Amino acids are called carboxylic acids containing an amino group and a carboxyl group. Natural amino acids are 2-aminocarboxylic acids, or α-amino acids, although there are such amino acids as β-alanine, taurine, γ-aminobutyric acid. The generalized formula for an α-amino acid looks like this:
α-amino acids at the 2 carbon atom have four different substituents, that is, all α-amino acids, except for glycine, have an asymmetric (chiral) carbon atom and exist in the form of two enantiomers - L- and D-amino acids. Natural amino acids belong to the L-series. D-amino acids are found in bacteria and peptide antibiotics.
All amino acids in aqueous solutions can exist as bipolar ions, and their total charge depends on the pH of the medium. The pH value at which the total charge is zero is called the isoelectric point. At the isoelectric point, the amino acid is a zwitterion, that is, its amine group is protonated, and the carboxyl group is dissociated. In the neutral pH region, most amino acids are zwitterions:
Amino acids do not absorb light in the visible region of the spectrum, aromatic amino acids absorb light in the UV region of the spectrum: tryptophan and tyrosine at 280 nm, phenylalanine at 260 nm.
Amino acids are characterized by some chemical reactions that are of great importance for laboratory practice: a colored ninhydrin test for the α-amino group, reactions characteristic of sulfhydryl, phenolic and other groups of amino acid radicals, acetylation and the formation of Schiff bases by amino groups, esterification by carboxyl groups.
The biological role of amino acids:
are structural elements of peptides and proteins, the so-called proteinogenic amino acids. The composition of proteins includes 20 amino acids that are encoded by the genetic code and are included in proteins during translation, some of them can be phosphorylated, acylated or hydroxylated;
can be structural elements of other natural compounds - coenzymes, bile acids, antibiotics;
are signaling molecules. Some of the amino acids are neurotransmitters or precursors of neurotransmitters, hormones and histohormones;
are essential metabolites, for example, some amino acids are precursors of plant alkaloids, or serve as nitrogen donors, or are vital components of nutrition.
The classification of proteinogenic amino acids is based on the structure and polarity of the side chains:
1. Aliphatic amino acids:
glycine, gly,G,Gly
alanine, ala, A,Ala
valine, shaft,V,Val*
leucine, lei,L,Leu*
isoleucine, ile, I,Ile*
These amino acids do not contain heteroatoms or cyclic groups in the side chain and are characterized by a pronounced low polarity.
cysteine, cis,C,Cys
methionine, meth,M,Met*
3. Aromatic amino acids:
phenylalanine, hair dryer,F,Phe*
tyrosine, shooting range,Y,Tyr
tryptophan, three,W,Trp*
histidine, gis,H,His
Aromatic amino acids contain mesomeric resonantly stabilized cycles. In this group, only the amino acid phenylalanine exhibits low polarity, tyrosine and tryptophan are characterized by noticeable polarity, and histidine even by high polarity. Histidine can also be classified as a basic amino acid.
4. Neutral amino acids:
serine, ser,S, Ser
threonine, tre,T,Thr*
asparagine, asn, N, Asn
glutamine, gln, Q,Gln
Neutral amino acids contain hydroxyl or carboxamide groups. Although the amide groups are non-ionic, the molecules of asparagine and glutamine are highly polar.
5. Acidic amino acids:
aspartic acid (aspartate), asp,D,Asp
glutamic acid (glutamate), deep, E,Glu
The carboxyl groups of the side chains of acidic amino acids are completely ionized over the entire range of physiological pH values.
6. Basic amino acids:
lysine, l from, K, Lys*
arginine, arg,R,Arg
The side chains of basic amino acids are completely protonated in the neutral pH region. A highly basic and very polar amino acid is arginine containing a guanidine moiety.
7. Imino acid:
proline, about,P,Pro
The side chain of proline consists of a five-membered ring, including an α-carbon atom and an α-amino group. Therefore, proline, strictly speaking, is not an amino acid, but an imino acid. The nitrogen atom in the ring is a weak base and does not protonate at physiological pH values. Due to the cyclic structure, proline causes bends in the polypeptide chain, which is very important for the structure of collagen.
Some of the listed amino acids cannot be synthesized in the human body and must be supplied with food. These essential amino acids are marked with asterisks.
As mentioned above, proteinogenic amino acids are the precursors of some valuable biologically active molecules.
Two biogenic amines β-alanine and cysteamine are part of coenzyme A (coenzymes are derivatives of water-soluble vitamins that form the active center of complex enzymes). β-Alanine is formed by the decarboxylation of aspartic acid, and cysteamine by the decarboxylation of cysteine:
β-alanine 
cysteamine
The glutamic acid residue is part of another coenzyme - tetrahydrofolic acid, a derivative of vitamin B c.
Other biologically valuable molecules are conjugates of bile acids with the amino acid glycine. These conjugates are stronger acids than basic acids, are formed in the liver and are present in bile as salts.
glycocholic acid
Proteinogenic amino acids are the precursors of some antibiotics - biologically active substances synthesized by microorganisms and inhibiting the reproduction of bacteria, viruses and cells. The most famous of them are penicillins and cephalosporins, which make up the group of β-lactam antibiotics and are produced by molds of the genus Penicillium. They are characterized by the presence in the structure of a reactive β-lactam ring, with the help of which they inhibit the synthesis of cell walls of gram-negative microorganisms.
general formula of penicillins
From amino acids by decarboxylation, biogenic amines are obtained - neurotransmitters, hormones and histohormones.
