Amino acids that make up proteins structure nomenclature. Classification of proteinogenic amino acids. Amino acid composition of proteins
Subject and tasks of biological chemistry. Biochemistry as a molecular level
study of the structural organization, anabolism and catabolism of living matter.
The value of biochemistry in the training of a doctor.
biological chemistry (biochemistry) is a science that studies the chemical composition of living organisms, the transformation of substances and energy underlying their life activity. The totality of these transformations constitutes the biological metabolism, which is the basis of that form of motion of matter which we call life.
Living organisms have unusual properties that are absent in the accumulation of non-living molecules. These include the following properties: 1.1 Complexity and a high degree of organization. Living organisms are represented by millions of different species. 1.2 Any component of the body has a special purpose and a strictly defined function is performed. This applies even to individual chemical compounds (lipids, proteins, etc.). 1.3 The ability to extract, transform and use the energy of their environment - either in the form of organic nutrients or in the form of energy from solar radiation Metabolism is made up of many individual chemical reactions that occur in a living organism and are closely related to each other. The data of experimental biochemistry indicate the relationship and continuity of the process of absorption and assimilation of nutrients - assimilation and the process of their decomposition and isolation - dissimilation. The conjugation and interconnection of individual reactions that occur during the assimilation and dissimilation of nutrients in the body is also manifested in the conjugation of energy transformations that occur throughout the life of the organism.
1.4 Ability to accurately reproduce itself. The goal of biochemistry is to understand how the interactions of biomolecules with each other give rise to the features of the living state described above.
Biochemistry is divided into: 3.1 Static, studying the chemical composition of living matter; 3.2 Dynamic, studying the processes of metabolism in the body; 3.3 Functional, studying the processes underlying certain manifestations of vital activity. The first part is usually called organic chemistry and is presented in a special course, the second and third parts are actually biochemistry.
Biological chemistry studies the molecular processes that underlie the development and functioning of organisms. Biochemistry uses the methods of the "molecular" sciences - chemistry, physical chemistry, molecular physics, and in this respect biochemistry itself is a molecular science.
However, the main final tasks of biochemistry lie in the field of biology: it studies the laws of the biological, and not the chemical form of the motion of matter. On the other hand, the "molecular inventions" of nature, discovered by biochemists, find application in non-biological branches of knowledge and in industry (molecular bionics, biotechnology). In such cases, biochemistry acts as a method, and the subject of research and development are problems that go beyond biology. The place of biochemistry as a molecular level of biological research. The levels of research are a reflection of the levels of structural organization of biological systems that form a hierarchical series from the simplest systems (molecules of organisms, molecular level) to the extremely complex terrestrial biological system (biospheric level). The actual connections between branches of biology are far more complex than such simple diagrams would suggest. In particular, each simpler level of organization of living systems (and, accordingly, the level of their study) is a part of more complex levels. The very first level, the molecular level, is unique in that it is an integral part of the systems of all other levels of biology. Accordingly, such sections of biochemistry are distinguished, such as, for example, molecular genetics, biochemical ecology. The highest level - biospheric - includes all other levels.
The value of biochemical research.
From the definition of biological chemistry it follows that this is the chemistry of living beings. A living system differs from a non-living one in the exchange of matter and energy (metabolism).
As a result of metabolism (metabolism), a large number of metabolic products (metabolites) enter the biological internal environment of our body, the content of which in a healthy person varies slightly and amounts to homeostasis internal media of the body (blood, serum, cerebrospinal fluid, urine, digestive juices, etc.).
Almost any disease begins with damage (violation) of one reaction in the metabolism of the cell, and then it spreads to the tissue, organ and the whole organism. Violation of metabolism leads to a violation of homeostasis in the biological fluids of the human body, which is accompanied by a change in biochemical parameters.
The great importance of clinical and biochemical methods for the study of biological fluids is great in medicine and is important for the training of medical laboratory technicians. Suffice it to recall that about 1000 metabolic parameters can be determined only in human blood using modern methods of biochemical research.
Biochemical indicators of biological media of the human body are widely used for:
1. making a diagnosis of a disease, especially a differential diagnosis;
2. choice of treatment method;
3. control over the correctness of the prescribed treatment;
4. the results of biochemical analyzes serve as one of the criteria for the cure of the pathological process;
5. screening (detection of the disease at the preclinical stage);
6.monitoring (monitoring the course of the disease and the result of treatment);
7. prognosis (information about the possible outcome of the disease).
The explosive growth of biochemistry has led it to subdivide into different branches: clinical biochemistry, molecular biochemistry, sports biochemistry, and human biochemistry.
In the process of mastering the discipline "Fundamentals of biochemistry with methods of clinical and biochemical research" we face tasks of medical biochemistry which consists in studying:
1. the structure and functions of biomolecules that make up the tissues of the body.
2. Arrangements:
Receipt of plastic and biologically active substances into the internal environment of the body;
Transformation of incoming monomers into biopolymers specific to a given organism;
release, accumulation and use of energy in the cell;
Formation and excretion of end products of decomposition of substances in the body;
Reproduction and transmission of hereditary characteristics of the body;
regulation of all these processes.
The main focus of our course will be on the study of methods of clinical and biochemical research, which consist of stages.
2 Amino acids that make up proteins, their structure and properties. biological
the role of amino acids. Peptides.
Proteins are polymeric molecules in which amino acids serve as monomers. Only 20-AA is found in human proteins.
A. Structure and properties of amino acids
1. General structural features of amino acids that make up proteins
A common structural feature of AA is the presence of amino and carboxyl groups connected to the same carbon atom. R - amino acid radical - in the simplest case, it is represented by a hydrogen atom (glycine), but it can also have a more complex structure.
In aqueous solutions at neutral pH - AA exist in the form of bipolar ions.
Unlike the 19 others - AA, proline is an imino acid, the radical of which is connected both to the carbon atom and to the amino group, as a result of which the molecule acquires a cyclic structure.
19 out of 20 AAs contain an asymmetric carbon atom in the α-position, to which 4 different substituent groups are attached. As a result, these AAs can occur in nature in two different isomeric forms, L and D. An 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 spontaneously and non-enzymatically transform over a long period of time into an equimolar mixture of L- and D-isomers. This process is called racemization. The racemization of each L-amino acid at a given temperature proceeds at a certain rate. This circumstance can be used to determine the age of people and animals. So, in the hard enamel of the teeth there is a dentin protein, in which L-aspartate passes into the D-isomer at the temperature of the human body at a rate of 0.01% per year. During the period of tooth formation, the dentin contains only the L-isomer, so the age of the subject can be calculated from the content of D-aspartate.
