“Amino acids structure, classification, properties, biological role. CO2 at the conversion stage

Makaseeva O.N., Dudinskaya O.V., Tkachenko L.M., Ilyicheva N.I.

R... Biological chemistry. Section “Proteins and Nucleic Acids”: lecture notes / O.N. Makaseeva, O.V. Dudinskaya, L.M. Tkachenko, N.I. Ilyicheva. – Mogilev: MGUP, 2014. – …… p.

ISBN……978-985-6979-70-8……

ISBN…….978-985-6979-69-2.

Lecture notes on the discipline “Biological chemistry”. The section “Proteins and Nucleic Acids” is an additional source that will help students of all forms of study master this discipline. Lecture notes contain the main topics of the “Proteins and Nucleic Acids” section of the course in accordance with the curriculum.

Intended for students of technological specialties in the food industry.

UDC…. 547

BBK.... 24.2

1 AMINO ACIDS.. 4

1.1 Structure of amino acids. 4

1.2 Classification of amino acids. 7

1.3 General properties of amino acids. 9

1.3.1 Optical properties. 9

1.3.2 Acid-base properties of amino acids. Isoelectric point. 10

1.3.1 Chemical properties of amino acids. 14

1.3.2 Melanoid formation reaction. 14

2 PEPTIDES.. 16

3 PROTEINS.. 20

3.1 Functions of proteins. 20

3.2 The structure of a protein molecule.. 23

3.3 Physico-chemical properties of proteins. 34

3.3.1 Amphoteric properties of proteins. Isoelectric point of proteins. 34

3.3.2 Denaturation of proteins. 34

3.3.3 Hydrophilic properties of proteins. Salting out proteins. 37

3.4 Methods for protein isolation. 40

3.5 Classification of proteins. 43

4 NUCLEIC ACIDS.. 46

4.1 Composition of nucleic acids. 46

4.2 Nucleosides.. 49

4.3 Nucleotides.. 51

4.4 Primary structure of nucleic acids. 54

4.5 Secondary and tertiary structures of DNA... 55

AMINO ACIDS

Amino acid structure

The main structural unit of proteins are a-amino acids. Over 300 amino acids are known in nature, but proteins contain only 20 a-amino acids (one of them, proline, is not amino-, A imino acid), called protein, or proteinogenic, amino acids (see Table 1). All other amino acids exist in a free state or as part of short peptides, or complexes with other organic substances.

a-Amino acids are derivatives of carboxylic acids in which one hydrogen atom at the a-carbon atom is replaced by an amino group (–NH2), for example:

Amino acids differ in the structure and properties of radicals ®. Amino acid radicals can be aliphatic, aromatic and heterocyclic. Thanks to this, each amino acid is endowed with specific properties that determine the chemical, physical properties and physiological functions of proteins in the body.

It is thanks to amino acid radicals that proteins have a number of unique functions not characteristic of other biopolymers and have chemical individuality.

Amino acids with the b- or g-position of the amino group are much less common in living organisms, for example:

In addition to the 20 standard amino acids found in almost all proteins, there are also non-standard amino acids that are components of only some types of proteins - these amino acids are also called modified. About 150 of them have already been allocated. These amino acids are formed after the completion of protein synthesis in the ribosome of cells through post-translational chemical modification.

Table No. 1 – Structure of proteinogenic amino acids

№	Amino acid structure	Abbreviated.	Name
1.		Name	Gli
2.		Glycine	Ala
3.		Alanin	Shaft
4.		Valin	Lei
5.		Leucine	Ile
6.		Isoleucine	Ser
7.		Serin	Tre
8.		Threonine	Cis
9.		Cysteine	Meth
10.		Methionine	Shooting Range
11.		Tyrosine	Hairdryer
12.		Phenylalanine	Three
Tryptophan
13.		Continuation of Table 1	Asp
14.		Aspartic acid	Asn
15.		Asparagine	Glu
16.		Glutamic acid	Gln
17.		Glutamine	Liz
18.		Lysine	Gies
19.		Histidine	Arg
20.		Arginine	About

Proline

One example of a particularly important modification is the oxidation of two-SH groups of cysteine ​​residues to form the amino acid cystine containing a disulfide bond. The reverse transition occurs just as easily.