The amino acids glycine and glutamate are themselves neurotransmitters in the central nervous system.
dopamine (neurotransmitter) norepinephrine (neurotransmitter)
adrenaline (hormone) histamine (mediator and histohormone)
serotonin (neurotransmitter and histohormone) GABA (neurotransmitter)
thyroxine (hormone)
A derivative of the amino acid tryptophan is the best-known naturally occurring auxin, indoleacetic acid. Auxins are plant growth regulators, they stimulate the differentiation of growing tissues, the growth of cambium, roots, accelerate the growth of fruits and the fall of old leaves, their antagonists are abscisic acid.
indoleacetic acid
Derivatives of amino acids are also alkaloids - natural nitrogen-containing compounds of the main nature, formed in plants. These compounds are extremely active physiological compounds widely used in medicine. Examples of alkaloids are the phenylalanine derivative papaverine, the isoquinoline alkaloid of the hypnotic poppy (an antispasmodic), and the tryptophan derivative physostigmine, an indole alkaloid from Calabar beans (an anticholinesterase drug):
papaverine physostigmine
Amino acids are extremely popular objects of biotechnology. There are many options for the chemical synthesis of amino acids, but the result is racemates of amino acids. Since only L-isomers of amino acids are suitable for food industry and medicine, racemic mixtures must be separated into enantiomers, which presents a serious problem. Therefore, the biotechnological approach is more popular: enzymatic synthesis using immobilized enzymes and microbiological synthesis using whole microbial cells. In both latter cases, pure L-isomers are obtained.
Amino acids are used as food additives and feed components. Glutamic acid enhances the taste of meat, valine and leucine improve the taste of baked goods, glycine and cysteine are used as antioxidants in canning. D-tryptophan can be used as a sugar substitute as it is many times sweeter. Lysine is added to feed for farm animals, since most vegetable proteins contain a small amount of the essential amino acid lysine.
Amino acids are widely used in medical practice. These are amino acids such as methionine, histidine, glutamic and aspartic acids, glycine, cysteine, valine.
In the last decade, amino acids have been added to skin and hair care products.
Chemically modified amino acids are also widely used in industry as surfactants in the synthesis of polymers, in the production of detergents, emulsifiers, and fuel additives.
PROTEINS
Proteins are macromolecular substances consisting of amino acids linked by peptide bonds.
It is proteins that are the product of genetic information transmitted from generation to generation and carry out all life processes in the cell.
Protein Functions:
catalytic function. The most numerous group of proteins are enzymes - proteins with catalytic activity that speed up chemical reactions. Examples of enzymes are pepsin, alcohol dehydrogenase, glutamine synthetase.
Structural function. Structural proteins are responsible for maintaining the shape and stability of cells and tissues, these include keratins, collagen, fibroin.
transport function. Transport proteins carry molecules or ions from one organ to another or across membranes within a cell, such as hemoglobin, serum albumin, ion channels.
protective function. Proteins of the homeostasis system protect the body from pathogens, foreign information, blood loss - immunoglobulins, fibrinogen, thrombin.
regulatory function. Proteins carry out the functions of signaling substances - some hormones, histohormones and neurotransmitters, are receptors for signaling substances of any structure, provide further signal transmission in the biochemical signaling chains of the cell. Examples are the growth hormone somatotropin, the hormone insulin, H- and M-cholinergic receptors.
motor function. With the help of proteins, the processes of contraction and other biological movement are carried out. Examples are tubulin, actin, myosin.
spare function. Plants contain storage proteins, which are valuable nutrients; in animals, muscle proteins serve as reserve nutrients that are mobilized in case of emergency.
Proteins are characterized by the presence of several levels of structural organization.
primary structure A protein is the sequence of amino acid residues in a polypeptide chain. A peptide bond is a carboxamide bond between the α-carboxyl group of one amino acid and the α-amino group of another amino acid.
alanylphenylalanylcysteylproline
The peptide bond has several features:
a) it is resonantly stabilized and therefore is located practically in the same plane - it is planar; rotation around the C-N bond requires a lot of energy and is difficult;
b) the -CO-NH- bond has a special character, it is less than ordinary, but more than double, that is, there is a keto-enol tautomerism:
c) substituents in relation to the peptide bond are in trance-position;
d) the peptide backbone is surrounded by side chains of various nature, interacting with the surrounding solvent molecules, free carboxyl and amino groups are ionized, forming cationic and anionic centers of the protein molecule. Depending on their ratio, the protein molecule receives a total positive or negative charge, and is also characterized by one or another pH value of the medium when the isoelectric point of the protein is reached. Radicals form salt, ether, disulfide bridges inside the protein molecule, and also determine the range of reactions inherent in proteins.
At present, it has been agreed to consider polymers consisting of 100 or more amino acid residues as proteins, polymers consisting of 50-100 amino acid residues as polypeptides, and polymers consisting of less than 50 amino acid residues as low molecular weight peptides.
Some low molecular weight peptides play an independent biological role. Examples of some of these peptides:
Glutathione, γ-glu-cis-gly, is one of the most widespread intracellular peptides involved in redox processes in cells and the transport of amino acids across biological membranes.
Carnosine - β-ala-gis - a peptide contained in the muscles of animals, eliminates the products of lipid peroxidation, accelerates the breakdown of carbohydrates in the muscles and is involved in energy metabolism in the muscles in the form of phosphate.
Vasopressin is a hormone of the posterior pituitary gland involved in the regulation of water metabolism in the body:
Phalloidin is a poisonous fly agaric polypeptide, in negligible concentrations causes the death of the body due to the release of enzymes and potassium ions from cells:
Gramicidin is an antibiotic that acts on many gram-positive bacteria, changes the permeability of biological membranes for low molecular weight compounds and causes cell death:
Met-enkephalin - thyr-gli-gli-fen-met - a peptide synthesized in neurons and relieves pain.
