are distinguished; one) non-polar (or hydrophobic); 2) polar uncharged; 3) negatively charged and 4) positively charged:


Non-polar (hydrophobic) includes amino acids with non-polar aliphatic (alanine, valine, leucine, isoleucine) or aromatic (phenylalanine and tryptophan) R-groups and one session-containing amino acid - methionine.

Polar uncharged amino acids in comparison with non-polar is better dissolved in water, more hydrophilic, since their functional groups form hydrogen bonds with water molecules. These include amino acids containing a polar but-group (serine, threonine and tyrosine), HS group (cysteine), an amide group (glutamine, asparaginine) and glycine (R-group of glycine represented by one hydrogen atom, too small to compensate Strong polarity of A-amino group and A-carboxyl group).

Asparagic and glutamic acids relate to negatively charged amino acids. They contain two carboxyl and one amino group, therefore, in the ionized state, their molecules will have a total negative charge:

A positively charged amino acids belong to lysine, histidine and arginine, in ionized form they have a total positive charge:

Depending on the nature of the radicals, natural amino acids are also divided into neutral, sourand Maintenance. Neutral include non-polar and polar uncharged, to sour - negatively charged, to the main - positively charged.

Ten of 20 amino acids that are part of proteins can be synthesized in the human body. The rest should be contained in our food. These include Arginine, Valin, Isolecin, Leucin, Lizin, Methionine, Treonin, Triptofan, Phenylalanin and Gistidin. These amino acids are called indispensable. An indispensable amino acids are often included in the composition of food additives, used as drugs.

Interesting to know! An exceptionally important role is played by the balance of human nutrition in amino acids. With a lack of essential amino acids in food, the body is self-disseminated. In this case, it suffers primarily a brain, which leads to various diseases of the central nervous system, mental disorders. A young growing organism is especially vulnerable. For example, in violation of tyrosine synthesis from phenylalanine in children, severe disease is developing, phylinpyrograde oligophrenia, causing severe mental backwardness or death of a child.

Table 3.

Standard amino acids

Amino acid

(trivial name)

Legend

Structural formula

Latin

three-letter

oNNIBUK-VENENT

Non-polar (hydrophobic)

Isoleucine

Phenylalanine

Tryptophan

Metionine

Polar uncharged

Asparagin

Glutamine

The structure of amino acids

Amino acids- heterofunctional compounds that necessarily contain two functional groups: amino group -NH 2 and carboxyl group -Con-associated hydrocarbon radical.

The general formula of the simplest amino acids can be written as follows:

Since amino acids contain two different functional groups that affect each other, characteristic reactions differ from the characteristic reactions of carboxylic acids and amines.

Amino acid properties

Amino group -NH 2 determines the main properties of amino acids, since it is capable of attaching a hydrogen cation for a donor-acceptor mechanism due to the presence of a free electronic pair at the nitrogen atom.

Group -Oson (carboxyl group) determines the acidic properties of these compounds. Next, amino acids - it amphoteric organic compounds.

With alkalis, they react as acids:

With strong acids as base-amines:

In addition, the amino group in amino acid enters into interaction with the carboxyl group included in its composition, forming an internal salt:

Ionization of amino acid molecules depends on the acid or alkaline nature of the environment:

Since the amino acids in aqueous solutions behave like typical amphoteric compounds, then in living organisms they play the role of buffer substances supporting a certain concentration of hydrogen ions.

Amino acids are colorless crystalline substances that melted with decomposition at temperatures above 200 ° C. They are soluble in water and insoluble on the air. Depending on the R-radical, they can be sweet, bitter or tasteless.

Amino acids divided by natural (found in living organisms) and synthetic. Among natural amino acids (about 150), proteinogenic amino acids (about 20) are distinguished, which are part of proteins. They are l-forms. Approximately half of these amino acids belong to indispensable, so on. They are not synthesized in the human body. Indispensable are acids such as valine, leucine, isoleucine, phenylalanine, lysine, threonine, cysteine, methionine, histidine, tryptophan. In the human body, these substances come with food. If their quantity in food is insufficient, the normal development and functioning of the human body is violated. In case of individual diseases, the organism is not able to synthesize some other amino acids. So, with phenylketonuria, tyrosine is not synthesized.