In this way, one of the most important redox systems of living organisms is formed. Cystine is found in large quantities in cereal proteins - gluten, in hair and horn proteins.

Other examples of amino acid modification are hydroxyproline and hydroxylysine, which are found in collagen, the main protein in animal connective tissue.
Prothrombin protein (blood clotting protein) contains

g-carboxyglutamic acid, and in the enzyme glutathione peroxidase, selenocysteine ​​was discovered, in which (S) sulfur is replaced by (Se) selenium.

Classification of amino acids

There are several types of classifications of amino acids that make up proteins. The basis first

The classification is based on the chemical structure of amino acid radicals. Amino acids are distinguished:– glycine, alanine, valine, leucine, isoleucine, lysine;

- hydroxyl-containing– serine, threonine;

- aromatic– phenylalanine, tyrosine, tryptophan;

- heterocyclic– proline, histidine;

Second The type of classification is based on the polarity of the R groups of amino acids. There are:

- non-polar(hydrophobic) amino acids in which the radical has non-polar bonds between C–C, C–H atoms, there are eight such amino acids: glycine, alanine, valine, leucine, isoleucine, phenylalanine, tryptophan, proline;

- polar uncharged(hydrophilic) amino acids in which the radical has polar bonds between the atoms C–O, C–N, O–H, S–H, there are five such amino acids: serine, threonine, methionine, asparagine, glutamine;

- polar negatively charged amino acids that have groups in the radical that carry a negative charge in an aqueous environment at pH = 7, there are four such amino acids: tyrosine, cysteine, aspartic acid, glutamic acid;

- polar positively charged amino acids that have groups in the radical that carry a positive charge in an aqueous environment at pH = 7; there are three such amino acids: lysine, arginine, histidine.

The more amino acids with polar groups in a protein, the higher its reactivity. The functions of a protein largely depend on its reactivity. Enzymes are characterized by a particularly large number of polar groups. And vice versa, there are very few of them in such a protein as keratin (hair, nails).

Table 2 - Classification of amino acids based on polarity

Third The type of classification is based on the number of amine and carboxyl groups of amino acids. They are divided into monoamine monocarboxylic, containing one carboxyl and amino group each; monoaminodicarboxylic (two carboxyl and one amino group); diaminomonocarboxylic (two amino and one carboxyl group).

Fourth The type of classification is based on the ability of amino acids to be synthesized in humans and animals. All amino acids are divided into essential, essential and partially essential.

Essential amino acids cannot be synthesized in the body of humans and animals; they must be supplied with food. There are eight absolutely essential amino acids: valine, leucine, isoleucine, threonine, tryptophan, methionine, lysine, phenylalanine.

Partially irreplaceable- are synthesized in the body, but in insufficient quantities, so they must be partially supplied with food. These amino acids are arganine and histidine.

Nonessential amino acids are synthesized in the human body in sufficient quantities from other compounds. Plants can synthesize all amino acids.

General properties of amino acids

Optical properties

In the molecules of all natural amino acids (with the exception of glycine), the a-carbon atom has all four valence bonds occupied by various substituents; such a carbon atom is asymmetric and is called a chiral atom. As a result, solutions of amino acids have optical activity - they rotate the plane of plane-polarized light. Moreover, when a polarized beam passes through them, the plane of polarization rotates either to the right (+) or to the left (–). Based on the location of atoms and atomic groups in space relative to an asymmetric atom, they are distinguished L- And D-stereoisomers of amino acids. The sign and magnitude of optical rotation depend on the nature of the amino acid side chain (R-group).

The number of possible stereoisomers is N=2 n, where n is the number of asymmetric carbon atoms. For glycine n = 0, for threonine n = 2. All other 17 protein amino acids contain one asymmetric carbon atom; they can exist in the form of two optical isomers.