Secondary structure of a protein is a spatial structure formed as a result of interactions between the functional groups of the peptide backbone.
The peptide chain contains many CO and NH groups of peptide bonds, each of which is potentially capable of participating in the formation of hydrogen bonds. There are two main types of structures that allow this to happen: the α-helix, in which the chain coils like a telephone cord, and the β-pleated structure, in which elongated sections of one or more chains are stacked side by side. Both of these structures are very stable.
The α-helix is characterized by extremely dense packing of the twisted polypeptide chain, each turn of the right-handed helix has 3.6 amino acid residues, the radicals of which are always directed outward and slightly backward, that is, to the beginning of the polypeptide chain.
The main characteristics of the α-helix:
The α-helix is stabilized by hydrogen bonds between the hydrogen atom at the nitrogen of the peptide group and the carbonyl oxygen of the residue, four positions away from the given one along the chain;
all peptide groups participate in the formation of a hydrogen bond, this ensures maximum stability of the α-helix;
all nitrogen and oxygen atoms of the peptide groups are involved in the formation of hydrogen bonds, which significantly reduces the hydrophilicity of the α-helical regions and increases their hydrophobicity;
α-helix is formed spontaneously and is the most stable conformation of the polypeptide chain, corresponding to a minimum of free energy;
in a polypeptide chain of L-amino acids, the right helix, usually found in proteins, is much more stable than the left one.
The possibility of forming an α-helix is due to the primary structure of the protein. Some amino acids prevent the peptide backbone from twisting. For example, adjacent carboxyl groups of glutamate and aspartate mutually repel each other, which prevents the formation of hydrogen bonds in the α-helix. For the same reason, the chain coiling is difficult in places of positively charged lysine and arginine residues located close to each other. However, proline plays the greatest role in breaking the α-helix. Firstly, in proline, the nitrogen atom is part of a rigid ring, which prevents rotation around the N-C bond, and secondly, proline does not form a hydrogen bond due to the absence of hydrogen at the nitrogen atom.
β-folding is a layered structure formed by hydrogen bonds between linearly arranged peptide fragments. Both chains may be independent or belong to the same polypeptide molecule. If the chains are oriented in the same direction, then such a β-structure is called parallel. In the case of the opposite direction of the chains, that is, when the N-terminus of one chain coincides with the C-terminus of the other chain, the β-structure is called antiparallel. Energetically, antiparallel β-folding with almost linear hydrogen bridges is more preferable.
parallel β-folding antiparallel β-folding
Unlike the α-helix, which is saturated with hydrogen bonds, each section of the β-folding chain is open to the formation of additional hydrogen bonds. The amino acid side radicals are oriented almost perpendicular to the leaf plane, alternately up and down.
In those areas where the peptide chain bends rather steeply, there is often a β-loop. This is a short fragment in which 4 amino acid residues are bent 180 o and stabilized by one hydrogen bridge between the first and fourth residues. Large amino acid radicals interfere with the formation of the β-loop, so it most often includes the smallest amino acid, glycine.
Suprasecondary protein structure is some specific order of alternation of secondary structures. A domain is understood as a separate part of a protein molecule, which has a certain degree of structural and functional autonomy. Now domains are considered to be fundamental elements of the structure of protein molecules, and the ratio and nature of the layout of α-helices and β-layers provides more for understanding the evolution of protein molecules and phylogenetic relationships than a comparison of primary structures. The main task of evolution is the construction of new proteins. There is an infinitesimal chance of synthesizing such an amino acid sequence by chance that would satisfy the packaging conditions and ensure the fulfillment of functional tasks. Therefore, there are often proteins with different functions, but similar in structure to such an extent that it seems that they had a common ancestor or evolved from each other. It seems that evolution, faced with the need to solve a certain problem, prefers not to design proteins for this first, but to adapt already well-established structures for this, adapting them for new purposes.
Some examples of frequently repeated supra-secondary structures:
αα' - proteins containing only α-helices (myoglobin, hemoglobin);
ββ' – proteins containing only β-structures (immunoglobulins, superoxide dismutase);
βαβ' is the structure of the β-barrel, each β-layer is located inside the barrel and is associated with an α-helix located on the surface of the molecule (triose phosphoisomerase, lactate dehydrogenase);
"zinc finger" - a protein fragment consisting of 20 amino acid residues, the zinc atom is associated with two cysteine and two histidine residues, resulting in a "finger" of about 12 amino acid residues, can bind to the regulatory regions of the DNA molecule;
"leucine zipper" - interacting proteins have an α-helical region containing at least 4 leucine residues, they are located 6 amino acids apart from each other, that is, they are located on the surface of every second turn and can form hydrophobic bonds with leucine residues of another protein . With the help of leucine zippers, for example, molecules of strongly basic histone proteins can be combined into complexes, overcoming a positive charge.
Tertiary structure of a protein- this is the spatial arrangement of the protein molecule, stabilized by bonds between the side radicals of amino acids.
Types of bonds that stabilize the tertiary structure of a protein:
electrostatic hydrogen hydrophobic disulfide
interaction communication interaction communication
Depending on the folding of the tertiary structure, proteins can be classified into two main types - fibrillar and globular.
