What are amino acids and what are their beneficial properties? Amino acids in bodybuilding Amino acid.

Among the variety of amino acids, only 20 are involved in intracellular protein synthesis ( proteinogenic amino acids). Also, about 40 more non-proteinogenic amino acids have been found in the human body. All proteinogenic amino acids are α- amino acids and their example can be shown additional ways classifications.

According to the structure of the side radical

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• aliphatic(alanine, valine, leucine, isoleucine, proline, glycine),
• aromatic(phenylalanine, tyrosine, tryptophan),
• sulfur-containing(cysteine, methionine),
• containing OH group(serine, threonine, tyrosine again),
• containing additional COOH group(aspartic and glutamic acids),
• additional NH 2 group(lysine, arginine, histidine, also glutamine, asparagine).

Usually the names of amino acids are abbreviated to a 3-letter designation. Molecular biology professionals also use single-letter symbols for each amino acid.

Structure of proteinogenic amino acids

According to the polarity of the side radical

Exist non-polar amino acids (aromatic, aliphatic) and polar(uncharged, negatively and positively charged).

According to acid-base properties

According to their acid-base properties they are divided into neutral(majority), sour(aspartic and glutamic acids) and basic(lysine, arginine, histidine) amino acids.

By irreplaceability

According to the need for the body, those that are not synthesized in the body and must be supplied with food are isolated - irreplaceable amino acids (leucine, isoleucine, valine, phenylalanine, tryptophan, threonine, lysine, methionine). TO replaceable include those amino acids whose carbon skeleton is formed in metabolic reactions and is capable of somehow obtaining an amino group to form the corresponding amino acid. The two amino acids are conditionally irreplaceable (arginine, histidine), i.e. their synthesis occurs in insufficient quantities, especially for children.

STRUCTURE AND PROPERTIES OF AMINO ACIDS INCLUDED IN PROTEINS. PEPTIDE BONDS CONNECTING AMINO ACIDS IN CHAINS

Proteins are polymer molecules in which amino acids serve as monomers. Only 20 α-amino acids are found in proteins in the human body. The same amino acids are present in proteins with different structures and functions. The individuality of protein molecules is determined by the order of alternation of amino acids in the protein. Amino acids can be considered as letters of the alphabet, with the help of which, as in a word, information is written. A word carries information, for example, about an object or action, and the sequence of amino acids in a protein carries information about the construction of the spatial structure and function of this protein.

A. Structure and properties of amino acids

1. General structural features of amino acids that make up proteins

A common structural feature of amino acids is the presence of amino and carboxyl groups connected to the same α-carbon atom. R - amino acid radical - in the simplest case it is represented by a hydrogen atom (glycine), but can have a more complex structure.

IN aqueous solutions at neutral pHα-amino acids exist as bipolar ions.

IN unlike 19 othersα-amino acids, proline is an imino acid, the radical of which is bonded to both the α-carbon atom and the amino group, as a result of which the molecule acquires a cyclic structure.

19 out of 20 amino acids contain an asymmetric carbon atom in the α-position, to which 4 different substituent groups are associated. As a result, these amino acids in nature can be found in two different isomeric forms - L and D. The exception is glycine, which does not have an asymmetric α-carbon atom, since its radical is represented only by a hydrogen atom. Proteins contain only L-isomers of amino acids.

Pure L- or D-stereoisomers can, over a long period of time, spontaneously and non-enzymatically transform into an equimolar mixture of L- and D-isomers. This process is called racemization. Racemization of each L-amino acid at a given temperature occurs at a certain rate. This circumstance can be used to determine the age of people and animals. Thus, hard tooth enamel contains the protein dentin, in which L-aspartate transforms into the D-isomer at human body temperature at a rate of 0.01% per year. During the period of tooth formation, dentin contains only the L-isomer, so the age of the subject can be calculated from the D-aspartate content.

All 20 amino acids in the human body differ in structure, size and physicochemical properties of the radicals attached to the α-carbon atom.

2. Classification of amino acids according to the chemical structure of radicals

According to their chemical structure, amino acids can be divided into aliphatic, aromatic and heterocyclic (Table 1-1).

Aliphatic radicals may contain functional groups that give them specific properties: carboxyl (-COOH), amino (-NH2), thiol

(-SH), amide (-CO-NH2), hydroxyl (-OH) and guanidine groups.

The names of amino acids can be constructed using substitutive nomenclature, but trivial names are usually used (Table 1-2).

Table 1-1. Classification of the main amino acids of proteins according to their chemical structure

Table 1-2. Examples of amino acid names according to substitution nomenclature and corresponding trivial names

To write amino acid residues in peptide and protein molecules, three-letter abbreviations of their trivial names are used, and in some cases, one-letter symbols (see Table 1-1).

Trivial names often come from the name of the source from which they were first isolated, or from the properties of a given amino acid. Thus, serie was first isolated from silk fibroin (from the Latin serieum - silky), and glycine got its name because of its sweet taste (from the Greek glykos - sweet).

3. Classification of amino acids according to the solubility of their radicals in water

All 20 amino acids in the proteins of the human body can be grouped according to the ability of their radicals to dissolve in water. The radicals can be arranged in a continuous series, starting with completely hydrophobic ones and ending with strongly hydrophilic ones.

The solubility of amino acid radicals is determined by the polarity of the functional groups that make up the molecule (polar groups attract water, non-polar groups repel it).

Amino acids with non-polar radicals

Non-polar (hydrophobic) radicals include radicals having aliphatic hydrocarbon chains (alanine, valine, leucine, isoleucine, proline and methionine radicals) and aromatic rings (phenylalanine and tryptophan radicals). The radicals of such amino acids in water tend to each other or to other hydrophobic molecules, as a result of which the surface of their contact with water decreases.