As a standard when determining L And D- amino acid configurations, the configuration of stereoisomers of glyceraldehyde is used.

The location in the Fischer projection formula of the NH 2 group on the left corresponds to L-configurations, and on the right – D-configurations.

It should be noted that the letters L And D mean that a substance, in its stereochemical configuration, belongs to L or D row, regardless of the direction of rotation.

Only found in proteins L-isomers of amino acids.
D-forms of amino acids are rare in nature and are found only in the cell wall proteins (glycoproteins) of some bacteria and in peptide antibiotics (gramicidin, actinomycin, etc.). L-forms are well absorbed by plants and animals and are easily included in metabolic processes. D- forms are not assimilated by these organisms, and sometimes even inhibit metabolic processes. This is explained by the fact that the enzymatic systems of organisms are specifically adapted to L forms of amino acids.

L And D forms of amino acids have different physiological effects on the human body - they differ in taste: D- sweet isomers L-forms are bitter or tasteless.

Topic: “Amino acids - structure, classification, properties, biological role”

Amino acids are nitrogen-containing organic compounds whose molecules contain an amino group –NH2 and a carboxyl group –COOH

The simplest representative is aminoethanoic acid H2N - CH2 - COOH

g-carboxyglutamic acid, and in the enzyme glutathione peroxidase, selenocysteine ​​was discovered, in which (S) sulfur is replaced by (Se) selenium.

There are 3 main classifications of amino acids:

Physico-chemical – based on differences in the physicochemical properties of amino acids

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  Hydrophobic amino acids (non-polar). The components of radicals usually contain hydrocarbon groups, where the electron density is evenly distributed and there are no charges or poles. They may also contain electronegative elements, but they are all in a hydrocarbon environment.
• 
  Hydrophilic uncharged (polar) amino acids . The radicals of such amino acids contain polar groups: -OH, -SH, -CONH2
• 
  Negatively charged amino acids. These include aspartic and glutamic acids. They have an additional COOH group in the radical - in a neutral environment they acquire a negative charge.
• 
  Positively charged amino acids : arginine, lysine and histidine. They have an additional NH 2 group (or an imidazole ring, like histidine) in the radical - in a neutral environment they acquire a positive charge.

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  Irreplaceable amino acids, they are also called “essential”. They cannot be synthesized in the human body and must be supplied with food. There are 8 of them and 2 more amino acids that are classified as partially essential.

Partially irreplaceable: arginine, histidine.

• 
  Replaceable(can be synthesized in the human body). There are 10 of them: glutamic acid, glutamine, proline, alanine, aspartic acid, asparagine, tyrosine, cysteine, serine and glycine.

Amino acids are classified according to their structural characteristics.

1. Depending on the relative position of the amino and carboxyl groups, amino acids are divided into α-, β-, γ-, δ-, ε- etc.

The need for amino acids decreases: For congenital disorders associated with the absorption of amino acids. In this case, some protein substances can cause allergic reactions in the body, including problems in the gastrointestinal tract, itching and nausea.
Amino Acid Digestibility

The speed and completeness of absorption of amino acids depends on the type of products containing them. The amino acids contained in egg whites, low-fat cottage cheese, lean meat and fish are well absorbed by the body.

Amino acids are also quickly absorbed with the right combination of products: milk is combined with buckwheat porridge and white bread, all kinds of flour products with meat and cottage cheese.
Beneficial properties of amino acids, their effect on the body

Each amino acid has its own effect on the body. So methionine is especially important for improving fat metabolism in the body; it is used as a prevention of atherosclerosis, cirrhosis and fatty liver degeneration.

For certain neuropsychiatric diseases, glutamine and aminobutyric acids are used. Glutamic acid is also used in cooking as a flavoring additive. Cysteine ​​is indicated for eye diseases.