Fibrillar proteins are water-insoluble long filamentous molecules, the polypeptide chains of which are extended along one axis. These are mainly structural and contractile proteins. A few examples of the most common fibrillar proteins are:
α-Keratins. Synthesized by epidermal cells. They account for almost all the dry weight of hair, wool, feathers, horns, nails, claws, needles, scales, hooves, and tortoise shell, as well as a significant part of the weight of the outer layer of the skin. This is a whole family of proteins, they are similar in amino acid composition, contain many cysteine residues and have the same spatial arrangement of polypeptide chains. In hair cells, keratin polypeptide chains are first organized into fibers, from which structures are then formed like a rope or a twisted cable, which eventually fills the entire space of the cell. At the same time, the hair cells become flattened and finally die, and the cell walls form a tubular sheath around each hair, called the cuticle. In α-keratin, the polypeptide chains are in the form of an α-helix, twisted one around the other into a three-core cable with the formation of cross disulfide bonds. N-terminal residues are located on the same side (parallel). Keratins are insoluble in water due to the predominance of amino acids with non-polar side radicals in their composition, which are turned towards the aqueous phase. During perm, the following processes occur: first, disulfide bridges are destroyed by reduction with thiols, and then, when the hair is given the necessary shape, it is dried by heating, while due to oxidation with air oxygen, new disulfide bridges are formed that retain the shape of the hairstyle.
β-Keratins. These include silk and cobweb fibroin. They are antiparallel β-folded layers with a predominance of glycine, alanine and serine in the composition.
Collagen. The most common protein in higher animals and the main fibrillar protein of connective tissues. Collagen is synthesized in fibroblasts and chondrocytes - specialized connective tissue cells, from which it is then pushed out. Collagen fibers are found in the skin, tendons, cartilage and bones. They do not stretch, surpass steel wire in strength, collagen fibrils are characterized by transverse striation. When boiled in water, fibrous, insoluble and indigestible collagen is converted to gelatin by hydrolysis of some of the covalent bonds. Collagen contains 35% glycine, 11% alanine, 21% proline and 4-hydroxyproline (an amino acid found only in collagen and elastin). This composition determines the relatively low nutritional value of gelatin as a food protein. Collagen fibrils are made up of repeating polypeptide subunits called tropocollagen. These subunits are arranged along the fibril in parallel head-to-tail bundles. The shift of the heads gives the characteristic transverse striation. Voids in this structure, if necessary, can serve as a site for the deposition of crystals of hydroxyapatite Ca 5 (OH)(PO 4) 3 , which plays an important role in bone mineralization.
Tropocollagen subunits are composed of three polypeptide chains tightly twisted into a three-stranded rope, different from α- and β-keratins. In some collagens, all three chains have the same amino acid sequence, while in others only two chains are identical, and the third one differs from them. The tropocollagen polypeptide chain forms a left-handed helix, with only three amino acid residues per turn due to chain bends caused by proline and hydroxyproline. Three chains are interconnected, in addition to hydrogen bonds, by a covalent-type bond formed between two lysine residues located in adjacent chains:
As we get older, more and more cross-links are formed in and between the tropocollagen subunits, which makes the collagen fibrils stiffer and more brittle, and this changes the mechanical properties of cartilage and tendons, makes bones more brittle, and reduces the transparency of the cornea of the eye.
Elastin. Contained in the yellow elastic tissue of the ligaments and the elastic layer of connective tissue in the walls of large arteries. The main subunit of elastin fibrils is tropoelastin. Elastin is rich in glycine and alanine, contains a lot of lysine and little proline. The helical sections of elastin stretch when stretched, but return to their original length when the load is removed. The lysine residues of the four different chains form covalent bonds with each other and allow elastin to reversibly stretch in all directions.
Globular proteins are proteins whose polypeptide chain is folded into a compact globule, capable of performing a wide variety of functions.
The tertiary structure of globular proteins is most conveniently considered using the example of myoglobin. Myoglobin is a relatively small oxygen-binding protein found in muscle cells. It stores bound oxygen and promotes its transfer to the mitochondria. The myoglobin molecule contains one polypeptide chain and one hemogroup (heme) - a complex of protoporphyrin with iron. The main properties of myoglobin:
a) the myoglobin molecule is so compact that only 4 water molecules can fit inside it;
b) all polar amino acid residues, with the exception of two, are located on the outer surface of the molecule, and all of them are in a hydrated state;
c) most of the hydrophobic amino acid residues are located inside the myoglobin molecule and, thus, are protected from contact with water;
d) each of the four proline residues in the myoglobin molecule is located at the bend of the polypeptide chain, serine, threonine and asparagine residues are located at other places of the bend, since such amino acids prevent the formation of an α-helix if they are with each other;
e) a flat hemogroup lies in a cavity (pocket) near the surface of the molecule, the iron atom has two coordination bonds directed perpendicular to the heme plane, one of them is connected to the histidine residue 93, and the other serves to bind the oxygen molecule.
Starting from the tertiary structure, the protein becomes capable of performing its biological functions. The functioning of proteins is based on the fact that when the tertiary structure is laid on the surface of the protein, sites are formed that can attach other molecules, called ligands, to themselves. The high specificity of the interaction of the protein with the ligand is provided by the complementarity of the structure of the active center with the structure of the ligand. Complementarity is the spatial and chemical correspondence of interacting surfaces. For most proteins, tertiary structure is the maximum level of folding.
Quaternary protein structure- characteristic of proteins consisting of two or more polypeptide chains interconnected exclusively by non-covalent bonds, mainly electrostatic and hydrogen. Most often proteins contain two or four subunits, more than four subunits usually contain regulatory proteins.