All 20 AAs 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 the chemical structure, AA can be divided into aliphatic, aromatic and heterocyclic.
Aliphatic radicals may contain functional groups that give them specific properties: carboxyl (-COOH), amino (-NH 2), thiol (-SH), amide (-CO-NH 2), hydroxyl (-OH) and guanidine groups.
Amino acid names can be constructed from substitutional nomenclature, but trivial names are usually used.
3. Classification of amino acids according to the solubility of their radicals in water
AK with non-polarR: radicals having aliphatic hydrocarbon chains (radicals ala, val, leu, iso, pro and meth) and aromatic rings (radicals phene and tri).
AK with polar unchargedR: these radicals are better than hydrophobic radicals, soluble in water, tk. they contain polar functional groups that form hydrogen bonds with water. These include ser, tre and tyr, having hydroxyl groups, asn and hln, containing amide groups, and cis with its thiol group.
Cysteine and tyrosine contain thiol and hydroxyl groups, respectively, capable of dissociating with the formation of H + , but at a pH of about 7.0, maintained in cells, these groups practically do not dissociate.
AK with polar negatively chargedR: about include asn and hln amino acids having an additional carboxyl group in the radical, dissociating at pH 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.
AK with polar positively chargedR:
α-Amino acids can be covalently linked to each other via 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.
1. The structure of the peptide. 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 that make up 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 commonly referred to as proteins. However, these names are arbitrary, since the term "protein" is often used to refer to a polypeptide containing less than 50 amino acid residues. For example, the hormone glucagon, which consists of 29 amino acids, is called a protein hormone.
The amino acid monomers that make up proteins are called "amino acid residues". An amino acid residue having a free amino group is called N-terminal and is written on the left, and having a free α-carboxyl group is called C-terminal and is written on the right. Peptides are written and read from the N-terminus. The chain of repeating atoms in the -NH-CH-CO-polypeptide chain is called "peptide backbone".
When naming a polypeptide, the suffix -il is added to the abbreviated name of amino acid residues, except for the C-terminal amino acid. For example, Ser-Gly-Pro-Ala tetrapeptide is read as serylglycylprolylalanine.
The peptide bond formed by the imino group of proline differs from other peptide bonds, since the nitrogen atom of the peptide group is bonded not to hydrogen, but to a radical.
Peptides differ in amino acid composition, number and order of amino acids
3 The primary structure of proteins. Peptide bond, its characteristics (strength, multiplicity, coplanarity, cis-, trans-isomerism). The importance of the primary structure for the normal functioning of proteins (on the example of hemoglobin S).
Primary Structure- a concept denoting the sequence of amino acid residues in a protein Peptide bond - the main type of bond that determines the primary structure It is also possible that there are disulfide bonds between two cysteine residues in one polypeptide chain with the formation of cystine. The same bond (disulfide bridge) can also occur between cysteine residues belonging to different polypeptide chains in a protein molecule, a copolymer formation.
Amino acid residues in the peptide chain of proteins do not alternate randomly, but are arranged in a certain order. The linear sequence of amino acid residues in a polypeptide chain is called "primary structure of a protein".
The primary structure of each individual protein is encoded in a section of DNA called a gene. In the process of protein synthesis, the information contained in the gene is first copied to mRNA, and then, using mRNA as a template, the primary structure of the protein is assembled on the ribosome.
Each of the 50,000 individual proteins in the human body has a unique primary structure for that protein. All molecules of a given individual protein have the same alternation of amino acid residues in the protein, which primarily distinguishes this individual protein from any other
Many of us know that proteins are necessary for the body, as they contain amino acids. But not everyone understands what these elements are and why their presence in the diet is so important. Today we will find out how many amino acids are included in how they are classified and what function they perform.
What are amino acids?
So, amino acids (aminocarboxylic to-you) are organic compounds that are the main element that forms the structure of the protein. Proteins, in turn, take part in all physiological processes of the human body. They form bones, tendons, ligaments, internal organs, muscles, nails and hair. Proteins become part of the body in the process of synthesis of amino acids that come with food. Therefore, it is not protein that is an important nutrient, but amino acids. And not all proteins are equally useful, because each of them has its own unique composition of these same acids.
Quite complicated, let's consider it at a basic level. We know that aminocarboxylic acids are the building blocks of the building called protein and the metropolis called man. However, not all proteins have exactly the elements that we need. If you look at a protein under a microscope, you can see a chain of amino acids connected by peptide bonds. Roughly speaking, the links of this chain serve as a repair and building material in our body.
Surprisingly, there was a time when scientists didn't know how many different amino acids are in proteins. Most of them were opened in the 19th and the rest in the 20th century. It took scientists 119 years to finally answer the question: "How many amino acids are in a protein?" The structure of each of them was studied even longer.
To date, it is known that 20 proteinogenic aminocarboxylic acids are necessary for the normal functioning of the human body. These twenty are often called major acids. From the point of view of chemistry, they are classified according to many criteria. But ordinary people are closest to the classification according to the ability of acids to be synthesized in our body. On this basis, amino acids are interchangeable and irreplaceable.
This classification has some drawbacks. For example, arginine is considered essential in some physiological states, but it can be synthesized by the body. And histidine is replenished in such small quantities that it still needs to be taken with food.
Now that we know how many types of amino acids are included in proteins, let's take a closer look at both types.
Irreplaceable (essential)
As you already understood, these substances cannot be synthesized by the body on their own, so they must be consumed with food. The main amount of essential organic acids is found in animal proteins. When the body lacks one or another element, it begins to take it from the muscle tissue. This class consists of 8 acids. Let's get acquainted with each of them.
Leucine
This acid is responsible for the restoration and protection of muscle tissue, skin and bones. It is thanks to leucine that the growth hormone is released. In addition, this organic acid regulates blood sugar levels and promotes fat burning. It is found in meat, nuts, legumes, brown rice and wheat grains. Lecithin stimulates and therefore promotes muscle building.
Isoleucine
This acid speeds up energy production, which is why athletes love it so much. After exhausting workouts, it helps to quickly restore muscle fibers. Isoleucine relieves the so-called krepatura, takes part in the formation of hemoglobin and regulates the amount of sugar. Most isoleucine is found in meat, fish, eggs, nuts, peas and soy.