The three main amino acids - tryptophan, lysine and methionine, are especially necessary for our body. Tryptophan is used to accelerate the growth and development of the body, and it also maintains nitrogen balance in the body.

Lysine ensures normal growth of the body and participates in the processes of blood formation.

The main sources of lysine and methionine are cottage cheese, beef, and some types of fish (cod, pike perch, herring). Tryptophan is found in optimal quantities in offal, veal and game.heart attack.

Amino acids for health, energy and beauty

To successfully build muscle mass in bodybuilding, amino acid complexes consisting of leucine, isoleucine and valine are often used.

To maintain energy during training, athletes use methionine, glycine and arginine, or products containing them, as dietary supplements.

For any person leading an active healthy lifestyle, special foods are needed that contain a number of essential amino acids to maintain excellent physical shape, quickly restore strength, burn excess fat or build muscle mass.

Amino acids (AA) are organic molecules that consist of a basic amino group (-NH 2), an acidic carboxyl group (-COOH), and an organic R radical (or side chain), which is unique to each AA

Amino acid structure

Functions of amino acids in the body

Examples of biological properties of AK. Although more than 200 different AAs occur in nature, only about one tenth of them are incorporated into proteins, others perform other biological functions:

• They are the building blocks of proteins and peptides
• Precursors of many biologically important molecules derived from AK. For example, tyrosine is a precursor to the hormone thyroxine and the skin pigment melanin, and tyrosine is also a precursor to the compound DOPA (dioxyphenylalanine). It is a neurotransmitter for the transmission of impulses in the nervous system. Tryptophan is a precursor to vitamin B3 - nicotinic acid
• Sources of sulfur are sulfur-containing AA.
• AAs are involved in many metabolic pathways, such as gluconeogenesis - the synthesis of glucose in the body, the synthesis of fatty acids, etc.

Depending on the position of the amino group relative to the carboxyl group, AA can be alpha, α-, beta, β- and gamma, γ.

Proteins contain only alpha-AA

General properties of alpha-AA proteins

1 - Optical activity - property of amino acids

All AAs, with the exception of glycine, exhibit optical activity, because contain at least one asymmetric carbon atom (chiral atom).

What is an asymmetric carbon atom? It is a carbon atom with four different chemical substituents attached to it. Why does glycine not exhibit optical activity? Its radical has only three different substituents, i.e. alpha carbon is not asymmetrical.

What does optical activity mean? This means that AA in solution can be present in two isomers. A dextrorotatory isomer (+), which has the ability to rotate the plane of polarized light to the right. Levorotatory isomer (-), which has the ability to rotate the plane of polarization of light to the left. Both isomers can rotate the plane of polarization of light by the same amount, but in the opposite direction.

2 - Acid-base properties

As a result of their ability to ionize, the following equilibrium of this reaction can be written:

R-COOH<------->R-C00-+H+

R-NH2<--------->R-NH 3+

Because these reactions are reversible, this means that they can act as acids (forward reaction) or as bases (reverse reaction), which explains the amphoteric properties of amino acids.

Zwitter ion - property of AK

All neutral amino acids at a physiological pH value (about 7.4) are present as zwitterions - the carboxyl group is unprotonated and the amino group is protonated (Fig. 2). In solutions more basic than the isoelectric point of the amino acid (IEP), the amino group -NH3 + in AA donates a proton. In a solution more acidic than the IET of AA, the carboxyl group -COO - in AA accepts a proton. Thus, AA sometimes behaves like an acid and other times like a base, depending on the pH of the solution.

Polarity as a general property of amino acids

At physiological pH, AA are present as zwitter ions. The positive charge is carried by the alpha amino group, and the negative charge is carried by the carboxylic group. Thus, two opposite charges are created at both ends of the AK molecule, the molecule has polar properties.

The presence of an isoelectric point (IEP) is a property of amino acids

The pH value at which the net electrical charge of an amino acid is zero and, therefore, it cannot move in an electric field is called IET.