Proteins having a quaternary structure are often called oligomeric. Distinguish between homomeric and heteromeric proteins. Homeric proteins are proteins in which all subunits have the same structure, for example, the catalase enzyme consists of four absolutely identical subunits. Heteromeric proteins have different subunits, for example, the RNA polymerase enzyme consists of five subunits of different structure that perform different functions.
The interaction of one subunit with a specific ligand causes conformational changes in the entire oligomeric protein and changes the affinity of other subunits for ligands; this property underlies the ability of oligomeric proteins to allosteric regulation.
The quaternary structure of a protein can be considered using the example of hemoglobin. It contains four polypeptide chains and four heme prosthetic groups, in which the iron atoms are in the ferrous form Fe 2+ . The protein part of the molecule - globin - consists of two α-chains and two β-chains, containing up to 70% α-helices. Each of the four chains has a characteristic tertiary structure, and one hemogroup is associated with each chain. The hemes of different chains are relatively far apart and have different angles of inclination. Few direct contacts are formed between two α-chains and two β-chains, while numerous contacts of the α 1 β 1 and α 2 β 2 type formed by hydrophobic radicals form between the α- and β-chains. A channel remains between α 1 β 1 and α 2 β 2.
Unlike myoglobin, hemoglobin is characterized by a significantly lower affinity for oxygen, which allows it, at low partial pressures of oxygen existing in tissues, to give them a significant part of the bound oxygen. Oxygen is more easily bound by hemoglobin iron at higher pH values and low CO 2 concentrations, characteristic of the lung alveoli; the release of oxygen from hemoglobin is favored by lower pH values and high concentrations of CO 2 inherent in tissues.
In addition to oxygen, hemoglobin carries hydrogen ions, which bind to histidine residues in the chains. Hemoglobin also carries carbon dioxide, which attaches to the terminal amino group of each of the four polypeptide chains, resulting in the formation of carbaminohemoglobin:
In erythrocytes, the substance 2,3-diphosphoglycerate (DFG) is present in sufficiently high concentrations, its content increases with ascent to high altitude and during hypoxia, facilitating the release of oxygen from hemoglobin in tissues. DFG is located in the channel between α 1 β 1 and α 2 β 2 interacting with positively infected groups of β-chains. When oxygen is bound by hemoglobin, DPG is displaced from the cavity. The erythrocytes of some birds do not contain DPG, but inositol hexaphosphate, which further reduces the affinity of hemoglobin for oxygen.
2,3-diphosphoglycerate (DPG)
HbA - normal adult hemoglobin, HbF - fetal hemoglobin, has a greater affinity for O 2, HbS - hemoglobin in sickle cell anemia. Sickle cell anemia is a serious hereditary disease associated with a genetic abnormality of hemoglobin. In the blood of sick people, there is an unusually large number of thin sickle-shaped red blood cells, which, firstly, are easily torn, and secondly, clog the blood capillaries. At the molecular level, hemoglobin S differs from hemoglobin A in one amino acid residue in position 6 of the β-chains, where valine is located instead of a glutamic acid residue. Thus, hemoglobin S contains two negative charges less, the appearance of valine leads to the appearance of a “sticky” hydrophobic contact on the surface of the molecule, as a result, during deoxygenation, deoxyhemoglobin S molecules stick together and form insoluble abnormally long filamentous aggregates, leading to deformation of erythrocytes.
There is no reason to think that there is an independent genetic control over the formation of levels of protein structural organization above the primary one, since the primary structure determines both secondary, tertiary, and quaternary (if any). The native conformation of a protein is the most thermodynamically stable structure under the given conditions.
Lecture #3Topic: "Amino acids - structure, classification, properties, biological role"
Amino acids - nitrogen-containing organic compounds, the molecules of which contain the amino group -NH2 and the carboxyl group -COOH
The simplest representative is aminoethanoic acid H2N - CH2 - COOH
Amino acid classification
There are 3 main classifications of amino acids:
Physico-chemical – based on differences in the physicochemical properties of amino acids
Hydrophobic amino acids (non-polar). The components of the radicals usually contain hydrocarbon groups, where the electron density is evenly distributed and there are no charges and poles. Electronegative elements may also be present in their composition, 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 - they acquire a positive charge in a neutral environment.
Irreplaceable amino acids, they are also called "essential". They cannot be synthesized in the human body and must be obtained from food. Their 8 and 2 more amino acids are partially essential.
Partially irreplaceable: arginine, histidine.
Interchangeable(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 structural features.
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:
With congenital disorders associated with the absorption of amino acids. In this case, some protein substances can cause allergic reactions of the body, including the appearance of problems in the gastrointestinal tract, itching and nausea.
Amino acid digestibility
The speed and completeness of assimilation of amino acids depends on the type of products containing them. The amino acids contained in the protein of eggs, 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.
Useful 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, with cirrhosis and fatty degeneration of the liver.
For certain neuropsychiatric diseases, glutamine, aminobutyric acids are used. Glutamic acid is also used in cooking as a flavoring agent. 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 the normal growth of the body, participates in the processes of blood formation.
The main sources of lysine and methionine are cottage cheese, beef, some types of fish (cod, pike perch, herring). Tryptophan is found in optimal amounts in by-products, veal and game.heart attack.
Amino acids for health, energy and beauty
For successful muscle building 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 nutritional 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.
Modern protein nutrition is impossible to imagine without considering the role of individual amino acids. Even with an overall positive protein balance, the animal's body may experience a lack of protein. This is due to the fact that the assimilation of individual amino acids is interconnected in each other, a lack or excess of one amino acid can lead to a lack of another.
Some amino acids are not synthesized in the human body and animals. They are called indispensable. There are only ten such amino acids. Four of them are critical (limiting) - they most often limit the growth and development of animals.