Amino acids with polar uncharged radicals

The radicals of these amino acids are better soluble in water than hydrophobic radicals, since they contain polar functional groups that form hydrogen bonds with water. These include series, threonine and tyrosine, which have

hydroxyl groups, asparagine and glutamine containing amide groups, and cysteine ​​with its thiol group.

Cysteine ​​and tyrosine contain thiol and hydroxyl groups, respectively, capable of dissociation to form H+, but at a pH of about 7.0, maintained in cells, these groups practically do not dissociate.

Amino acids with polar negatively charged radicals

This group includes aspartic and glutamic amino acids, which have an additional carboxyl group in the radical, which dissociates at a pH of about 7.0 to form COO- and H+. Therefore, the radicals of these amino acids are anions. The ionized forms of glutamic and aspartic acids are called glutamate and aspartate, respectively.

Amino acids with polar positively charged radicals

Lysine and arginine have an additional positively charged group in the radical. In lysine, the second amino group, capable of attaching H+, is located in the?- position of the aliphatic chain, and in arginine, the huanidine group acquires a positive charge. In addition, histidine contains a weakly ionized imidazole group, therefore, with physiological fluctuations in pH values ​​(from 6.9 to 7.4) histidine is charged either neutrally or positively. With an increase in the number of protons in the medium, the imidazole group of histidine is able to attach a proton, acquiring a positive charge, and with an increase in the concentration of hydroxyl groups, it can donate a proton, losing the positive charge of the radical. Positively charged radicals are cations (see diagram below).

Polar charged radicals of amino acids have the greatest solubility in water.

4. Change in the total charge of amino acids depending on the pH of the environment

At neutral pH values, all acidic (capable of donating H+) and all basic (capable of adding H+) functional groups are in a dissociated state.

Therefore, in a neutral environment, amino acids containing a non-dissociating radical have a total charge of zero. Amino acids containing acidic functional groups have a total negative charge, and amino acids containing basic functional groups have a positive charge (Table 1-3).

A change in pH toward the acidic side (i.e., an increase in the H+ concentration in the medium) leads to suppression of the dissociation of acid groups. In a highly acidic environment, all amino acids acquire a positive charge.

On the contrary, an increase in the concentration of OH- groups causes the elimination of H+ from the main functional groups, which leads to a decrease in the positive charge. In a highly alkaline environment, all amino acids have a net negative charge.

5. Modified amino acids present in proteins

Only the 20 listed amino acids take part directly in the synthesis of proteins in the human body. However, some proteins contain non-standard modified amino acids - derivatives of one of these 20 amino acids. For example, the molecule of collagen (fibrillar protein of the intercellular matrix) contains hydroxy derivatives of lysine and proline - 5-hydroxylysine and 4-hydroxyproline.

Modifications of amino acid residues are already carried out in the composition of proteins, i.e. only

Modified amino acids found in proteins

after completion of their synthesis. The introduction of additional functional groups into the structure of amino acids gives proteins properties

Scheme. Structure of polar charged amino acids in dissociated form

Table 1-3. Change in the total charge of amino acids depending on the pH of the environment

necessary for them to perform specific functions. Thus, α-carboxyglutamic acid is part of the proteins involved in blood coagulation, and two closely located carboxyl groups in their structure are necessary for the binding of protein factors with Ca2+ ions. Impaired carboxylation of glutamate leads to decreased blood clotting.

6. Chemical reactions used to detect amino acids

The ability of amino acids to enter into certain chemical reactions is determined by the presence of functional groups in their composition. Since all amino acids that make up proteins contain amino and carboxyl groups at the α-carbon atom, they can enter into chemical reactions characteristic of all amino acids. The presence of any functional groups in the radicals of individual amino acids determines their ability to enter into reactions specific to these amino acids.

Ninhydrin reaction to α-amino acids

The ninhydrin reaction can be used to detect and quantify amino acids in solution.

This reaction is based on the fact that colorless ninhydrin, reacting with an amino acid, condenses in the form of a dimer through a nitrogen atom removed from the α-amino group of the amino acid. As a result, a red-violet pigment is formed. At the same time, decarboxylation of the amino acid occurs, which leads to the formation of CO2 and the corresponding aldehyde. The ninhydrin reaction is widely used in studying the primary structure of proteins (see diagram below).

Since the color intensity is proportional to the amount of amino acids in the solution, it is used to measure the concentration of α amino acids.

Ninhydrin reaction used to determine α amino acids

Specific reactions to individual amino acids

Qualitative and quantitative determination of individual amino acids is possible due to the presence of special functional groups in their radicals.

Arginine is determined using a qualitative reaction to the guanidine group (Sakaguchi reaction), and cysteine ​​is detected by the Foll reaction, specific to the SH group of a given amino acid. The presence of aromatic amino acids in a solution is determined by the xanthoprotein reaction (nitration reaction), and the presence of a hydroxyl group in the aromatic ring of tyrosine is determined by the Millon reaction.

B. Peptide bond. Structure and biological properties of peptides

α-Amino acids can be covalently linked to each other using peptide bonds. A peptide bond is formed between the α-carboxyl group of one amino acid and the α-amino group of another, i.e. is an amide bond. In this case, a water molecule is split off (see diagram A).

1. Peptide structure

The number of amino acids in peptides can vary greatly. Peptides containing up to 10 amino acids are called oligopeptides. Often the name of such molecules indicates the number of amino acids included in the oligopeptide: tripeptide, pentapeptide, ocgapeptide, etc.