The ability to absorb in ultraviolet light is a property of aromatic amino acids

Phenylalanine, histidine, tyrosine and tryptophan absorb at 280 nm. In Fig. The values ​​of the molar extinction coefficient (ε) of these AAs are displayed. In the visible part of the spectrum, amino acids do not absorb, therefore, they are colorless.

AAs can be present in two versions of isomers: L-isomer and D- isomers, which are mirror images and differ in the arrangement of chemical groups around the α-carbon atom.

All amino acids in proteins are in the L-configuration, L-amino acids.

Physical properties of amino acids

Amino acids are mostly water-soluble due to their polarity and the presence of charged groups. They are soluble in polar and insoluble in non-polar solvents.

AKs have a high melting point, which reflects the presence of strong bonds that support their crystal lattice.

Are common The properties of AA are common to all AA and in many cases are determined by the alpha amino group and alpha carboxyl group. AAs also have specific properties that are dictated by their unique side chain.

Amino acids are organic compounds whose molecule simultaneously contains a basic amino group (NH2) and an acidic carboxyl group (COOH). To date, about 200 natural amino acids isolated from animal and plant material have been described. All natural amino acids are divided into two groups: proteinogenic, or proteinaceous (found only in proteins) and non-proteinogenic. s e, or non-protein (not found in proteins). 1. Proteinogenic amino acids. Amino acids found in proteins can be classified according to different criteria. Based on the structure of the side chain (R-group), aliphatic, aromatic and heterocyclic amino acids are distinguished; based on the number of amine and carboxyl groups - monoaminomonocarboxylic (one NH2 group and one COOH group), diaminomonocarboxylic (two NH2 groups and one COOH group ), monoaminodicarboxylic (one NH2 group and two COOH groups), according to the position of the isoelectric point - neutral, basic and acidic. Amino acids containing OH groups in radicals are called hydroxyamino acids, and those containing sulfur are called sulfur-containing acids. Based on their ability to be synthesized in the animal body, biochemists divide amino acids into essential and non-essential. Amino acids containing NH groups instead of NH2 groups are called imino acids.

According to the polarity of R-groups, i.e. the ability of R-groups to interact with water under appropriate intracellular pH conditions (pH around 7.0), amino acids are divided into four groups: with non-polar or hydrophobic R-groups, polar but not charged R-groups, negatively charged R-groups and positively charged R-groups. Let's look at the structure of the amino acids of these groups. Plants and some microorganisms can synthesize all the amino acids they need to build cellular proteins. An animal organism is able to synthesize only about half of the amino acids it needs to build the proteins of its body. These amino acids are called interchangeable amino acids. The remaining ten proteinogenic amino acids cannot be synthesized by animal organisms and must be obtained from food. These amino acids are called essential or essential. These include: valine, isoleucine, methionine, leucine, lysine, threonine, tryptophan, phenylalanine, arginine and histidine. The absence or deficiency of any essential amino acids in food leads to life-threatening phenomena (growth retardation, protein biosynthesis disorder, disease, etc.).

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  Amino acids, found in proteins, can be classified according to different criteria. Based on the structure of the side chain (R-group), aliphatic...


• 
  Amino acids and their properties. Protein molecules are made up of smaller molecules amino acids. Over 170 different amino acids...


• 
  Sources and ways of use amino acids in cells.
  Amino acids determine the biological specificity of proteins and their nutritional value.


• 
  Classification amino acids. 1. According to the ability of radicals to interact with H 2O: - non-polar (hydrophobic) - poorly soluble


• 
  Amino acids- protein monomers, organic carboxylic acids, in which at least one of the hydrogen atoms of the hydrocarbon chain is replaced by an amino group.


• 
  The most important in nutrition are the irreplaceable amino acids, which cannot be synthesized in the body and come only from the outside - with food.


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  Protein usually contains both acidic and alkaline amino acids, so the protein molecule has both positive and negative charges.