Methionine and cystine are the main limiting amino acids in poultry diets, and lysine in pig diets. The organism must receive a sufficient amount of the main limiting acid in the diet so that other amino acids can be effectively used for protein synthesis.
This principle is illustrated by the Liebig barrel, where the fill level of the barrel represents the level of protein synthesis in the animal's body. The shortest board in the barrel "limits" the ability to hold liquid in it. If this board is extended, then the volume of liquid held in the barrel will increase to the level of the second limiting board.
The most important factor determining the productivity of animals is the balance of amino acids contained in it in accordance with physiological needs. Numerous studies have shown that in pigs, depending on the breed and sex, the need for amino acids differs quantitatively. But the ratio of essential amino acids for the synthesis of 1 g of protein is the same. This ratio of essential amino acids to lysine, as the main limiting amino acid, is called the "ideal protein" or "ideal amino acid profile". (
Lysine
is part of almost all proteins of animal, plant and microbial origin, however, proteins of cereal crops are poor in lysine.
- Lysine regulates the reproductive function, with a lack of it, the formation of sperm and eggs is disrupted.
- Necessary for the growth of young animals, the formation of tissue proteins. Lysine takes part in the synthesis of nucleoproteins, chromoproteins (hemoglobin), thereby regulating the pigmentation of animal hair. Regulates the amount of protein breakdown products in tissues and organs.
- Promotes calcium absorption
- Participates in the functional activity of the nervous and endocrine systems, regulates the metabolism of proteins and carbohydrates, however, reacting with carbohydrates, lysine becomes inaccessible to absorption.
- Lysine is the initial substance in the formation of carnitine, which plays an important role in fat metabolism.
Methionine and cystine sulfur-containing amino acids. At the same time, methionine can be transformed into cystine, so these amino acids are normalized together, and in case of a deficiency, methionine supplements are introduced into the diet. Both of these amino acids are involved in the formation of derivatives of the skin - hair, feather; Together with vitamin E, they regulate the removal of excess fat from the liver, and are necessary for the growth and reproduction of cells, red blood cells. With a lack of methionine, cystine is inactive. However, a significant excess of methionine in the diet should not be allowed.
Methionine
promotes the deposition of fat in the muscles, is necessary for the formation of new organic compounds of choline (vitamin B4), creatine, adrenaline, niacin (vitamin B5), etc.
Methionine deficiency in diets leads to a decrease in the level of plasma proteins (albumin), causes anemia (a decrease in the level of hemoglobin in the blood), while a lack of vitamin E and selenium contributes to the development of muscular dystrophy. An insufficient amount of methionine in the diet causes stunting of young animals, loss of appetite, decreased productivity, increased feed costs, fatty liver, impaired kidney function, anemia and malnutrition.
An excess of methionine impairs the use of nitrogen, causes degenerative changes in the liver, kidneys, pancreas, increases the need for arginine, glycine. With a large excess of methionine, an imbalance is observed (the balance of amino acids is disturbed, which is based on sharp deviations from the optimal ratio of essential amino acids in the diet), which is accompanied by metabolic disorders and inhibition of the growth rate in young animals.
Cystine is a sulfur-containing amino acid, interchangeable with methionine, participates in redox processes, metabolism of proteins, carbohydrates and bile acids, promotes the formation of substances that neutralize intestinal poisons, activates insulin, together with tryptophan, cystine participates in the synthesis in the liver of bile acids necessary for absorption products of digestion of fats from the intestines, is used for the synthesis of glutathione. Cystine has the ability to absorb ultraviolet rays. With a lack of cystine, cirrhosis of the liver, a delay in feathering and feather growth in young animals, fragility and loss (plucking) of feathers in an adult bird, and a decrease in resistance to infectious diseases are noted.
tryptophan
determines the physiological activity of digestive tract enzymes, oxidative enzymes in cells and a number of hormones, participates in the renewal of blood plasma proteins, determines the normal functioning of the endocrine and hematopoietic apparatuses, the reproductive system, the synthesis of gamma globulins, hemoglobin, nicotinic acid, ocular purpura, etc. in the diet of tryptophan, the growth of young animals slows down, egg production of laying hens decreases, feed costs for products increase, endocrine and sex glands atrophy, blindness occurs, anemia develops (the number of red blood cells and hemoglobin levels in the blood decrease), resistance and immune properties of the body decrease, fertilization and hatchability of eggs . In pigs fed a diet poor in tryptophan, feed intake is reduced, perverted appetite, roughening of the bristles and emaciation appear, fatty liver is noted. Deficiency of this amino acid also leads to sterility, irritability, convulsions, cataract formation, negative nitrogen balance and weight loss. Tryptophan, being a precursor (provitamin) of nicotinic acid, prevents the development of pellagra.