Peptides containing more than 10 amino acids are called "polypeptides", and polypeptides consisting of more than 50 amino acid residues are usually called proteins. However, these names are conditional, since in the literature the term “protein” is often used to designate a polypeptide containing less than 50 amino acid residues. For example, the hormone glucagon, consisting of 29 amino acids, is called a protein hormone.

The monomers of amino acids that make up proteins are called "amino acid residues". An amino acid residue that has a free amino group is called N-terminal and is written on the left, and one that has a free?-carboxyl group is called C-terminal and is written on the right. Peptides are written and read from the N-terminus. A chain of repeating atoms in a polypeptide chain -NH-CH-CO- is called "peptide backbone"(see diagram B).

When naming a polypeptide, the suffix -yl is added to the abbreviated name of amino acid residues, with the exception of the C-terminal amino acid. For example, the tetrapeptide Ser-Gly-Pro-Ala is read as serylglycylprolylalanine.

The peptide bond formed by the imino group of proline differs from other peptide bonds because the nitrogen atom of the peptide group is not bonded to hydrogen, but to a radical.

Peptides differ in amino acid composition, number and order of amino acids.

Serylglycylprolylalanine

Scheme A. Dipeptide formation

Scheme B. Structure of peptides

Ser-Gis-Pro-Ala and Ala-Pro-Gis-Ser are two different peptides, despite the fact that they have the same quantitative and qualitative amino acid compositions.

2.Characteristics of peptide bond

The peptide bond has the characteristic of a partial double bond, so it is shorter than the other bonds of the peptide backbone and, as a result, has little mobility. The electronic structure of the peptide bond determines the flat, rigid structure of the peptide group. The planes of the peptide groups are located at an angle to each other (Fig. 1-1).

The bond between the α carbon atom and the α-amino group or α-carboxyl group is freely rotatable (although limited by the size and nature of the radicals), allowing the polypeptide chain to adopt different configurations.

Peptide bonds are usually located in the trans configuration, i.e. α-carbon atoms are located on opposite sides of the peptide bond. As a result, the side radicals of amino acids are located at the furthest distance from each other in space (Fig. 1-2).

Peptide bonds are very strong and do not spontaneously break under normal conditions existing in cells (neutral environment, body temperature). In laboratory conditions, the hydrolysis of protein peptide bonds is carried out in a sealed ampoule with concentrated (6 mol/l) hydrochloric acid, at a temperature of more than 105 ° C, and complete hydrolysis of the protein to free amino acids takes place in about a day.

In living organisms, peptide bonds in proteins are broken with the help of special proteolytic enzymes (from English, protein - protein, lysis - destruction), also called proteases, or peptide hydrolases.

To detect proteins and peptides in solution, as well as for their quantitative determination, the biuret reaction is used (a positive result for substances containing at least two peptide bonds).

3.Biological role of peptides

The human body produces many peptides that participate in the regulation of various biological processes and have high physiological activity.

Rice. 1-1. Planes of location of peptide groups and α-carbon atoms in space.

Rice. 1-2. Trans configuration of peptide bonds. Functional groups-CO- and -NH-,

forming peptide bonds, are not ionized, but are polar, and can participate in the formation of hydrogen bonds.

The number of amino acid residues in the structure of biologically active peptides can vary from 3 to 50. Some of the “smallest” peptides include thyrotropin-releasing hormone and glutathione (tripeptides), as well as enkephalins, which contain 5 amino acids. However, most biologically active peptides contain more than 10 amino acids, for example, neuropeptide Y (appetite regulator) contains 36 amino acids, and corticoliberin - 41 amino acids.

Some of the peptides, in particular most peptide hormones, contain peptide bonds formed by the α-amino group and the α-carboxyl group of neighboring amino acids. Typically, they are synthesized from inactive protein precursors in which specific proteolytic enzymes break down specific peptide bonds.

Angiotensin II is an octapeptide formed from the large plasma protein angiotensinogen as a result of the sequential action of two proteolytic enzymes.

The first proteolytic enzyme, renin, cleaves from angiotensinogen from the N-terminus a peptide containing 10 amino acids, called angiotensin I. The second proteolytic enzyme, carboxydipeptidyl peptidase, cleaves from the C-terminus

PROTEIN BIOSYNTHESIS ON RIBOSOME

Amino acids - (aminocarboxylic acids; amc) - organic compounds, V the molecule of which simultaneously containscarboxyl And amine groups (amino groups). Those. Aamino acids may be considered, as derivatives of carboxylic acids in which one or more hydrogen atoms are replaced by amino groups.

• Carboxyl group (carboxyl)-COOH is a functional monovalent group that is part of carboxylic acids and determines their acidic properties.
• Amino group - functional chemical monovalent group -NH 2,an organic radical containing one nitrogen atom and two hydrogen atoms.

More than 200 natural amino acids are known, which can be classified in different ways. Structural classification is based on the position of functional groups at the alpha, beta, gamma or delta position of the amino acid.

In addition to this classification, there are others, for example, classification by polarity, pH level, and also the type of side chain group (aliphatic, acyclic, aromatic amino acids, amino acids containing hydroxyl or sulfur, etc.).

In the form of proteins, amino acids are the second (after water) component of muscles, cells and other tissues of the human body. Amino acids play a critical role in processes such as neurotransmitter transport and biosynthesis.

General structure of amino acids. Alpha amino acids. Isomerization of amino acids.

Amino acids- biologically important organic compounds consisting of an amino group (-NH 2) and a carboxylic acid (-COOH), and having a side chain specific to each amino acid. The key elements of amino acids are carbon, hydrogen, oxygen and nitrogen. Other elements are found on the side chain of certain amino acids.