The most important property of amino acids is the ability enter into molecular condensation with water release and the formation of amide grouping -NH-CO-, eg:

High molecular weight compounds obtained as a result of such a reaction contain a large number of amide fragments and therefore got a name polyamides.

In addition to the above-mentioned synthetic fiber of Capron, for example, and annta formed during polycondensation of aminoeantic acid is believed. To obtain synthetic fibers, amino acids are suitable with the arrangement of amino and carboxyl groups at the ends of the molecules.

Polyamides α-amino acids are called peptides. Depending on the number of residues, amino acids distinguish dipeptides, tripipeptides, polypeptides. In such compounds, the group -NH-COO call peptide.

Isomerius and amino acid nomenclature

Isomeria amino acidsdetermined by various structures of the carbon chain and the position of the amino group, for example:

The names of amino acids are widespread, in which the position of the amino group is indicated letters of the Greek Alphabet: α, β, γ, etc. Thus, 2-aminobutanic acid can also be called α-amino acid:

In the biosynthesis of protein in living organisms 20 amino acids are involved.

Proteins

Proteins- These are high molecular weight (molecular weight varies from 5-10 thousand to 1 million or more) Natural polymers, whose molecules are built from amino acid residues connected by amide (peptide) bond.

Proteins are also called proteins(Greek. "Protos" is the first, important). The number of amino acid residues in the protein molecule is very fluctuated and sometimes reaches several thousand. Each protein has its own sequence of amino acid residues.

Proteins are performed a variety of biological functions: Catalytic (enzymes), regulatory (hormones), structural (collagen, fibroin), motor (MIOSIN), transport (hemoglobin, mioglobin), protective (immunoglobulins, interferon), spare (casein, albumin, glyadin) and others.

Proteins performing certain specific functions depends on the spatial configuration of their molecules, in addition, the cell is energetically unprofitable to keep proteins in the unfolded form, in the form of a chain, so the polypeptide chains are subjected to laying, acquiring a certain three-dimensional structure, or conformation. Allocate 4 levels of spatial organization of proteins.

Proteins - the base of the biomembrane, the most important component of the cell and cellular components. They play a key role in cell life, making up the material basis for its chemical activities.

Exceptional protein property - self-organizing structure, i.e. its ability to spontaneously create a specific spatial structure inherent in this protein. Essentially, all the activities of the body (development, movement, the performance of various functions and much more) is associated with protein substances. Without proteins it is impossible to imagine life.

Proteins - the most important component of the food of man and animals, supplier of necessary amino acids.

The structure of proteins

In the spatial structure of proteins is of great importance radical(residues) R-in amino acid molecules. Non-polar radicals Amino acids are usually located inside the protein macromolecules and determine hydrophobic interactions; polar radicalscontaining ionic (forming ions) groups are usually located on the surface of the protein macromolecule and characterize electrostatic (ionic) interactions. Polar non-ionic radicals (For example, containing alcohol on-groups, amide groups) can be located both on the surface and inside the protein molecule. They are involved in education hydrogen ties.

In the molecules of protein of A-amino acids, peptide (-s-nh-) connections are related to each other:

Thus constructed polypeptide chains or individual sections inside the polypeptide chain may in some cases be additionally related to disulfide (-S-S-) connections or, as they are often called, disulfide bridges.

A big role in creating the structure of proteins is played ionic(salt) and hydrogen bonds, as well as hydrophobic interaction- A special type of contact between the hydrophobic components of protein molecules in the aquatic environment. All these bonds have different strength and ensure the formation of a complex, large protein molecule.

Despite the difference in the structure and functions of protein substances, their elemental composition varies slightly (in% on dry mass): carbon - 51-53; oxygen - 21.5-23.5; Nitrogen - 16.8-18.4; hydrogen - 6.5-7.3; sulfur - 0.3-2.5.