BIOCHEMISTRY AS A SCIENCE. STAGES OF BIOCHEMISTRY DEVELOPMENT. METHODS OF BIOCHEMICAL RESEARCH

Biological chemistry is a fundamental biomedical science that studies the chemical composition of living organisms and the chemical transformations of biomolecules.

Studying in the biochemistry course the molecular organization of the cell, the mechanisms of regulation of biochemical reactions that underlie the physiological functions of the human body in health and disease, is of great importance for the development of methods and techniques for the pharmacological correction of impaired metabolic processes.

Basic theoretical questions that allow you to carry out the target activities:

1. Subject and tasks of biological chemistry

1.1. The place of biochemistry among other biomedical disciplines.

1.2. Objects of study and tasks of biochemistry

2. Main stages in the development of biological chemistry as a science

3. Sections of biochemistry:

4. Modern directions of development of biochemistry

4.1. Achievements and prospects for the development of biochemistry, theoretical and molecular biology, biotechnology, genetic engineering and their significance for the diagnosis and treatment of major human diseases - cardiovascular, oncological, infectious and others.

4.2. The role of biochemistry in elucidating the molecular genetic mechanisms of disease pathogenesis, elucidating the significance of hereditary and environmental factors in the occurrence of pathological conditions and their impact on the life expectancy of the population.

5. Biochemical laboratory tests

5.1. Purpose of biochemical research

5.2. Criteria for evaluating the laboratory research method used

5.3. Material for diagnostic studies, principles of material collection

5.4. Errors that occur during laboratory tests

Graph logical structure

Basic terms and their meaning:

Static biochemistry(connection with bioorganic chemistry, molecular biology) studies the chemical composition of organisms.

Dynamic biochemistry studies the transformation of chemical compounds and related energy transformations in the process of life.

Functional biochemistry clarifies the connections between the structure of chemical compounds and the processes of their modification, on the one hand, and the function of subcellular particles of specialized cells, tissues or organs that include the mentioned substances, on the other.

Medical biochemistry(human biochemistry).

Clinical biochemistry as a branch of medical biochemistry

Bioenergy– a branch of dynamic biochemistry that studies the patterns of release, accumulation and use of energy in biological systems.

Molecular genetics– a branch of biochemistry that reveals the patterns of preservation and implementation of genetic information by studying the structure and functioning of information molecules – DNA and RNA.

Electrophoresis– a physicochemical method of analysis used in biochemistry to separate protein fractions.

GENERAL REGULARITIES OF METABOLISM. METABOLISM OF CARBOHYDRATES, LIPIDS, PROTEINS AND ITS REGULATION

INTRODUCTION

Metabolism is a complex system of chemical reactions interconnected through plastic components, energy supply and general regulators. The goals of these reactions are the extraction of energy and the synthesis of biological macromolecules, the structure of which corresponds to the individual genetic program of the organism.

The biochemical metabolic scheme includes chains, cascades and cycles of chemical transformations that together constitute metabolic pathways. In order for these metabolic pathways to function in concert to meet the needs of individual cells, organs, or the body as a whole, they must be tightly regulated. To regulate metabolism, various mechanisms have evolved that affect metabolic tools, that is, the catalytic activity of enzymes.

Normal metabolism is characterized by adaptive changes during fasting, physical activity, pregnancy and lactation. Metabolic disorders occur, for example, due to malnutrition, lack of vitamins, deficiency of certain enzymes or hormone imbalance. Therefore, knowledge of the general patterns of normal metabolism is necessary for the future doctor to understand the causes of many diseases.

The occurrence and development of most pathological processes are based on biochemical changes. This mainly relates to changes in the metabolism of the main biological macromolecules: proteins, carbohydrates and lipids. Understanding metabolic processes includes knowledge of the structure and functions of macromolecules, as well as the characteristics of their digestion, absorption, transport and directly those chemical transformations that occur with these substances in a living organism. It is important to consider each metabolic process not isolated O, as an artificial scheme, but to take into account the peculiarities of its course in various tissues and organs, the possibilities of its regulation and, of course, its relationship with other metabolic pathways.