Lysine
This amino acid plays an important role in the functioning of the immune system. Its main task is the synthesis of antibodies that protect our body from the effects of viruses and allergens. In addition, lysine regulates the process of bone tissue and collagen renewal, as well as growth hormones. This organic acid can be found in foods such as: eggs, potatoes, red meat, fish and dairy products.
Phenylalanine
This alpha amino acid is responsible for the normal functioning of the central nervous system. Its deficiency in the body leads to bouts of depression and chronic diseases. Phenylalanine helps us concentrate and remember the right information. It is part of drugs used in the treatment of mental disorders, including Parkinson's disease. It has a positive effect on the functioning of the liver and pancreas. Amino acid found in: nuts, mushrooms, chicken, dairy products, bananas, apricots and Jerusalem artichoke.
Methionine
Few people know how many amino acids are in the protein, but many people know that methionine actively burns adipose tissue. But this is not all the useful properties of this acid. It affects the endurance and performance of a person. If it is not enough in the body, it can immediately be understood by the skin and nails. Methionine is found in foods such as: meat, fish, sunflower seeds, legumes, onions, garlic and dairy products.
Threonine
In an effort to find out how many amino acids are in a protein, scientists discovered a substance such as threonine, one of the last. But it is very useful for a person. Threonine is responsible for all the most important systems of the human body, namely the nervous, immune and cardiovascular systems. The first sign of its deficiency is problems with teeth and bones. Most people get threonine from dairy products, meat, mushrooms, vegetables and cereals.
tryptophan
Another important ingredient. It is responsible for the synthesis of serotonin, which is often called the feel-good hormone. Tryptophan deficiency can be detected by sleep disorders, appetite. This acid also regulates respiratory function and blood pressure. It is found mainly in: seafood, red meat, poultry, dairy products and wheat.
Valine
Performs the function of repairing damaged fibers and monitors metabolic processes in the muscles. Under heavy loads, it can have a stimulating effect. It also plays a role in human mental activity. Helps in the treatment of the liver and brain from the negative effects of alcohol and drugs. A person can get valine from: meat, mushrooms, soy, dairy, and peanuts.
It is noteworthy that 70% of all organic acids in our body are occupied by only three amino acids: leucine, isoleucine and valine. Therefore, they are considered the most important in ensuring the normal functioning of the body. In sports nutrition, they even isolated a special BCAA complex that contains precisely these three acids.
We continue to answer the question of how many major amino acids are included in the protein, and move on to the interchangeable representatives of the class.
Interchangeable
The main difference of this group is that all its representatives can be formed in the body by endogenous synthesis. The word "replaceable" misleads many. Therefore, often ignorant people say that these amino acids do not have to be consumed with food. Of course it is not! Replaceable acids, as well as essential ones, must be included in the daily diet. They can indeed be formed from other substances. But this only happens when the diet is incorrect. Then part of the useful substances and essential acids is spent on the reconstruction of non-essential acids. Therefore, it is not entirely favorable for the body. Let's analyze the essential acids included in the "major twenty".
Alanine
Helps accelerate the metabolism of carbohydrates and the removal of toxins from the liver. It is found in foods such as: meat, poultry, eggs, fish and dairy products.
Aspartic acid
It is considered a universal fuel for our body, as it significantly improves metabolism. It is found in milk, cane sugar, poultry and beef.
Asparagine
Trying to answer the question: "How many amino acids are included in the composition of the protein?", Scientists first of all discovered asparagine. It was back in 1806. This acid is involved in improving the functioning of the nervous system. It is found in all animal proteins, as well as nuts, potatoes and cereals.
Histidine
It is an important building block of all internal organs. It plays an almost key role in the formation of red and white blood cells. It has a positive effect on the immune system and sexual function. Due to the wide range of applications, histidine reserves in the body are rapidly depleted. Therefore, it is important to take it with food. Found in meat, dairy and cereal products.
Serene
Stimulates the brain and central nervous system. It is found in foods such as: meat, soy, cereals, peanuts.
Cysteine
This amino acid in the body is responsible for the synthesis of keratin. Without it, there would be no healthy nails, hair and skin. Found in foods such as: meat, eggs, red peppers, garlic, onions and broccoli.
Arginine
Speaking about how many proteinogenic amino acids are included in proteins and what functions they perform, we were convinced that each of them is important for the body. However, there are acids that, according to experts, are considered the most significant. These include arginine. It is responsible for the healthy functioning of muscles, joints, skin and liver, and also strengthens the immune system and burns fat. Arginine is often used by bodybuilders and those who wish to lose weight as part of supplements. It occurs naturally in meat, nuts, milk, cereals, and gelatin.
Glutamic acid
It is an important element for the healthy functioning of the brain and spinal cord. Often sold as a monosodium glutamate supplement. Found in eggs, meat, dairy products, fish, carrots, corn, tomatoes, and spinach.
Glutamine
Needed in protein for muscle growth and support. It is also the "fuel" of the brain. In addition, glutamine removes from the liver everything that comes there with unhealthy food. Cooking denatures the acid, so parsley and spinach need to be eaten raw to make up for it.
Glycine
Helps blood to clot and glucose to be converted into energy. It is found in meat, fish, legumes and milk.
Proline
Responsible for collagen synthesis. With a lack of proline in the body, problems with the joints begin. It is found mainly in animal proteins, therefore it is perhaps the only substance that people who do not eat meat face a lack of.
Tyrosine
Responsible for regulating blood pressure and appetite. With a lack of this acid, a person suffers from rapid fatigue. To avoid such problems, you need to eat bananas, seeds, nuts and avocados.
Foods rich in amino acids
Now you know how many amino acids are in protein. The functions and location of each of them are also known to you. Let's note the main products, using which, you can not worry about the balance of nutrition in terms of amino acids.
Eggs. They are perfectly absorbed by the body, give it a large amount of amino acids and provide protein nutrition.
Milk products. They are able to provide a person with many useful substances, the spectrum of which, by the way, is not limited to organic acids.
Meat. Perhaps the first source of protein and its constituent substances.
Fish. Rich in protein and perfectly digestible by the body.
Many are absolutely sure that without animal products it is impossible to provide the body with the proper amount of protein. This is completely false. And the proof of this is the huge number of vegetarians with excellent physical shape. Among plant foods, the main sources of amino acids are: legumes, nuts, cereals, seeds.
Conclusion
Today we learned how many amino acids are in protein. Groups of substances and a detailed description of their representatives will help you navigate the preparation of a healthy diet.