Some proteins contain phosphorus, selenium and other elements in small quantities. The sequence of compounding the amino acid residues in the polypeptide chain was called the primary protein structure. The protein molecule may consist of one or more of the polypeptide chains, each of which contains a different number of amino acid residues. Given the number of their possible combinations, it can be said that the diversity of proteins is almost limitless, but not all of them exist in nature. The total number of different types of proteins in all types of living organisms is 10 11 -10 12. For proteins, the structure of which is characterized by an exceptional complexity, except primary, distinguish between higher levels of structural organization: secondary, tertiary, and sometimes quaternary structures.

Secondary structureit has most of the proteins, however, not always all over the polypeptide chain. Polypeptide chains with a specific secondary structure can be located differently in space.

In formation tertiary structureIn addition to hydrogen bonds, ionic and hydrophobic interactions play a major role. By the nature of the "packaging" protein molecule distinguish globular, or spherical, and fibrillary, or filamentous, proteins.

For globular proteins, the α-spiral structure is more characteristic, the spirals are curved, "rolled". Macromolecule has a spherical shape. They dissolve in water and salt solutions with the formation of colloidal systems. Most animal proteins, plants and microorganisms belong to globular proteins.


- The sequence of arino acid residues in the polypeptide chain constituting the protein molecule. Communication between amino acids - peptide.

If the protein molecule consists of only 10 amino acid residues, then the number of theoretically possible variants of protein molecules, which differ in the alternation of amino acids - 1020. Having 20 amino acids, you can make an even more diverse combinations. There were about ten thousand different proteins in the human body, which differ from both each other and from proteins of other organisms.

Exactly primary structure The protein molecule determines the properties of protein molecules and its spatial configuration. Replacing just one amino acid to another in the polypeptide chain leads to a change in the properties and functions of the protein. For example, the replacement in the β-subunit of the hemoglobin of the sixth glutamic amino acid on the valine leads to the fact that the hemoglobin molecule as a whole cannot perform its main function - the oxygen transport; In such cases, a person develops a disease - sickle-cell anemia.

Secondary structure - Ordered coagulation of the polypeptide chain into a spiral (has a stretched spring). Spiral coils are strengthened with hydrogen bonds arising between carboxyl groups and amino groups. Almost all of the co- and nn groups take part in the formation of hydrogen bonds. They are weaker than peptide, but, repeating many times, give this configuration stability and rigidity. At the level of the secondary structure, there are proteins: fibroin (silk, web), keratin (hair, nails), collagen (tendon).

Tertiary structure - laying of polypeptide chains in globule arising from the occurrence of chemical bonds (hydrogen, ionic, disulfide) and establishing hydrophobic interactions between the radicals of amino acid residues. The main role in the formation of the tertiary structure is played by hydrophilic-hydrophobic interactions.

In aqueous solutions, hydrophobic radicals strive to hide from water, grouped inside the globule, while hydrophilic radicals as a result of hydration (interactions with water dipoles) tend to be on the surface of the molecule. In some proteins, the tertiary structure is stabilized by disulfide covalent bonds arising between the sulfur atoms of two cysteine \u200b\u200bresidues. At the level of the tertiary structure, there are enzymes, antibodies, some hormones.

Quaternary structure Characteristic for complex proteins, whose molecules are formed by two and more globule. Subunits are held in a molecule due to ionic, hydrophobic and electrostatic interactions. Sometimes during the formation of a quaternary structure between subunits, disulfide bonds arise. The most studied protein having a quaternary structure is hemoglobin. It is formed by two α-subunits (141 amino acid residues) and two β-subunits (146 amino acid residues). With each subunit, a hem molecule containing iron is connected.

If for any reason, the spatial conformation of proteins deviates from normal, the protein cannot perform its functions. For example, the cause of "cow's rabies" (gip-shaped encephalopathy) is an abnormal conformation of the prions - surface proteins of nerve cells.