Rice. 1 - General structure of α-amino acids that make up proteins (except proline). The components of an amino acid molecule are the amino group NH 2, the carboxyl group COOH, the radical (different for all α-amino acids), the α-carbon atom (in the center).

In the structure of amino acids, the side chain specific to each amino acid is designated by the letter R. The carbon atom adjacent to the carboxyl group is called an alpha carbon, and amino acids whose side chain is linked to this atom are called alpha amino acids. They are the most common form of amino acids found in nature.

In alpha amino acids, with the exception of glycine, the alpha carbon is a chiral carbon atom. Amino acids whose carbon chains are attached to an alpha carbon (such as Lysine (L-lysine)) have carbons designated alpha, beta, gamma, delta, and so on. Some amino acids have an amino group attached to the beta or gamma carbon and are therefore called beta or gamma amino acids.

Based on the properties of their side chains, amino acids are divided into four groups. The side chain can make the amino acid a weak acid, a weak base, or an emulsoid (if the side chain is polar), or a hydrophobic substance that does not absorb water well (if the side chain is nonpolar).

The term "branched chain amino acid" refers to amino acids that have aliphatic non-linear side chains, these are Leucine, Isoleucine and Valine.

Proline is the only proteinogenic amino acid whose side group is attached to the alpha amino group and is thus also the only proteinogenic amino acid containing a secondary amine at this position. In chemical terms, proline is thus an imino acid, since it lacks a primary amino group, although in current biochemical nomenclature it is still classified as an amino acid as well as an "N-alkylated alpha amino acid" ( Imino acids- carboxylic acids containing an imino group (NH). They are part of proteins; their metabolism is closely related to the metabolism of amino acids. In their properties, imino acids are close to amino acids, and as a result of catalytic hydrogenation, imino acids are converted into amino acids.Imino group— molecular group NH. Bivalent. Contained in secondary aminah and peptides. The divalent ammonia radical does not exist in its free form).

ALPHA AMINO ACIDS

Amino acids, having both an amine and a carboxyl group, are attached to the first (alpha) carbon atom and are of particular importance in biochemistry. They are known as 2-, alpha, or alpha-amino acids (the general formula in most cases is H 2 NCHRCOOH, where R represents an organic substituent known as a "side chain"); often the term "amino acid" refers specifically to them.

These are 22 proteinogenic (that is, “protein-building”) amino acids that are combined into peptide chains (“polypeptides”), ensuring the construction of a wide range of proteins. They are L-stereoisomers ("left-handed" isomers), although some of the D-amino acids ("right-handed" isomers occur in some bacteria and some antibiotics).

Rice. 2. Peptide bond is a type of amide bond that occurs during the formation of proteins and peptides as a result of the interaction of the α-amino group (-NH 2) of one amino acid with the α-carboxyl group (-COOH) of another amino acid.

From two amino acids (1) and (2) a dipeptide (a chain of two amino acids) and a water molecule are formed. According to the same schemeribosomegenerates longer chains of amino acids: polypeptides and proteins. Different amino acids, which are the “building blocks” of protein, differ in the R radical.

OPTICAL ISOMERISM OF AMINO ACIDS

Rice. 3. Optical isomers of the amino acid alanine

Depending on the position of the amino group relative to the 2nd carbon atom, α-, β-, γ- and other amino acids are distinguished. For the mammalian body, α-amino acids are most characteristic. All α-amino acids found in living organisms, exceptglycine, contain an asymmetric carbon atom(threonine And isoleucinecontain two asymmetric atoms) and have optical activity. Almost all naturally occurring α-amino acids have an L-configuration, and only L-amino acids are included in proteins synthesized in ribosomes.

All standard alpha amino acids, except glycine, can exist in one of two forms enantiomers , called L or D amino acids, which are mirror images of each other.

D, L - Designation system for stereoisomers.

According to this system, the L-configuration is assigned to a stereosomer, in which in the Fischer projection the reference group is located to the left of the vertical line (from the Latin “laevus” - left). We must remember that in Fischer projections the most oxidized carbon atom is located at the top (as a rule, this atom is part of the carboxyl COOH or carbonyl CH=O group). In addition, in the Fisher projection, all horizontal connections are directed towards the observer, and vertical connections are removed from the observer. Accordingly, if reference group located in the Fischer projection on the right, the stereoisomer has a D configuration (from the Latin “dexter” - right).In α-amino acids reference groups NH 2 groups serve.

Enantiomers - pairstereoisomers, which are mirror reflections of each other, not compatible in space. A classic illustration of two enantiomers is the right and left palms: they have the same structure, but different spatial orientation.The existence of enantiomeric forms is associated with the presence of a molecule chirality - properties of not being combined in space with its mirror image..

Enantiomers are identical in physical properties. They can be distinguished only when interacting with a chiral environment, for example, light radiation. Enantiomers behave identically in chemical reactions with achiral reagents in an achiral environment. However, if the reagent, catalyst, or solvent is chiral, the reactivity of the enantiomers tends to differ.Most chiral natural compounds (amino acids, monosaccharides) exists as 1 enantiomer.The concept of enantiomerism is important in pharmaceuticals because different enantiomers of drugs have different biological activity.

PROTEIN BIOSYNTHESIS ON RIBOSOME

STANDARD AMINO ACIDS

(proteinogenic)

See on topic: and Structure of proteinogenic amino acids

During the process of protein biosynthesis, 20 α-amino acids, encoded by the genetic code, are included in the polypeptide chain (see Fig. 4). In addition to these amino acids, called proteinogenic, or standard, some proteins contain specific non-standard amino acids that arise from standard ones during the process of post-translational modifications.

Note: Recently, translationally included selenocysteine ​​and pyrrolysine are sometimes considered proteinogenic amino acids. These are the so-called 21st and 22nd amino acids.