CHAPTER 2. 2.1. PROTEINS
1. Neutral amino acid is:
1) arginine 4) aspartic acid
2) lysine 5) histidine
2. The bipolar ion of a monoaminomonocarboxylic amino acid is charged:
1) negative
2) electrically neutral
3) positive
Reduced amino acid
H 2 N-CH 2 -(CH 2) 3 -CHNH 2 -COOH
belongs to the group of amino acids:
1) hydrophobic
2) polar but uncharged
3) positively charged
4) negatively charged
4.Set match:
amino acid radicals amino acids
a) histidine
a) histidine
c) phenylalanine
e) tryptophan
5. An imino acid is:
1) glycine 4) serine
2) cysteine 5) proline
3) arginine
6. Amino acids that make up proteins are:
1) α-amino derivatives of carboxylic acids
2) β-amino derivatives of carboxylic acids
3) α-amino derivatives of unsaturated carboxylic acids
7. Name the amino acid:
1. Name the amino acid:
9.Set match:
Amino Acid Group
4. citrulline monoamino monocarboxylic
5. cystine diaminomonocarboxylic
6. threonine monoaminodicarboxylic
7. glutamic diaminodicarboxylic
10. Sulfur-containing amino acid is:
8. Threonine 4) tryptophan
9. Tyrosine 5) methionine
10. Cysteine
11. Proteins do not include amino acids:
1) glutamine 3) arginine
2) γ-aminobutyric 4) β-alanine
acid 4) threonine
12. Hydroxy group contains amino acids:
1) alanine 4) methionine
2) serine 5) threonine
3) cysteine
13. Set match:
elemental chemical content
protein composition in percent
1) carbon a) 21-23
2) oxygen b) 0-3
3) nitrogen c) 6-7
4) hydrogen 5) 50-55
5) sulfur e) 15-17
14. The bond does not participate in the formation of the tertiary structure of the protein:
1) hydrogen
2) peptide
3) disulfide
4) hydrophobic interaction
15. The molecular weight of a protein varies within:
1) 0.5-1.0 2) 1.0-5 3) 6-10 thousand kDa
16. During protein denaturation, the following does not occur:
1) violations of the tertiary structure
3) violations of the secondary structure
2) hydrolysis of peptide bonds
4) dissociation of subunits
Spectrophotometric method of quantitative
The definition of protein is based on their ability to absorb light in the UV region at:
1) 280 nm 2) 190 nm 3) 210 nm
The amino acids arginine and lysine are
20-30% amino acid composition of proteins:
1) albumin 4) histones
2) prolamins 5) proteinoids
3) globulins
19. Keratin hair proteins belong to the group:
1) prolamins 4) glutelins
2) protamines 5) globulins
3) proteinoids
20. 50% of blood plasma proteins are:
1) α-globulins 4) albumin
2) β-globulins 5) prealbumin
3) γ-globulins
21. In the nuclei of eukaryotic cells there are mainly:
1) protamines 3) albumins
2) histones 4) globulins
22. Proteinoids include:
1) zein - corn seed protein 4) fibroin - silk protein
2) albumin - egg protein 5) collagen - protein compound
3) hordein - protein of barley seed tissue
Leonid Ostapenko
Hormonal connectionsIt turned out that branched-chain amino acids can not only prevent central fatigue and muscle breakdown, but can also leave behind the adverse hormonal fluctuations caused by intense exercise.
For example, leucine alone is able to stimulate the release and/or activation of growth hormone, somatomedins and insulin. This has a direct anabolic and anti-catabolic effect on the muscle.
In experiments conducted during 1992 (European Journal of Applied Physiology, 64: 272), researchers provided test athletes with a commercial dietary product containing 5.14 grams of leucine, 2.57 grams of isoleucine, and 2.57 grams of valine (2:2 ratio). 1:1). In addition to BCAAs, 12 grams of milk proteins, 20 grams of fructose, 8.8 grams of other carbohydrates, and 1.08 grams of fat were included in this product.
The scientists' goal was to determine if BCAA supplementation could affect the hormonal response found by their subjects (male marathon runners) when running at a constant speed. To keep the results "clean", the athletes fasted for 12 hours before testing and took their BCAA blends 90 minutes before the test run.
Test results showed that some subjects experienced a significant rise in BCAAs in their blood within hours of consuming the mixture. The researchers concluded that BCAAs can certainly have an anti-catabolic effect because the ratio of testosterone to cortisol - the main indicator of anabolic status - has been improved. You know that cortisol is the most powerful catabolic hormone, the increased level of which in the body literally "devours" your hard-earned muscles.
In another study (European Journal of Applied Physiology, 65: 394, 1992), researchers gave sixteen climbers a total of 11.52 grams of BCAAs—5.76 grams of leucine, 2.88 grams of isoleucine, and 2.88 grams of valine each day. The results of the experiment brilliantly confirmed that supplementing the diet with BCAAs helped prevent muscle loss as these 16 people made the grueling trek through the Peruvian Andes.
Honestly, in a good way you will envy all these sneakers, marathon runners and climbers - all scientists are engaged in them, and only an unfortunate bodybuilder is forced, at his own peril and risk, to drive into himself completely unthinkable combinations of everything that would bring his cherished goal closer even for a moment - become strong and big! But it seems that we were distracted by emotions, and this cannot be done during a serious conversation ... Let's return to our topic.
So, BCAAs have been found to have anti-catabolic effects and therefore can be considered a key factor in increasing anabolic stimulation. There is some scientific evidence for this.
One of the serious experiments carried out by the American scientist Ferrando and his colleagues at NASA in Houston, USA, was covered in the Journal of Parenteral and Enteral Nutrition (JPEN). Keep in mind that JPEN, the premier journal accepted without reservation by orthodox nutritionists, contains numerous articles on nutritional therapy, especially with regard to amino acids.
This trial compared the effect of 11 g of BCAAs with that of 11 g of the three essential amino acids (threonine, histidine, and methionine) on protein synthesis and breakdown in 4 healthy men. Each daily dose of the drink with these BCAAs also included 50 g of carbohydrates.
This resulted in three important observations:
First- Dietary supplementation with any mixture of amino acids significantly increased (three to four times) blood levels of the corresponding amino acid.
Second- BCAA supplementation (but not another amino acid formula) significantly increased intracellular BCAA concentrations in muscle.