For fibrillar proteins, a filamental structure is more characteristic. They, as a rule, do not dissolve in water. Fibrillar proteins typically perform structure-forming functions. Their properties (strength, ability to stretch) depend on the method of packaging polypeptide chains. An example of fibrillar proteins serve myosin, keratin. In some cases, individual protein subunits with hydrogen bonds, electrostatic and other interactions form complex ensembles. In this case, forms quaternary structure of proteins.

An example of a protein with a quaternary structure is hemoglobin of blood. Only with such a structure, it performs its functions - binding oxygen and transporting it into tissues and organs. However, it should be noted that in the organization of higher protein structures, an exceptional role belongs to the primary structure.

Classification of proteins

There are several classifications of proteins:

According to the degree of complexity (simple and complex).

In the form of molecules (globular and fibrillar proteins).

By solubility in individual solvents (water-soluble, soluble in dilute saline solutions - albumin, alcoholoisseable - prolamines, soluble in diluted alkalis and acids - vulnery).

According to the functions performed (for example, spare proteins, skeletal, etc.).

Properties of proteins

Proteins - amphoteric electrolytes. With a certain meaning of the medium (it is called an isoelectric point), the number of positive and negative charges in the protein molecule is equally. This is one of the main properties of the protein. Proteins at this point are either either, and their solubility in water is the smallest. The ability of proteins to reduce the solubility when the electronutrality is reached, their molecules is used to release from solutions, for example, in the technology of obtaining protein products.

Hydration. The hydration process means binding to water proteins, and they exhibit hydrophilic properties: swelling, their mass and volume increase. The swelling of individual proteins depends exclusively on their structure. Available and located on the surface of the protein macromolecule hydrophilic amide (-s-NH-, peptide bonds), amine (-NH 2) and carboxyl (-son) groups attract the water molecules, strictly orienting them on the surface of the molecule. The surrounding protein globules hydrate (aqueous) sheath prevents aggregation and precipitation, and therefore contributes to the stability of protein solutions. In the isoelectric point, proteins have the smallest ability to bind water, the destruction of the hydrate envelope occurs around protein molecules, so they are connected, forming large units. The aggregation of protein molecules occurs when they are dehydrated using some organic solvents, such as ethyl alcohol. This leads to the fallout of proteins in the sediment. With a change in the pH of the medium, the protein macromolecule becomes charged, and its hydration ability changes.

With limited swelling, concentrated protein solutions form complex systems, called jenby. The student is not fluid, elags, possess plasticity defined by mechanical strength, are able to maintain their shape. Globular proteins can be completely hydrated, dissolved in water (for example, milk proteins), forming solutions with low concentration. Hydrophilic properties of proteins, i.e. their ability to swell, form jelly, stabilize suspensions, emulsions and foam, are of great importance in biology and food industry. Very mobile jelly, built mainly of protein molecules, is a cytoplasm - raw gluten isolated from wheat dough; It contains up to 65% water.

Various hydrophilicitygluten proteins are one of the signs characterizing the quality of wheat grain and flour from it (so-called strong and weak wheat). The hydrophilicity of grain and flour proteins plays a major role when storing and processing grain, in bread maker. The dough that is obtained in bakery production is a swollen protein in water, a concentrated jelly containing starch grains.

Denaturation of proteins. When denaturated under the influence of external factors (temperature, mechanical effects, the action of chemical agents and a number of other factors), there is a change in the secondary, tertiary and quaternary structures of the protein macromolecule, that is, its native spatial structure. Primary structure, and therefore, the chemical composition of the protein does not change. Physical properties change: the solubility is reduced, the ability to hydration is lost, biological activity is lost. The form of a protein macromolecule is changing, aggregation occurs. At the same time, the activity of some chemical groups increases, the effects on proteolytic enzyme proteins are facilitated, and therefore it is easier hydrolyzed.

In the food technology, special practical importance is thermal denaturation of proteins, The degree of which depends on the temperature, the duration of heating and humidity. It must be remembered when developing heat treatment regimens of food raw materials, semi-finished products, and sometimes ready-made products. The processes of thermal denaturation play a special role when blanching vegetable raw materials, grain drying, bread pastries, macaroni production. Denaturation of proteins can be called and mechanically exposed (pressure, rubbing, shaking, ultrasound). Finally, the protein denaturation gives the effect of chemical reagents (acids, alkalis, alcohol, acetone). All these techniques are widely used in food and biotechnology.