Amino acids are the structural compounds (monomers) that make up proteins. They combine to form short polymer chains called long chain peptides, polypeptides or proteins. These polymers are linear and unbranched, with each amino acid in the chain joining two adjacent amino acids.

Rice. 5. Ribosome in the process of translation (protein synthesis)

The process of building a protein is called translation and involves the step-by-step addition of amino acids to the growing protein chain through ribozymes, carried out by the ribosome. The order in which amino acids are added is read into the genetic code using the mRNA template, which is a copy RNA one of the organism's genes.

Translation - protein biosynthesis on the ribosome

Rice. 6 C stages of polypeptide elongation.

Twenty-two amino acids are naturally found in polypeptides and are called proteinogenic, or naturally occurring, amino acids. Of these, 20 are encoded using the universal genetic code.

The remaining 2, selenocysteine ​​and pyrrolysine, are incorporated into proteins through a unique synthetic mechanism. Selenocysteine ​​is formed when the translated mRNA includes a SECIS element causing a UGA codon instead of a stop codon. Pyrrolysine is used by some methanogenic archaea as part of the enzymes needed to produce methane. It is encoded with a UAG codon, which usually acts as a stop codon in other organisms. The UAG codon is followed by a PYLIS sequence.

Rice. 7. Polypeptide chain is the primary structure of a protein.

Proteins have 4 levels of their structural organization: primary, secondary, tertiary and quaternary. Primary structure is the sequence of amino acid residues in a polypeptide chain. The primary structure of a protein is usually described using one-letter or three-letter designations for amino acid residues. Secondary structure is the local ordering of a fragment of a polypeptide chain, stabilized by hydrogen bonds. Tertiary structure is the spatial structure of a polypeptide chain. Structurally, it consists of secondary structure elements stabilized by various types of interactions, in which hydrophobic interactions play a critical role. Quaternary structure (or subunit, domain) - the relative arrangement of several polypeptide chains as part of a single protein complex.

Rice. 8. Structural organization of proteins

NON-STANDARD AMINO ACIDS

(Non-proteinogenic)

In addition to standard amino acids, there are many other amino acids that are called non-proteinogenic or non-standard amino acids. Such amino acids are either not found in proteins (eg L-carnitine, GABA) or are not produced directly in isolation by standard cellular mechanisms (eg hydroxyproline and selenomethionine).

Non-standard amino acids found in proteins are formed by post-translational modification, that is, modification after translation during the process of protein synthesis. These modifications are often necessary for protein function or regulation; for example, carboxylation of glutamate improves the binding of calcium ions, and hydroxylation of proline is important for the maintenance of connective tissue. Another example is the formation of hypusine into the translation initiation factor EIF5A through modification of a lysine residue. Such modifications can also determine the localization of the protein, for example, the addition of long hydrophobic groups can cause the protein to bind to the phospholipid membrane.

Some non-standard amino acids are not found in proteins. These are lanthionine, 2-aminoisobutyric acid, dehydroalanine and gamma-aminobutyric acid. Non-standard amino acids are often found as metabolic intermediates for standard amino acids - for example, ornithine and citrulline occur in the ornithine cycle as part of acid catabolism.

A rare exception to the dominance of alpha amino acids in biology is the beta amino acid Beta-alanine (3-aminopropanoic acid), which is used for the synthesispantothenic acid(vitamin B5), a component of coenzyme A in plants and microorganisms. In particular, it is produced propionic acid bacteria.

Functions of amino acids

PROTEIN AND NON-PROTEIN FUNCTIONS

Many proteinogenic and non-proteinogenic amino acids also play important roles unrelated to protein formation in the body. For example, in the human brain glutamate (standard glutamic acid) and gamma-aminobutyric acid ( GABA, a non-standard gamma amino acid), are the main excitatory and inhibitory neurotransmitters. Hydroxyproline (the main component of collagen connective tissue) is synthesized from parolin; the standard amino acid glycine is used for synthesis porphyrins, used in red blood cells. Non-standard carnitine is used for lipid transport.

Because of their biological significance, amino acids play an important role in nutrition and are commonly used in food additives, fertilizers, and food processing. In industry, amino acids are used in the production of drugs, biodegradable plastics and chiral catalysts.

1. Amino acids, proteins and nutrition

For information on the biological role and consequences of amino acid deficiency in the human body, see the tables of essential and non-essential amino acids.

When introduced into the human body through food, the 20 standard amino acids are either used to synthesize proteins and other biomolecules or are oxidized into urea and carbon dioxide as an energy source. Oxidation begins with the removal of the amino group through transaminase, and then the amino group is included in the urea cycle. Another product of transamidation is a keto acid, which is part of the citric acid cycle. Glucogenic amino acids can also be converted to glucose through gluconeogenesis.

From 20 standard amino acids, 8 (valine, isoleucine, leucine, lysine, methionine, threonine, tryptophan and phenylalanine) are called essential because the human body cannot synthesize them independently from other compounds in the quantities necessary for normal growth; they can only be obtained from food. However, according to modern concepts, Histidine and Arginineare also essential amino acids for children.Others may be conditionally essential for people of a certain age or people with certain diseases.

Besides, Cysteine, Taurine, are considered semi-essential amino acids in children (even though taurine is not technically an amino acid) because the metabolic pathways that synthesize these amino acids are not yet fully developed in children. The required amounts of amino acids also depend on the age and health of the individual, so it is quite difficult to give general dietary recommendations here.

PROTEINS

Squirrels (proteins, polypeptides) - high molecular weight organic matter, consisting of alpha amino acids , connected in a chain peptide bond. In living organisms, the amino acid composition of proteins is determined genetic code, in most cases 20 are used in synthesisstandard amino acids.