Proteins form the material basis of the chemical activity of the cell. The functions of proteins in nature are universal. name proteins, most accepted in the domestic literature, corresponds to the term proteins(from Greek. proteios- first). To date, great progress has been made in establishing the relationship between the structure and functions of proteins, the mechanism of their participation in the most important processes of the body's vital activity, and in understanding the molecular basis of the pathogenesis of many diseases.
Depending on the molecular weight, peptides and proteins are distinguished. Peptides have a lower molecular weight than proteins. For peptides, a regulatory function is more characteristic (hormones, enzyme inhibitors and activators, ion carriers through membranes, antibiotics, toxins, etc.).
12.1. α -Amino acids
12.1.1. Classification
Peptides and proteins are built from α-amino acid residues. The total number of naturally occurring amino acids exceeds 100, but some of them are found only in a certain community of organisms, the 20 most important α-amino acids are constantly found in all proteins (Scheme 12.1).
α-Amino acids are heterofunctional compounds whose molecules contain both an amino group and a carboxyl group at the same carbon atom.
Scheme 12.1.Essential α-amino acids*
* Abbreviations are used only for recording amino acid residues in peptide and protein molecules. ** Essential amino acids.
The names of α-amino acids can be constructed according to substitutional nomenclature, but their trivial names are more commonly used.
The trivial names of α-amino acids are usually associated with sources of isolation. Serine is part of silk fibroin (from lat. serieus- silky); tyrosine was first isolated from cheese (from the Greek. Tyros- cheese); glutamine - from cereal gluten (from it. Gluten- glue); aspartic acid - from asparagus sprouts (from lat. asparagus- asparagus).
Many α-amino acids are synthesized in the body. Some amino acids necessary for protein synthesis are not formed in the body and must be supplied from outside. These amino acids are called indispensable(see diagram 12.1).
Essential α-amino acids include:
valine isoleucine methionine tryptophan
leucine lysine threonine phenylalanine
α-Amino acids are classified in several ways, depending on the feature underlying their division into groups.
One of the classification features is the chemical nature of the radical R. According to this feature, amino acids are divided into aliphatic, aromatic and heterocyclic (see Scheme 12.1).
Aliphaticα -amino acids. This is the largest group. Within it, amino acids are subdivided using additional classification features.
Depending on the number of carboxyl groups and amino groups in the molecule, there are:
Neutral amino acids - one NH group each 2 and COOH;
Basic amino acids - two NH groups 2 and one group
COOH;
Acidic amino acids - one NH 2 group and two COOH groups.
It can be noted that in the group of aliphatic neutral amino acids, the number of carbon atoms in the chain does not exceed six. At the same time, there is no amino acid with four carbon atoms in the chain, and amino acids with five and six carbon atoms have only a branched structure (valine, leucine, isoleucine).
The aliphatic radical may contain "additional" functional groups:
Hydroxyl - serine, threonine;
Carboxyl - aspartic and glutamic acids;
Thiol - cysteine;
Amide - asparagine, glutamine.
aromaticα -amino acids. This group includes phenylalanine and tyrosine, constructed in such a way that the benzene rings in them are separated from the common α-amino acid fragment by a methylene group -CH 2-.
Heterocyclic α -amino acids. Related to this group, histidine and tryptophan contain heterocycles - imidazole and indole, respectively. The structure and properties of these heterocycles are discussed below (see 13.3.1; 13.3.2). The general principle for constructing heterocyclic amino acids is the same as for aromatic ones.
Heterocyclic and aromatic α-amino acids can be considered as β-substituted derivatives of alanine.
The amino acid also belongs to the heroocyclic proline, in which the secondary amino group is included in the composition of the pyrrolidine
In the chemistry of α-amino acids, much attention is paid to the structure and properties of "side" radicals R, which play an important role in the formation of the structure of proteins and the performance of their biological functions. Of great importance are such characteristics as the polarity of "side" radicals, the presence of functional groups in the radicals, and the ability of these functional groups to ionize.
Depending on the side radical, amino acids are isolated with non-polar(hydrophobic) radicals and amino acids c polar(hydrophilic) radicals.
The first group includes amino acids with aliphatic side radicals - alanine, valine, leucine, isoleucine, methionine - and aromatic side radicals - phenylalanine, tryptophan.
The second group includes amino acids that have polar functional groups in the radical that are capable of ionization (ionic) or are not able to transform into an ionic state (nonionic) under the conditions of the organism. For example, in tyrosine the hydroxyl group is ionic (has a phenolic nature), in serine it is nonionic (has an alcohol nature).
Polar amino acids with ionogenic groups in the radicals under certain conditions can be in the ionic (anionic or cationic) state.
12.1.2. stereoisomerism
The basic type of construction of α-amino acids, i.e., the bond of one and the same carbon atom with two different functional groups, a radical and a hydrogen atom, in itself predetermines the chirality of the α-carbon atom. The exception is the simplest amino acid glycine H 2 NCH 2 COOH without a center of chirality.
The configuration of α-amino acids is determined by the configuration standard - glyceraldehyde. The location of the amino group in the standard Fischer projection formula on the left (similar to the OH group in l-glycerol aldehyde) corresponds to the l-configuration, on the right - to the d-configuration of the chiral carbon atom. By R, In the S system, the α-carbon atom of all α-amino acids of the l-series has the S-, and the d-series has the R-configuration (the exception is cysteine, see 7.1.2).
Most α-amino acids contain one asymmetric carbon atom in the molecule and exist as two optically active enantiomers and one optically inactive racemate. Almost all natural α-amino acids belong to the l-series.
The amino acids isoleucine, threonine, and 4-hydroxyproline each contain two centers of chirality per molecule.
Such amino acids can exist as four stereoisomers, which are two pairs of enantiomers, each of which forms a racemate. Only one of the enantiomers is used to build animal proteins.
The stereoisomerism of isoleucine is similar to the stereoisomerism of threonine discussed earlier (see 7.1.3). Of the four stereoisomers, proteins include l-isoleucine with the S-configuration of both asymmetric carbon atoms С-α and С-β. The names of the other pair of enantiomers that are diastereomers with respect to leucine use the prefix Hello-.
Breakdown of racemates. The source of obtaining α-amino acids of the l-series are proteins, which are subjected to hydrolytic cleavage for this. Due to the great need for individual enantiomers (for the synthesis of proteins, medicinal substances, etc.), chemical methods for the cleavage of synthetic racemic amino acids. Preferred enzymatic digestion method using enzymes. Currently, chromatography on chiral sorbents is used to separate racemic mixtures.