Foaming. Under the process of foaming, the ability of proteins to form highly concentrated liquid-gas systems, called foams, is understood. The stability of the foam in which the protein is a foaming agent depends not only on its nature and on the concentration, but also on temperature. Proteins as foaming agents are widely used in the confectionery industry (grazing, marshmallow, souffle). The structure of the foam has bread, and this affects its taste.

Protein molecules under the influence of a number of factors can collapseor enter into interaction with other substances With the formation of new products. For the food industry, two important processes can be distinguished:

1) hydrolysis of proteins under the action of enzymes;

2) the interaction of amino groups of proteins or amino acids with carbonyl groups of restoring sugars.

Under the influence of protease enzymes catalyzing the hydrolytic cleavage of proteins, the latter disintegrate into simpler products (poly and dipeptides) and ultimately on amino acids. The speed of the hydrolysis of the protein depends on its composition, molecular structure, enzyme activity and conditions.

Hydrolysis of proteins. The reaction of hydrolysis with the formation of amino acids in general can be written as follows:

Combustion. Proteins are burning with nitrogen, carbon dioxide and water, as well as some other substances. The burning is accompanied by a characteristic smell of burnt feathers.

Colored reactions. For high-quality definition of protein use the following reactions:

1. Denaturation- The process of violation of the natural protein structure (the destruction of the secondary, tertiary, quaternary structure).

2. Hydrolysis- destruction of the primary structure in an acidic or alkali solution to form amino acids.

3. Qualitative protein reactions:

· buret;

Biuret reaction - Purple staining under the action of copper (II) salts in an alkaline solution. Such a reaction is given all compounds containing a peptide bond, in which the interaction of weakly alkaline solutions of proteins with a solution of copper sulfate (II) with the formation of complex compounds between Cu 2+ ions and polypeptides. The reaction is accompanied by the appearance of violet blue color.

· xanthoprotein;

Xanthoprotein reaction - The appearance of yellow staining under the action of concentrated nitric acid on proteins containing the residues of aromatic amino acids (phenylalanine, tyrosine), in which the interaction of aromatic and heteroatomic cycles in the protein molecule with concentrated nitric acid, accompanied by the appearance of yellow painting, occurs.

· the reaction of sulfur definition in proteins.

Cysteine \u200b\u200breaction (For proteins containing sulfur) - boiling protein solution with lead acetate (II) with the advent of black staining.

Reference material for testing:

Mendeleev table

Solubility table

Proteins and peptides.

Proteins - Natural high molecular weight nitrogen-containing organic compounds. They play a primary role in all life processes, are carriers of life. Proteins It is contained in all tissues of organisms, in the blood, in the bones.


Protein, as well as carbohydrates and fats, is the most important component of the human meal.

Chemical structure of proteins

Protein molecules consist of residual amino acids connected to a chain of peptide bond.



Peptide communication It occurs in the formation of proteins as a result of the interaction of the amino group ( -NH2) one amino acid with a carboxyl group ( -Oson) Other amino acids.


Of the two amino acids, a dipeptide is formed (a chain of two amino acids) and a water molecule.


Tens, hundreds and thousands of amino acid molecules, connecting with each other, form giant protein molecules.


In protein molecules, groups of atoms repeated many times -S-NH-; they are called amide, or in protein chemistry peptide groups. Accordingly, proteins refer to natural high molecular weight polyamides or polypeptides.


The total number of amino acids occurring in nature reaches 300, but some of them are rare enough.


Among the amino acids there is a group of 20 most important. They are found in all proteins and got a name alfa-amino acids.


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

Proteins and peptides

AND proteins, I. peptides. - These are compounds built from amino acid residues. Differences between them are peculiar.