Rice. 9. Proteins are not only food... Types of protein compounds.

Every living organism is made up of proteins. Various forms of proteins take part in all processes occurring in living organisms. In the human body, muscles, ligaments, tendons, all organs and glands, hair, nails are formed from proteins; proteins are found in fluids and bones. Enzymes and hormones that catalyze and regulate all processes in the body are also proteins.A deficiency of proteins in the body is dangerous to health. Each protein is unique and exists for specific purposes.

Proteins - an important part nutrition animals and humans (main sources: meat, poultry, fish, milk, nuts, legumes, grains; to a lesser extent: vegetables, fruits, berries and mushrooms), since their bodies cannot synthesize all the necessary amino acids and some must come from protein food. During digestion, enzymes break down consumed proteins into amino acids, which are used for the biosynthesis of the body's own proteins or are further broken down to produce energy.

It is worth emphasizing that modern nutrition science claims that protein should satisfy the body's needs for amino acids not only in quantity. These substances must enter the human body in certain proportions to each other.

The process of protein synthesis occurs constantly in the body. If at least one essential amino acid is missing, protein formation stops.This can lead to a variety of serious health problems, from digestive disorders to depression and stunted growth in children. Of course, this consideration of the issue is very simplified, because The functions of proteins in the cells of living organisms are more diverse than the functions of other biopolymers - polysaccharides and DNA.

Also, in addition to proteins, amino acids form a large number of non-protein substances (see below) that perform special functions. These include, for example, choline (a vitamin-like substance that is part of phospholipids and is a precursor to the neurotransmitter acetylcholine - Neurotransmitters are chemical substances that transmit nerve impulses from one nerve cell to another. Thus, some amino acids are essential for normal brain function) .

2. Non-protein functions of amino acids

Amino acid neurotransmitter

Note: Neurotransmitters (neurotransmitters, intermediaries) are biologically active chemical substances through which an electrochemical impulse is transmitted from a nerve cell through the synaptic space between neurons, and also, for example, from neurons to muscle tissue or glandular cells. To receive information from its own tissues and organs, the human body synthesizes special chemicals - neurotransmitters.All internal tissues and organs of the human body, “subordinate” to the autonomic nervous system (ANS), are supplied with nerves (innervated), i.e., the functions of the body are controlled by nerve cells. They, like sensors, collect information about the state of the body and transmit it to the appropriate centers, and from them corrective influences go to the periphery. Any violation of autonomic regulation leads to malfunctions of internal organs. The transfer of information, or control, is carried out with the help of special chemical intermediaries, which are called mediators (from the Latin mediator - intermediary) or neurotransmitters. By their chemical nature, mediators belong to different groups: biogenic amines, amino acids, neuropeptides, etc. Currently, more than 50 compounds related to mediators have been studied.

In the human body, many amino acids are used to synthesize other molecules, for example:

• Tryptophan is a precursor to the neurotransmitter serotonin.

• L-Tyrosine and its precursor phenylalanine are precursors to the neurotransmitters dopamine catecholamines, epinephrine and norepinephrine.
  

• Glycine is a precursor to porphyrins such as heme.
  

• Arginine is a precursor to nitric oxide.
  

• Ornithine and S-adenosylmethionine are precursors to polyamines.
  

• Aspartate, glycine and glutamine are nucleotide precursors.
  

However, not all functions of the other numerous non-standard amino acids. Some non-standard amino acids are used by plants to defend against herbivores. For example, canavanine is an analogue of arginine, which is found in many legumes, and in particularly large quantities in Canavalia gladiata. This amino acid protects plants from predators such as insects and can cause illness in humans when some unprocessed legumes are consumed.

Classification of proteinogenic amino acids

Let's consider the classification using the example of 20 proteinogenic α-amino acids necessary for protein synthesis

Among the variety of amino acids, only 20 are involved in intracellular protein synthesis (proteinogenic amino acids). Also, about 40 more non-proteinogenic amino acids have been found in the human body.All proteinogenic amino acids are α-amino acids. Their example can be used to show additional classification methods. Amino acid names are usually abbreviated to a 3-letter designation (see polypeptide chain picture at the top of the page). Molecular biology professionals also use single-letter symbols for each amino acid.

1. According to the structure of the side radical highlight:

• aliphatic (alanine, valine, leucine, isoleucine, proline, glycine) - compounds that do not contain aromatic bonds.
  
• aromatic (phenylalanine, tyrosine, tryptophan)

• sulfur-containing (cysteine, methionine) containing a sulfur atom S
  
• containing OH group (serine, threonine, tyrosine again),
• containing additional COOH group(aspartic and glutamic acids),
• additional NH 2 group(lysine, arginine, histidine, also glutamine, asparagine).

2. According to the polarity of the side radical

There are non-polar amino acids (aromatic, aliphatic) and polar (uncharged, negatively and positively charged).

3. According to acid-base properties

According to their acid-base properties, they are divided into neutral (most), acidic (aspartic and glutamic acids) and basic (lysine, arginine, histidine) amino acids.

4. By irreplaceability

As necessary for the body, those that are not synthesized in the body and must be supplied with food are isolated - essential amino acids (leucine, isoleucine, valine, phenylalanine, tryptophan, threonine, lysine, methionine). Replaceable amino acids include those amino acids whose carbon skeleton is formed in metabolic reactions and is capable of somehow obtaining an amino group to form the corresponding amino acid. Two amino acids are conditionally essential (arginine, histidine), i.e. their synthesis occurs in insufficient quantities, especially for children.