12.1.3. Acid-base properties
Amphotericity of amino acids is due to acidic (COOH) and basic (NH 2) functional groups in their molecules. Amino acids form salts with both alkalis and acids.
In the crystalline state, α-amino acids exist as dipolar ions H3N+ - CHR-COO- (commonly used notation
structure of the amino acid in the non-ionized form is for convenience only).
In an aqueous solution, amino acids exist as an equilibrium mixture of dipolar ions, cationic and anionic forms.
The equilibrium position depends on the pH of the medium. All amino acids are dominated by cationic forms in strongly acidic (pH 1–2) and anionic forms in strongly alkaline (pH>11) media.
The ionic structure determines a number of specific properties of amino acids: a high melting point (above 200 °C), solubility in water, and insolubility in nonpolar organic solvents. The ability of most amino acids to dissolve well in water is an important factor in ensuring their biological functioning; it is associated with the absorption of amino acids, their transport in the body, etc.
A fully protonated amino acid (cationic form), according to the Brønsted theory, is a dibasic acid,
Donating one proton, such a dibasic acid turns into a weak monobasic acid - a dipolar ion with one acid group NH 3 + . Deprotonation of the dipolar ion results in the anionic form of the amino acid, the carboxylate ion, which is a Bronsted base. Values characterize
the acidic properties of the carboxyl group of amino acids usually range from 1 to 3; values pK a2 characterizing the acidity of the ammonium group - from 9 to 10 (Table 12.1).
Table 12.1.Acid-base properties of the most important α-amino acids
The equilibrium position, i.e., the ratio of different forms of amino acids, in an aqueous solution at certain pH values depends significantly on the structure of the radical, mainly on the presence of ionogenic groups in it, which play the role of additional acidic and basic centers.
The pH value at which the concentration of dipolar ions is maximum, and the minimum concentrations of cationic and anionic forms of the amino acid are equal, is calledisoelectric point (p/).
Neutralα -amino acids. These amino acids matterpIslightly lower than 7 (5.5-6.3) due to the greater ability to ionize the carboxyl group under the influence of the -/- effect of the NH 2 group. For example, alanine has an isoelectric point at pH 6.0.
Sourα -amino acids. These amino acids have an additional carboxyl group in the radical and are in a fully protonated form in a strongly acidic medium. Acidic amino acids are tribasic (according to Bröndsted) with three meaningspK a,as seen in the example of aspartic acid (p/ 3.0).
For acidic amino acids (aspartic and glutamine), the isoelectric point is at a pH well below 7 (see Table 12.1). In the body at physiological pH values (for example, blood pH 7.3-7.5), these acids are in the anionic form, since both carboxyl groups are ionized in them.
Mainα -amino acids. In the case of basic amino acids, the isoelectric points are in the pH region above 7. In a strongly acidic medium, these compounds are also tribasic acids, the stages of ionization of which are shown using the example of lysine (p/ 9.8).
In the body, the basic amino acids are in the form of cations, that is, they have both amino groups protonated.
In general, none of the α-amino acids in vivois not located at its isoelectric point and does not fall into the state corresponding to the lowest solubility in water. All amino acids in the body are in ionic form.
12.1.4. Analytically important reactions α -amino acids
α-Amino acids, as heterofunctional compounds, enter into reactions characteristic of both the carboxyl and amino groups. Some of the chemical properties of amino acids are due to the functional groups in the radical. This section discusses reactions that are of practical importance for the identification and analysis of amino acids.
Etherification.The reaction of amino acids with alcohols in the presence of an acid catalyst (for example, gaseous hydrogen chloride) gives esters in the form of hydrochlorides in good yield. To isolate the free esters, the reaction mixture is treated with gaseous ammonia.
Esters of amino acids do not have a dipolar structure, therefore, unlike the original acids, they dissolve in organic solvents and are volatile. Thus, glycine is a crystalline substance with a high melting point (292°C), while its methyl ester is a liquid with a boiling point of 130°C. The analysis of amino acid esters can be carried out using gas-liquid chromatography.
Reaction with formaldehyde. Of practical importance is the reaction with formaldehyde, which underlies the quantitative determination of amino acids by the method formal titration(Sorensen method).
The amphoteric nature of amino acids does not allow their direct titration with alkali for analytical purposes. When amino acids react with formaldehyde, relatively stable amino alcohols (see 5.3) are obtained - N-hydroxymethyl derivatives, the free carboxyl group of which is then titrated with alkali.
quality reactions. A feature of the chemistry of amino acids and proteins is the use of numerous qualitative (color) reactions, which previously formed the basis of chemical analysis. At present, when studies are carried out using physicochemical methods, many qualitative reactions continue to be used to detect α-amino acids, for example, in chromatographic analysis.
Chelating. With heavy metal cations, α-amino acids as bifunctional compounds form intra-complex salts, for example, with freshly prepared copper (11) hydroxide under mild conditions, well-crystallized chelate salts are obtained.
blue copper(11) salts (one of the non-specific methods for detecting α-amino acids).
ninhydrin reaction. The general qualitative reaction of α-amino acids is the reaction with ninhydrin. The reaction product has a blue-violet color, which is used for visual detection of amino acids on chromatograms (on paper, in a thin layer), as well as for spectrophotometric determination on amino acid analyzers (the product absorbs light in the 550-570 nm region).
Deamination. Under laboratory conditions, this reaction is carried out by the action of nitrous acid on α-amino acids (see 4.3). In this case, the corresponding α-hydroxy acid is formed and gaseous nitrogen is released, the volume of which is used to judge the amount of the reacted amino acid (Van Slyke method).
xantoprotein reaction. This reaction is used to detect aromatic and heterocyclic amino acids - phenylalanine, tyrosine, histidine, tryptophan. For example, under the action of concentrated nitric acid on tyrosine, a yellow-colored nitro derivative is formed. In an alkaline medium, the color becomes orange due to the ionization of the phenolic hydroxyl group and an increase in the contribution of the anion to conjugation.
There are also a number of private reactions that allow the detection of individual amino acids.
tryptophan detected by reaction with p-(dimethylamino)benzaldehyde in sulfuric acid medium by the emerging red-violet color (Ehrlich reaction). This reaction is used to quantify tryptophan in protein digestion products.
Cysteine is detected by several qualitative reactions based on the reactivity of the mercapto group it contains. For example, when a protein solution with lead acetate (CH3COO)2Pb is heated in an alkaline medium, a black precipitate of lead sulfide PbS is formed, which indicates the presence of cysteine in proteins.