Conventionally believe that:

  • peptides. contain in a molecule up to 100 amino acid residues
    (which corresponds to the molecular weight to 10,000), and
  • proteins - Over 100 amino acid residues
    (molecular weight from 10,000 to several million).

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

  • oligopeptides. (low molecular weight peptides),
    Containing in the chain no more 10 amino acid residues, and
  • polypeptides., whose circuit is included 100 amino acid residues.

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

Structure of proteins. Organization levels.


Protein molecule is an extremely complex education. Properties of protein depend not only on the chemical composition of its molecules, but also from other factors. For example, from the spatial structure of the molecule, on the bonds between atoms included in the molecule.


Highlight four levels structural organization of protein molecule.


1. Primary structure


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


The sequence of amino acid residues in the chain is the most important protein characteristic. It is it that determines its basic properties.


The protein of each person has its own unique primary structure associated with genetic code.


2. Secondary structure.


The secondary structure is associated with the spatial orientation of the polypeptide chains..


Its main types:

  • alpha Spiral,
  • betta structure (has a form of a folded sheet).

The secondary structure is enshrined, as a rule, hydrogen bonds between hydrogen atoms and oxygen of peptide groups, which are 4lled from each other.


Hydrogen bonds seek a spiral, holding the polypeptide chain in the twisted state.



3. Tertiary structure


The tertiary structure reflects the spatial form of the secondary structure.


For example, a secondary structure in the form of a helix, in turn, can have a spheroid or ovoid shape.


The tertiary structure is stabilized not only by hydrogen bonds, but also by other types of interaction, such as ionic, hydrophobic, as well as disulfide bonds.


4. Quaternary Structure


The first three levels are characteristic of the structural organization of all protein molecules.


The fourth level is found in the formation of protein complexes consisting of several polypeptide chains.


This is a complex supramolecular formation consisting of several proteins having their own primary, secondary and tertiary structures.


The protein with a quaternary structure can be included both identical and differing polypeptide chains.


The association of polypeptide chains into a quaternary structure can lead to the emergence of new biological properties that are absent in the initial proteins forming this structure.


In the stabilization of the quaternary structure, the same types of interactions are involved as in the stabilization of tertiary.

Classification of proteins

Due to the diversity of peptides and proteins there are several approaches to their classification. They can be classified according to biological functions, composition, spatial structure.


In composition, proteins are divided into:

  • Simple
  • Sophisticated.

Simple squirrels.


In the hydrolysis of simple proteins, only alpha-amino acids are obtained as the splitting products.


Sophisticated proteins.


Sophisticated proteins Along with the proper protein part, consisting of alpha-amino acids, contains the organic or inorganic parts of the non-peptide nature, called prosttic groups.


Examples of complex proteins can serve transport proteins mioglobin and hemoglobinin which the protein part is globin - connected to the prosthetic group - gEMOM. According to the type of promptic group they are referred to hemoproteins.


Phosphoprotein contain the residue of phosphoric acid, metaloproteins - Metal ions.


Mixed biopolymers are also complex proteins. Depending on the nature of the prosthetic group, they are divided into:

  • Glycoproteins (contain carbohydrate part)
  • Lipoproteins (contain lipid part),
  • Nucleoproteins(contain nucleic acids).

In the body, proteins are rarely found in "pure" form. Basically, they are part of complex formations with a high level of organization, including other biopolymers and various organic and inorganic groups as subunits.


In the spatial structure, proteins are divided into two large classes:

  • Globular I.
  • Fibrillar.

Globular proteins.


For globular proteins, the alpha spiral structure is more characteristic, and their chains are curved in space so that the macromolecule acquires the form of the sphere.


Globular proteins They dissolve in water and salt solutions with the formation of colloidal systems.


Examples of globular proteins - albumen (egg protein), globin (Bemoglobin protein), mioglobinAlmost all enzymes.


Fibrillar proteins.


For fibrillar proteins more characteristic betta Structure. As a rule, they have a fibrous structure, do not dissolve in water and salt solutions.


These include many widespread proteins - betta Ceratin (hair, horny cloth), betta Fibroin (silk), mioinozin (muscular fabric), collagen (connective tissue).