Table 1. Classification of amino acids

It's no secret that in order to maintain vital functions at a high level, a person needs protein - a kind of building material for body tissues; Proteins contain 20 amino acids, the names of which are unlikely to mean anything to the average office worker. Every person, especially if we talk about women, has at least once heard about collagen and keratin - these are proteins that are responsible for the appearance of nails, skin and hair.

Amino acids - what are they?

Amino acids (or aminocarboxylic acids; AMK; peptides) are organic compounds consisting of 16% amines - organic derivatives of ammonium - which distinguishes them from carbohydrates and lipids. They participate in the biosynthesis of protein by the body: in the digestive system, under the influence of enzymes, all proteins supplied with food are destroyed to AMC. In total, there are about 200 peptides in nature, but only 20 basic amino acids are involved in the construction of the human body, which are divided into replaceable and essential; sometimes there is a third type - semi-replaceable (conditionally replaceable).

Nonessential amino acids

Replaceable amino acids are those that are both consumed in food and reproduced directly in the human body from other substances.

• Alanine is a monomer of biological compounds and proteins. It carries out one of the main pathways of glucogenesis, that is, it is converted into glucose in the liver, and vice versa. A highly active participant in metabolic processes in the body.
• Arginine is an amino acid that can be synthesized in the body of an adult, but is not capable of synthesis in the body of a child. Promotes the production of growth hormones and others. The only carrier of nitrogenous compounds in the body. Helps increase muscle mass and reduce fat mass.
• Asparagine is a peptide involved in nitrogen metabolism. During the reaction with the enzyme asparaginase, it splits off ammonia and turns into aspartic acid.
• Aspartic acid - takes part in the creation of immunoglobulin, deactivates ammonia. Necessary for malfunctions of the nervous and cardiovascular systems.
• Histidine - used for the prevention and treatment of gastrointestinal diseases; has positive dynamics in the fight against AIDS. Protects the body from the harmful effects of stress.
• Glycine is a neurotransmitter amino acid. Used as a mild sedative and antidepressant. Enhances the effect of some nootropic drugs.
• Glutamine - in large quantities Activator of tissue repair processes.
• Glutamic acid - has a neurotransmitter effect and also stimulates metabolic processes in the central nervous system.
• Proline is one of the components of almost all proteins. They are especially rich in elastin and collagen, which are responsible for skin elasticity.
• Serine is an amino acid that is found in neurons of the brain and also contributes to the release of large amounts of energy. It is a derivative of glycine.
• Tyrosine is a component of animal and plant tissues. Can be reproduced from phenylalanine by the action of the enzyme phenylalanine hydroxylase; the reverse process does not occur.
• Cysteine ​​is one of the components of keratin, which is responsible for the firmness and elasticity of hair, nails, and skin. It is also an antioxidant. Can be produced from serine.

Amino acids that cannot be synthesized in the body are essential

Essential amino acids are those that cannot be generated in the human body and can only be supplied through food.

• Valine is an amino acid found in almost all proteins. Increases muscle coordination and reduces the body's sensitivity to temperature changes. Maintains the hormone serotonin at high levels.
• Isoleucine is a natural anabolic steroid that, through the process of oxidation, saturates muscle and brain tissue with energy.
• Leucine is an amino acid that improves metabolism. It is a kind of “builder” of protein structure.
• These three AMKs are part of the so-called BCAA complex, which is especially in demand among athletes. Substances in this group act as a source for increasing muscle mass, reducing fat mass and maintaining good health during particularly intense physical activity.
• Lysine is a peptide that accelerates tissue regeneration, the production of hormones, enzymes and antibodies. Responsible for the strength of blood vessels, found in muscle protein and collagen.
• Methionine - takes part in the synthesis of choline, the lack of which can lead to increased accumulation of fat in the liver.
• Threonine - gives elasticity and strength to tendons. It has a very positive effect on the heart muscle and tooth enamel.
• Tryptophan - supports emotional state, as it is converted into serotonin in the body. Indispensable for depression and other psychological disorders.
• Phenylalanine - improves the appearance of the skin by normalizing pigmentation. Supports psychological well-being by improving mood and bringing clarity to thinking.

Other methods for classifying peptides

Scientifically, the 20 essential amino acids are divided based on the polarity of their side chains, or radicals. Thus, four groups are distinguished: (but not having a charge), positively charged and negatively charged.

Non-polar are: valine, alanine, leucine, isoleucine, methionine, glycine, tryptophan, phenylalanine, proline. In turn, polar acids that have a negative charge include aspartic and glutamic acids. Polar, having a positive charge, are called arginine, histidine, lysine. Amino acids that have polarity but do not have a charge include cysteine, glutamine, serine, tyrosine, threonine, and asparagine.

20 amino acids: formulas (table)

Based on this, it can be noted that all 20 in the table above) contain carbon, hydrogen, nitrogen and oxygen.

Amino acids: participation in cell activity

Aminocarboxylic acids are involved in the biological synthesis of protein. Protein biosynthesis is the process of modeling a polypeptide (“poly” - many) chain of amino acid residues. The process takes place on the ribosome, an organelle inside the cell that is directly responsible for biosynthesis.

Information is read from a section of the DNA chain according to the principle of complementarity (A-T, C-G); when creating m-RNA (messenger RNA, or i-RNA - information RNA - identical concepts), the nitrogenous base thymine is replaced by uracil. Then, using the same principle, a transporting amino acid molecules to the place of synthesis is created. T-RNA is encoded by triplets (codons) (example: UAU), and if you know what nitrogenous bases a triplet is represented by, you can find out which amino acid it carries.