The purpose of studying the module “General patterns of metabolism. Metabolism of carbohydrates, lipids, proteins and its regulation" is: to be able to interpret the general patterns of metabolism, as well as the characteristics of the metabolism of carbohydrates, lipids and proteins in normal conditions and in pathology for the subsequent use of these data in the clinic of internal diseases.

General patterns of metabolism. Metabolism of carbohydrates, lipids, proteins and its regulation” includes the following content modules:

1. Protein metabolism and its regulation. Enzymopathies of amino acid metabolism

2. The role of enzymes and vitamins in metabolism

3. Lipid metabolism and its regulation

4. Metabolism and energy

5. Carbohydrate metabolism and its regulation

AMINO ACIDS. PEPTIDES. PROTEINS

Introduction

Amino acids are considered as derivatives of carboxylic acids, in which the position of the amino group relative to the carboxyl group is usually indicated by the letters: , which is equivalent to the numbers 2, 3, 4, etc., respectively. Letters of the Greek alphabet are not used in IUPAC substitutive nomenclature.

About 300 different amino acids have been found in natural objects, but the most important, constantly found in all peptides and proteins, are 20 α-amino acids ( see table 1). They are encoded by the genetic code, and they are usually called proteinogenic(sometimes canonical).

Structure. Classification and nomenclature. Steroisomerism

α-Amino acids are heterofunctional compounds whose molecules contain an amino group and a carboxyl group at the same carbon atom.

For normal growth of a child's body, a mandatory supply of two more amino acids is necessary, although in adults they are synthesized in sufficient quantities. These amino acids are called partially replaceable. The synthesis of tyrosine and cysteine ​​requires essential amino acids, which is why these two acids are called conditionally replaceable. Tyrosine is synthesized in the body by hydroxylation of phenylalanine, and methionine is required to produce cysteine.

α-Amino acids are necessary for the biosynthesis of not only peptides and proteins, but also phospholipids, nucleic bases, porphyrin compounds, as well as for performing such specific tasks as transfer of an amino group, methyl group, guanidine group, etc.

The main source of α-amino acids for humans and animals are food proteins. Depending on the content of essential amino acids, proteins are divided into full-fledged And inferior . For example, proteins from dairy, fish, meat products, some seafood (squid, crab meat), eggs, as well as some proteins of plant origin (soy, peas, beans) are complete, since they contain all the essential amino acids in the required proportions. In the main groups of food products, leucine and lysine predominate among the essential amino acids; their content ranges from 7.0 to 11% of the total content of α-amino acids ( see table). A relatively low content of tryptophan in products is typical (no more than 2%) and methionine (from 1.5 to 3.5%).

Table 2 Protein content of selected foods

Mixtures of α-amino acids are preparations for parenteral nutrition (bypassing the gastrointestinal tract) of patients with severe pathological complications.

Nomenclature

The names of α-amino acids can be constructed using substitutive nomenclature, but almost always only their trivial names accepted by the IUPAC nomenclature are used. Trivial names of α-amino acids are usually associated with sources of excretion. The simplest amino acid, first isolated from gelatin hydrolyzate and having a sweet taste, was called glycocol (from Greek..glykys- sweet and colla- glue, i.e. “sweet from glue”), later it received the name glycine.

In the names of aliphatic amino acids according to substitution nomenclature the amino group is indicated by the prefix amino, and the carboxyl group as a senior group is suffixed - new acid. The names of aromatic amino acids use benzoic acid.

Stereoisomerism

In all (except glycine, which is achiral) natural amino acids, the carbon atom is asymmetric, and most of these compounds (except isoleucine and threonine) have only one chiral center. Therefore, they exist in the form of two optical isomers (L- and D-enantiomers) Almost all natural amino acids are L-form, and D-amino acids, as a rule, are not absorbed by living organisms. Interestingly, most L-series amino acids taste sweet, while D-series amino acids taste bitter or tasteless.