Functions of proteins in the body.

The classification of proteins according to their functions is quite conditional, since the same protein can perform several functions.


Below will list the basic functions of proteins in the body:


1. Catalytic function.


Proteins of this group are called enzymes. Enzymes catalyze various chemical reactions. For example, the reaction of cleavage of complex molecules (catabolism) and their synthesis (anabolism).


Examples of catalytic proteins: catalase, Alcoholdhydehydrogenase, Pepsin, Trypsin, Amilaza etc.


2. Structural function


Attach the shape of the cell and its organoids. For example, monomers aktin and tubulin Form long threads, of which the cytoskeleton consists, allowing the cell to support the form. Collagen and elastin - the main components of the intercellular substance of the connective tissue (for example, cartilage), and from another structural protein keratin Consist hair, nails, bird feathers and some shells.


3. Protective function


There are several types of protein protective functions:

  • Physical protection
    Physical protection of the body provide collagen - protein forms the basis
    Intercellular substance of connective tissues (including bones, cartilage,
    tendons and deep layers of skin (dermis)); keratinconstituting the basis of horny
    Shields, hair, feathers, horns, etc. derivatives of the epidermis. Usually such proteins
    Consider as proteins with a structural function. Examples of proteins of this group
    Serve fibrinogen and thrombinaParticipated in blood collapse.

  • Chemical protection
    The binding of toxins by protein molecules can ensure their detoxification.
    A particularly important role in the detoxification in humans play enzymes of the liver,
    splitting poisons or translating them in a soluble form, which contributes to them
    Fast removal from the body.

  • Immune defense
    Proteins included in the blood and other biological fluids involved in
    Protective response of the organism both on damage and on the attack of pathogens. They are
    Neutralize bacteria, viruses or alien proteins.

4. Regulatory function


Proteins of this group regulate various processes occurring in cells or in the body. The proteins of this group include: proteins-hormones, proteins receptors etc.


Hormones are transferred to blood. Most animal hormones are proteins or peptides. Hormones regulate the concentrations of substances in the blood and cells, growth, reproduction and other processes. An example of such proteins is insulin, which regulates blood glucose concentration.


5. Signal function


Signal function proteins - The ability of proteins to serve as signals, transmitting signals between cells, tissues, organs and organisms. Often, the signal function is combined with the regulatory, since many intracellular regulatory proteins also transmit signals.


The signal function is performed proteins-hormones, cytokines, growth factors et al. Hormone binding with its receptor is a signal that runs the cell response.


Cells interact with each other using signaling proteins transmitted through the intercellular substance. Such proteins include, for example, cytokines and growth factors.


6. Transport function


The participation of proteins in the transfer of substances into cells and from cells, in their displacements inside the cells, as well as in their transport with blood and other body fluids.


An example of transport proteins can be called hemoglobinwhich carries oxygen from the lungs to the rest of the tissues and carbon dioxide from the fabrics to the light, as well as the homologous proteins found in all the kingdoms of living organisms.


Some membrane proteins participate in the transport of small molecules through the cell membrane, changing its permeability.

7. Spare (backup) function


Such proteins include so-called backup proteins that are poisoned as a source of energy and substances in plant seeds (for example, 7S Globulins and 11S.) and animal eggs. A number of other proteins are used in the body as a source of amino acids. Examples of reserve proteins are casein, egg albumin.


8. Receptor function


Protein receptors can be located both in the cytoplasm and integrated into the cell membrane.


The receptors respond to a change in its spatial configuration to attach the molecule of a certain chemical transmitting an external regulatory signal and, in turn, transmits this signal into the cell or cell organelles.


9. Motor (Motor) Function


Motor protein, motor protein - class of molecular motors capable of moving. They transform the chemical energy contained in ATF, in the mechanical energy of movement.


Motor proteins provide the movements of the body, for example, cutting muscles.


Motor proteins include cytoskeleton proteins - dineyins, kinesins, as well as proteins involved in muscle contractions - aktin, mozin.