Food groups with the highest content of AMK

Dairy products and eggs contain important substances such as valine, leucine, isoleucine, arginine, tryptophan, methionine and phenylalanine. Fish and white meat have a high content of valine, leucine, isoleucine, histidine, methionine, lysine, phenylalanine, tryptophan. Legumes, grains and cereals are rich in valine, leucine, isoleucine, tryptophan, methionine, threonine, methionine. Nuts and various seeds will saturate the body with threonine, isoleucine, lysine, arginine and histidine.

Below is the amino acid content of some foods.

The largest amount of tryptophan and methionine can be found in hard cheese, lysine - in rabbit meat, valine, leucine, isoleucine, threonine and phenylalanine - in soy. When creating a diet based on maintaining normal BUN, you should pay attention to squid and peas, while the poorest in terms of peptide content are potatoes and cow's milk.

Lack of amino acids in vegetarianism

It is a myth that there are amino acids that are found exclusively in animal products. Moreover, scientists have found that plant protein is absorbed by the human body better than animal protein. However, when choosing vegetarianism as a lifestyle, it is very important to monitor your diet. The main problem is that one hundred grams of meat and the same amount of beans contain different amounts of BUN in percentage terms. At first, it is necessary to keep track of the amino acid content in the food consumed, then this should become automatic.

How many amino acids should you consume per day?

In the modern world, absolutely all food products contain the nutrients necessary for humans, so there is no need to worry: all 20 protein amino acids are safely supplied from food, and this amount is enough for a person who leads a normal lifestyle and at least slightly monitors his diet.

An athlete’s diet must be saturated with proteins, because without them it is simply impossible to build muscle mass. Physical exercise leads to a colossal consumption of amino acid reserves, so professional bodybuilders are forced to take special supplements. With intensive building of muscle relief, the amount of protein can reach up to one hundred grams of protein per day, but such a diet is not suitable for daily consumption. Any food supplement implies instructions containing different AMKs in doses, which must be read before using the drug.

The influence of peptides on the quality of life of an ordinary person

The need for proteins is present not only among athletes. For example, the proteins elastin, keratin, and collagen affect the appearance of hair, skin, nails, as well as the flexibility and mobility of joints. A number of amino acids affect the body, maintaining fat balance at an optimal level, providing sufficient energy for everyday life. After all, in the process of life, even with the most passive lifestyle, energy is expended, at least for breathing. In addition, cognitive activity is also impossible when there is a lack of certain peptides; maintaining the psycho-emotional state is carried out, among other things, by AMK.

Amino acids and sports

The diet of professional athletes involves a perfectly balanced diet that helps maintain muscle tone. Designed specifically for those athletes who are working on gaining muscle mass, they make life much easier.

As previously written, amino acids are the main building blocks of proteins necessary for muscle growth. They are also able to speed up metabolism and burn fat, which is also important for beautiful muscle definition. When training hard, it is necessary to increase your BUN intake due to the fact that they increase the rate of muscle building and reduce post-workout pain.

The 20 amino acids in proteins can be consumed both as part of aminocarbon complexes and from food. If you choose a balanced diet, then you need to take into account absolutely all grams, which is difficult to implement when the day is very busy.

What happens to the human body when there is a lack or excess of amino acids

The main symptoms of amino acid deficiency are: poor health, lack of appetite, brittle nails, increased fatigue. Even with a lack of BUN alone, a huge number of unpleasant side effects occur, which significantly impair well-being and productivity.

Oversaturation with amino acids can lead to disruptions in the functioning of the cardiovascular and nervous systems, which, in turn, is no less dangerous. In turn, symptoms similar to food poisoning may appear, which also does not entail anything pleasant.

You need to know moderation in everything, so maintaining a healthy lifestyle should not lead to an excess of certain “useful” substances in the body. As the classic wrote, “the best is the enemy of the good.”

In the article we looked at the formulas and names of all 20 amino acids; the table of the content of the main AMAs in products is given above.

Amino acids are heterofunctional compounds that necessarily contain two functional groups: an amino group - NH 2 and a carboxyl group - COOH, associated with a hydrocarbon radical. The general formula of the simplest amino acids can be written as follows:

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

Properties of amino acids

The amino group - NH 2 determines the basic properties of amino acids, since it is capable of attaching a hydrogen cation to itself via a donor-acceptor mechanism due to the presence of a free electron pair at the nitrogen atom.

The -COOH group (carboxyl group) determines the acidic properties of these compounds. Therefore, amino acids are amphoteric organic compounds. They react with alkalis as acids:

With strong acids - like bases - amines:

In addition, the amino group in an amino acid interacts with its carboxyl group, forming an internal salt:

The ionization of amino acid molecules depends on the acidic or alkaline nature of the environment:

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

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

Amino acids are divided into 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-shapes. About half of these amino acids are irreplaceable, because they are not synthesized in the human body. Essential acids are valine, leucine, isoleucine, phenylalanine, lysine, threonine, cysteine, methionine, histidine, tryptophan. These substances enter the human body with food. If their quantity in food is insufficient, the normal development and functioning of the human body is disrupted. In certain diseases, the body is unable to synthesize some other amino acids. Thus, in phenylketonuria, tyrosine is not synthesized. The most important property of amino acids is the ability to enter into molecular condensation with the release of water and the formation of the amide group -NH-CO-, for example:

The high-molecular compounds obtained as a result of this reaction contain a large number of amide fragments and are therefore called polyamides.

These, in addition to the synthetic nylon fiber mentioned above, include, for example, enant, formed during the polycondensation of aminoenanthic acid. Amino acids with amino and carboxyl groups at the ends of the molecules are suitable for producing synthetic fibers.

Alpha amino acid polyamides are called peptides. Depending on the number of amino acid residues, they are distinguished dipeptides, tripeptides, polypeptides. In such compounds, the -NH-CO- groups are called peptide groups.