12.1.5. Biologically important chemical reactions
In the body, under the action of various enzymes, a number of important chemical transformations of amino acids are carried out. Such transformations include transamination, decarboxylation, elimination, aldol cleavage, oxidative deamination, and oxidation of thiol groups.
transamination is the main pathway for the biosynthesis of α-amino acids from α-oxo acids. The donor of the amino group is an amino acid present in cells in sufficient quantity or excess, and its acceptor is α-oxo acid. In this case, the amino acid is converted into an oxo acid, and the oxo acid into an amino acid with the corresponding structure of the radicals. As a result, transamination is a reversible process of interchange of amino and oxo groups. An example of such a reaction is the preparation of l-glutamic acid from 2-oxoglutaric acid. The donor amino acid can be, for example, l-aspartic acid.
α-Amino acids contain an electron-withdrawing amino group in the α-position to the carboxyl group (more precisely, the protonated amino group NH 3 +), in connection with which they are capable of decarboxylation.
eliminationcharacteristic of amino acids, in which the side radical in the β-position to the carboxyl group contains an electron-withdrawing functional group, for example, hydroxyl or thiol. Their cleavage leads to intermediate reactive α-enamino acids, which easily transform into tautomeric imino acids (an analogy with keto-enol tautomerism). α-Imino acids, as a result of hydration at the C=N bond and subsequent elimination of the ammonia molecule, are converted into α-oxo acids.
This type of transformation is called elimination-hydration. An example is the preparation of pyruvic acid from serine.
Aldol cleavage occurs in the case of α-amino acids, which contain a hydroxyl group in the β-position. For example, serine is cleaved to form glycine and formaldehyde (the latter is not released in free form, but immediately binds to the coenzyme).
Oxidative deamination may involve enzymes and the coenzyme NAD+ or NADP+ (see 14.3). α-Amino acids can be converted to α-oxo acids not only through transamination, but also through oxidative deamination. For example, from l-glutamic acid, α-oxoglutaric acid is formed. The first stage of the reaction involves dehydrogenation (oxidation) of glutamic acid to α-iminoglutaric acid.
acids. At the second stage, hydrolysis occurs, as a result of which α-oxoglutaric acid and ammonia are obtained. The hydrolysis step proceeds without the participation of the enzyme.
Reductive amination of α-oxo acids proceeds in the opposite direction. α-Oxoglutaric acid, which is always contained in cells (as a product of carbohydrate metabolism), is converted in this way into L-glutamic acid.
Oxidation of thiol groups underlies the interconversions of cysteine and cystine residues, providing a number of redox processes in the cell. Cysteine, like all thiols (see 4.1.2), is easily oxidized to form a disulfide, cystine. The disulfide bond in cystine is easily reduced to form cysteine.
Due to the ability of the thiol group to easily oxidize, cysteine performs a protective function when exposed to substances with a high oxidizing ability. In addition, he was the first drug to show an anti-radiation effect. Cysteine is used in pharmaceutical practice as a drug stabilizer.
The conversion of cysteine to cystine leads to the formation of disulfide bonds, for example, in reduced glutathione
(see 12.2.3).
12.2. Primary structure of peptides and proteins
It is conditionally believed that peptides contain up to 100 amino acid residues in a molecule (which corresponds to a molecular weight of up to 10 thousand), and proteins - more than 100 amino acid residues (molecular weight from 10 thousand to several million).
In turn, in the group of peptides it is customary to distinguish oligopeptides(low molecular weight peptides) containing no more than 10 amino acid residues in the chain, and polypeptides, the chain of which includes up to 100 amino acid residues. Macromolecules with the number of amino acid residues approaching or slightly exceeding 100 are not distinguished by the concepts of polypeptides and proteins, these terms are often used as synonyms.
A peptide and protein molecule can formally be represented as a product of the polycondensation of α-amino acids, which proceeds with the formation of a peptide (amide) bond between monomer units (Scheme 12.2).
The structure of the polyamide chain is the same for the entire variety of peptides and proteins. This chain has an unbranched structure and consists of alternating peptide (amide) groups -CO-NH- and fragments -CH(R)-.
One end of the chain containing an amino acid with a free NH group 2, called the N-terminus, the other - the C-terminus,
Scheme 12.2.The principle of building a peptide chain
which contains an amino acid with a free COOH group. Peptide and protein chains are written from the N-terminus.
12.2.1. The structure of the peptide group
In the peptide (amide) group -СО-NH-, the carbon atom is in the state of sp2 hybridization. The lone pair of electrons of the nitrogen atom enters conjugation with the π-electrons of the C=O double bond. From the standpoint of the electronic structure, the peptide group is a three-center p, π-conjugated system (see 2.3.1), in which the electron density is shifted towards the more electronegative oxygen atom. The C, O, and N atoms forming a conjugated system are in the same plane. The electron density distribution in the amide group can be represented using boundary structures (I) and (II) or electron density shift due to the +M- and -M-effects of the NH and C=O groups, respectively (III).
As a result of conjugation, some alignment of the bond lengths occurs. The C=O double bond lengthens to 0.124 nm against the usual length of 0.121 nm, and the C-N bond becomes shorter - 0.132 nm compared to 0.147 nm in the usual case (Fig. 12.1). The planar conjugated system in the peptide group makes it difficult to rotate around the C-N bond (the rotation barrier is 63-84 kJ/mol). Thus, the electronic structure predetermines a fairly rigid flat the structure of the peptide group.
As can be seen from fig. 12.1, α-carbon atoms of amino acid residues are located in the plane of the peptide group on opposite sides of the C-N bond, i.e., in a more favorable trans position: the side radicals R of amino acid residues in this case will be the most distant from each other in space.
The polypeptide chain has a surprisingly uniform structure and can be represented as a series of angled
Rice. 12.1.Planar arrangement of the peptide group -CO-NH- and α-carbon atoms of amino acid residues
to each other of the planes of peptide groups interconnected through α-carbon atoms by Сα-N and Сα-Сsp bonds 2 (Fig. 12.2). Rotation around these single bonds is very limited due to difficulties in the spatial arrangement of side radicals of amino acid residues. Thus, the electronic and spatial structure of the peptide group largely determines the structure of the polypeptide chain as a whole.
Rice. 12.2.Mutual position of the planes of peptide groups in the polypeptide chain
12.2.2. Composition and amino acid sequence
With a uniformly constructed polyamide chain, the specificity of peptides and proteins is determined by two most important characteristics - amino acid composition and amino acid sequence.