Third(but with the highest value) - amino acid supplementation significantly inhibited whole body protein breakdown (proteolysis) - with BCAAs providing more protection than "essential" amino acid formulas.
In my opinion, for the results of this experience, we could well rejoice along with many other people interested in such protection of their muscles.
A spoon of tar
You can't have everything going great all the time. That doesn't happen in life. This does not happen in the world of biochemistry, especially when it comes to experiments.
As we already know, nervous relaxation translates into premature fatigue during exercise, and one of the recommended remedies for this condition is to take branched chain amino acids, or BCAAs, before training. As mentioned above, tryptophan competes with other amino acids for entry into the brain, and is usually outmatched by large neutral amino acids such as BCAAs. Past research has shown that pre-workout BCAA supplementation delays the combined effects of carbohydrates, insulin, and tryptophan, thus delaying unwanted central nervous system fatigue.
However, a recent study, fortunately so far in rats, appeared to contradict this recommendation. The group of rats that took BCAAs showed a significant level of fatigue during exercise, and the scientists concluded that BCAAs cause a greater release of insulin than glucose, and this leads to premature fatigue through two mechanisms: 1) removal of glucose from the blood by insulin; And 2) reducing the rate of breakdown and release of stored hepatic glycogen, which is needed to maintain the correct level of blood glucose.
For now, the only theoretical lesson to be learned from this experience is that the combination of high carbs and high BCAAs before exercise can cause premature fatigue during exercise, especially when exertion lasts more than two hours. After training, of course, this situation develops in reverse. That's when you need a massive boost of insulin to promote muscle protein synthesis. In fact, if you are taking a supplement like one of the metabolic optimizers rich in both carbs and BCAAs, you would need to take it after your workout if you want to keep your energy levels high during your workout. Fortunately, these are only assumptions, and they need to be tested, but so far all elite athletes who take branched chain amino acids both before and after training have noted positive changes in both energy and muscle mass preservation.
How and when to take BCAAs
Standard recommendations for when to take BCAAs are the periods immediately before and after a training session. Within half an hour before training, it is very useful to take a couple of capsules of these amino acids. They will insure you, in case you do not have enough glycogen in your muscles and liver, so that you do not have to pay the price by breaking down the valuable amino acids that make up your muscle cells.
Naturally, after training, when the level of amino acids and glucose in the blood reaches very low levels, they must be immediately replenished, because only by restoring the energy potential of the cell, you can count on it to begin to unfold plastic processes, that is, regeneration and superregeneration of contractile elements.
The most favorable period for such reimbursement is the first half hour after class. Immediately after class, take a couple more BCAA capsules so that the increased rate of metabolic processes that continues by inertia does not “gobble up” valuable amino acids that build muscle cells in order to eliminate the energy hole.
Lee Haney, one of the "long-livers" on the throne of Mr. Olympia, for example, took a mixture of valine, leucine and isoleucine in a ratio of 2:2:1 after hard training, and in absolute terms this was expressed in 5 grams of valine and leucine, and 2.5 grams of isoleucine, and after aerobic training this dosage was reduced by half .
Some experts suggest that the ideal time to take BCAA supplements is immediately after a meal, which helps you keep your insulin levels high, and immediately after every workout, which speeds up the delivery of BCAAs to your hungry muscles when they are in a depleted state. They should, however, be taken with some form of complex carbohydrates at the same time, but not with simple sugars, which are ineffective at restoring muscle glycogen. In any case, you should never take BCAAs on an empty stomach - almost all researchers and practitioners are unanimous on this.
There are some more tricks, without knowing which even the most powerful BCAA dosages will not "play" into your favor. Please keep in mind that the main factor in the absorption of any amino acids is increased blood sugar and insulin. Without a doubt, insulin is the main anabolic hormone in the body. The question is, what is the best way to combine high levels of insulin with BCAAs?
Above all, ensure that important cofactors are present in your diet and supplementation plan. One of the most important of these cofactors is chromium, and the most desirable form of this trace element is chromium picolinate. Chromium increases the effectiveness of insulin, and because insulin transports amino acids to your muscles, you will get less than ideal results when taking BCAAs while deficient in chromium.
Other important cofactors include zinc, which is an insulin regulator, vitamins B6 and B12, which are important for protein metabolism, and biotin. A significant proportion of these cofactors will come from a good clean diet. Even so, it's also a good idea to take a good multivitamin and multimineral formula as a safety net in case you're not getting enough.
Of course, in order for BCAAs to work effectively, you should focus on their complex supplements, which include all three of these amino acids. They must all be present at the same time in order to maximize their uptake by the muscular system.
How much to accept and from which firms
The last question, but the most important and most difficult. Nobody knows how much to take; none of the scientific experiments, with the results of which we got acquainted, could not only categorically, but even in a recommendatory plan, name either the ratio between the individual BCAAs in their complex, or the daily or single dosages. Each of the champions involved in the advertising of this or that amino acid supplement claims that exactly what he took is the best. It seems to me that this is quite natural. After all, the individual characteristics of digestion and assimilation are so specific for each person that one of you will be best helped by the amino acid formula of the company twinlab, while the other will be delighted with the firm Weider, and the third one will foam at the mouth to prove that there is nothing better than the company's amino acids Multipower. The funny thing is that they will all be right, because this or that particular amino acid formula perfectly “fits” into the features of his body!
Therefore, experiment, friends, the future is yours, and tell us which drugs of which companies seemed to you the most effective, in what dosage, at what time of the day, and so on. The more we are able to collect such materials, the more accurately we will be able to determine the optimal doses and regimens for bodybuilders.
Good luck in your research activities!