The amino acid composition of peptides and proteins is the nature and quantitative ratio of their constituent α-amino acids.
The amino acid composition is established by analyzing peptide and protein hydrolysates, mainly by chromatographic methods. Currently, such analysis is carried out using amino acid analyzers.
Amide bonds are capable of hydrolyzing in both acidic and alkaline conditions (see 8.3.3). Peptides and proteins are hydrolyzed to form either shorter chains - this is the so-called partial hydrolysis, or a mixture of amino acids (in ionic form) - complete hydrolysis. Typically, hydrolysis is carried out in an acidic environment, since many amino acids are unstable under alkaline hydrolysis conditions. It should be noted that the amide groups of asparagine and glutamine also undergo hydrolysis.
The primary structure of peptides and proteins is the amino acid sequence, that is, the order of alternation of α-amino acid residues.
The primary structure is determined by sequential cleavage of amino acids from either end of the chain and their identification.
12.2.3. Structure and nomenclature of peptides
Peptide names are built by sequentially listing amino acid residues, starting from the N-terminus, with the addition of a suffix-il, except for the last C-terminal amino acid, for which its full name is retained. In other words, the names
amino acids that have entered into the formation of a peptide bond due to their “own” COOH group end in the name of the peptide with -il: alanyl, valyl, etc. (for residues of aspartic and glutamic acids, the names "aspartyl" and "glutamyl" are used, respectively). The names and symbols of amino acids indicate their belonging to l -row, unless otherwise specified ( d or dl).
Sometimes in the abbreviated notation with the symbols H (as part of the amino group) and OH (as part of the carboxyl group), the unsubstitution of the functional groups of the terminal amino acids is specified. This method is convenient to depict functional derivatives of peptides; for example, the amide of the above peptide at the C-terminal amino acid is written H-Asn-Gly-Phe-NH2.
Peptides are found in all organisms. Unlike proteins, they have a more heterogeneous amino acid composition; in particular, they quite often include amino acids d -series. Structurally, they are also more diverse: they contain cyclic fragments, branched chains, etc.
One of the most common representatives of tripeptides - glutathione- found in the body of all animals, in plants and bacteria.
Cysteine in the composition of glutathione determines the possibility of the existence of glutathione in both reduced and oxidized forms.
Glutathione is involved in a number of redox processes. It performs the function of a protein protector, i.e., a substance that protects proteins with free thiol groups SH from oxidation with the formation of disulfide bonds -S-S-. This applies to those proteins for which such a process is undesirable. Glutathione in these cases takes over the action of the oxidizing agent and thus "protects" the protein. During the oxidation of glutathione, intermolecular crosslinking of two tripeptide fragments occurs due to a disulfide bond. The process is reversible.
12.3. Secondary structure of polypeptides and proteins
High-molecular polypeptides and proteins, along with the primary structure, are also characterized by higher levels of organization, which are called secondary, tertiary and Quaternary structures.
The secondary structure is described by the spatial orientation of the main polypeptide chain, while the tertiary structure is described by the three-dimensional architecture of the entire protein molecule. Both the secondary and tertiary structure are associated with the ordered arrangement of the macromolecular chain in space. The tertiary and quaternary structure of proteins is discussed in the course of biochemistry.
It was shown by calculation that one of the most favorable conformations for the polypeptide chain is the arrangement in space in the form of a right-handed helix, called α-helix(Fig. 12.3, a).
The spatial arrangement of an α-helical polypeptide chain can be imagined by imagining that it wraps around a certain
Rice. 12.3.α-helical conformation of the polypeptide chain
cylinder (see Fig. 12.3, b). On average, there are 3.6 amino acid residues per turn of the helix, the helix pitch is 0.54 nm, and the diameter is 0.5 nm. The planes of two neighboring peptide groups are located at an angle of 108°, and the side radicals of amino acids are on the outer side of the helix, i.e., they are directed, as it were, from the surface of the cylinder.
The main role in fixing such a chain conformation is played by hydrogen bonds, which are formed in the α-helix between the carbonyl oxygen atom of each first and the hydrogen atom of the NH group of each fifth amino acid residue.
Hydrogen bonds are directed almost parallel to the axis of the α-helix. They keep the chain in a twisted state.
Typically, protein chains are not completely coiled, but only partially. Proteins such as myoglobin and hemoglobin contain fairly long α-helical regions, such as the myoglobin chain.
spiralized by 75%. In many other proteins, the proportion of helical regions in the chain may be small.
Another type of secondary structure of polypeptides and proteins is β-structure, also called folded sheet, or folded layer. Folded sheets contain elongated polypeptide chains connected by many hydrogen bonds between the peptide groups of these chains (Fig. 12.4). Many proteins simultaneously contain α-helical and β-sheet structures.
Rice. 12.4.The secondary structure of the polypeptide chain in the form of a folded sheet (β-structure)
There are only 20 basic amino acids. Their names are associated with random moments. All amino acids that are part of natural proteins are α-amino acids. This means that the amino and carboxyl groups are on the same carbon atom.
1. aminoacetic acid (glycine);
2. 
α-aminopropanoic acid (alanine);
3. 
α-aminopentanoic acid (valine);
4. 
α-aminoisocaproic acid (leucine);
5. 
α-amino-β-methylvaleric acid (isoleucine);
6. 
α-amino-β-hydroxypropanoic acid (serine);
7. 
α-amino-β-hydroxybutyric acid (threonine);
Sulfur-containing:
8. 
α-amino-β-mercaptopropanoic acid (cysteine);
9. 
α-amino-γ-methylthiobutyric acid (methionine);
10. 
α-aminosuccinic acid (aspartic acid);
11. 
aspartic acid amide (asparagine);
12. 
α-aminoglutaric acid (glutamic acid);
13. 
α-aminoglutaric acid amide (gutamine);
14. 
α, ε-diaminocaproic acid (leucine);
15. 
α-amino-δ-guanidylovaleric acid
(arginine);
Cyclic :
16. 
α-amino-β-phenylpropanoic acid (phenylalanine);
17. 
α-amino-β-para-hydroxyphenylproanoic acid (tyrosine);
18. 
α-amino-β-imidozolylpropanoic acid (histedine);
19. 
α-amino-β-indolylpropanoic acid (tryptophan);
20. 
α-tetrahydropyrolecarboxylic acid (proline).
All natural amino acids belong to the L-stereochemical series, D-series only as an exception in bacteria, as part of capsules to protect bacteria from the action of enzymes.
Lecture 3.
Each amino acid has its own unique physical and chemical properties - the isoelectric point, i.e. the pH of the medium at which the solution of this amino acid is electrically neutral. (q = 0).
If we consider such an acid in an aqueous medium, then dissociation occurs both in the acidic and in the basic type - a bipolar ion.
In the body of mammals, the liver contains the enzyme D-amino acid oxidase, which selectively destroys D-amino acids that come from food. D-amino acids have been found in some peptides of microorganisms. In addition, D-amino acids are part of a large number of antibiotics. For example, D-valine, D-leucine are part of the antibiotic borderidin, D-phenylalanine is part of borderidin-C, penicillin contains an unusual fragment D-dimethylcysteine.
The process of racimization (transition of D to L) does not occur enzymatically, therefore it is very slow. This is the basis for determining the age of mammals.
All amino acids have in their composition an amino and a carboxyl group, they have the properties of amines and carboxylic acids. In addition, α-amino acids are characterized ninhydrin reaction(common with proteins). With an alcohol solution of ninhydrin, a blue-violet color very quickly appears, with yellow propyne.
At the end of the 19th century, there was a controversy about how amino acids form a bond; if you take two amino acids and merge them together, you will never get a linear structure (due to thermodynamics, cyclization occurs). It was not possible to obtain a polypeptide in the 19th century.
Linear molecules won't work. From the point of view of thermodynamics, it is more advantageous to split off 2H 2 O than to form a linear molecule.
In 1888, the chemist Danilevsky suggested that proteins are polypeptides, linear molecules that are formed as a result of the action of the carboxyl group of one amino acid with the carboxyl group of another amino acid with the elimination of water and a dipeptide is formed:
An amide bond is formed (for proteins, a peptide bond), these peptide bonds are separated by only one carbon atom. Based biuret reaction Danilevsky made such a conclusion. This is the reaction of a protein solution with copper sulfate in an alkaline medium, a blue-violet color is formed, a chilate complex with copper ions is formed, as a result of the fact that the peptide bond in protein molecules has a specific structure. Due to keto-enol tautomerism, it is half double, half single. Typical reaction with Cu(OH) 2:
The biuret reaction is typical for biuret (Fig. 1), for malonamide (Fig. 2), proteins.
In order to finally prove that whites are polypeptides in 1901, Fischer synthesized a polypeptide, independently of him Hoffmann also synthesized a polypeptide:
Synthesis of a polypeptide according to Fischer:
The product gave a biuret reaction, was poorly soluble, had no biological activity, was cleaved by protolytic enzymes, and enzymes are specific biocatalysts that break down natural proteins, which means that this product has the same structure as natural proteins.
Currently, more than 2 thousand different proteins have been synthesized. The main thing in protein synthesis is the protection of the amino group and the activation of the carboxyl group so that the synthesis is directed. Amino groups are protected by acylation, for this they are treated with trichloroacetic acid anhydrides and a trifluoroacyl group is introduced, or treated according to Zeners (benzyl ester of chlorocarbonic acid).
For the synthesis of each particular polypeptide, for stitching a particular site can be carried out their own methods.
Protection by Zerves, activation by Curtius, unprotection by Beckman :
Solid-phase synthesis of polypeptides and proteins, a specific feature of polypeptide synthesis is a huge number of operations of the same type. A method has been developed by Robert Maryfilod . Monomers are amino acids that are used for synthesis, containing a protected amino group and activated carboxyl groups - synthons. Merifield proposed: fix the first monomer on a polymer resin (insoluble carrier) and all subsequent operations are carried out with a polypeptide growing on a polymer base, the next synthon and a reagent are added alternately to the resin to remove the terminal protective group. The chemical steps are punctuated by appropriate washes. Throughout the process, the polypeptide remains bound to the resin. This process can be easily automated by programming the change of flows through the column. Synthesizers are currently being developed. At the final stage of synthesis, the polypeptide is covalently bound to the resin, removed from this resin, and the protective group is removed. One of the biggest problems in solid phase synthesis is the racimization of amino acids during synthesis. This is especially dangerous in this synthesis, as There are no intermediate steps for isolating racimates. There are no methods of secession at the moment, but there are conditions for rationalization to be as small as possible. Merifield himself obtained several polypeptides by this method at once, bradykidin was obtained - a hormone with a vasodilating effect, angiotensin - a hormone that increases blood pressure, the enzyme ribonuclease, which catalyzes the hydrolysis of RNA.
The yield of products by this method is not significantly comparable with the methods that have been used before. With the help of automation, this method can be used on an industrial scale.
Each polypeptide has an N-terminus and another C-terminus. The amino acid that takes part changes the ending to il
Glycyl-valyl-tyrosyl-histedine-asparagyl-proline. To determine the amino acids in the polypeptide, it is necessary to carry out hydrolysis, it is carried out at 100 C for 24 hours with 6N hydrochloric acid. Further, the hydrolysis products are analyzed - separated by ion-exchange chromatography on a column of sulfonated polystyrene. Then washed with citrate buffer from the column. By the amount of eluent, it is judged which acids, i.e. acidic acids will be washed out first, and basic acids will be washed out last. In this way, it is possible to determine at what point which amino acid has passed, and the amount is determined photometrically using nindrin, this method can determine 1 μg. If it is necessary to determine 1 ng, fluoroscanin is used, it reacts with α-amino acids, forming a highly fluorescent compound. They determine which and how many amino acids are located, but the sequence of amino acids cannot be determined.
Fluoroslanin:
It's no secret that a person needs protein to maintain life at a high level - a kind of building material for body tissues; proteins contain 20 amino acids, the names of which are unlikely to say anything to an ordinary office worker. Every person, especially if we talk about women, has ever heard of collagen and keratin - these are proteins that are responsible for the appearance of nails, skin and hair.
Amino acids - what is it?
Amino acids (or aminocarboxylic acids; AMK; peptides) are organic compounds, 16% consisting of amines - organic derivatives of ammonium - which distinguishes them from carbohydrates and lipids. They are involved in protein biosynthesis by the body: in the digestive system, under the influence of enzymes, all proteins that come with food are destroyed to AMK. 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 interchangeable and irreplaceable; sometimes there is a third type - semi-replaceable (conditionally replaceable).
Non-essential amino acids
Non-essential amino acids are those that are both consumed with food and reproduced directly in the human body from other substances.
- Alanine is a monomer of biological compounds and proteins. Carries out one of the dominant pathways of glucogenesis, that is, it turns into glucose in the liver, and vice versa. A highly active participant in metabolic processes in the body.
- Arginine is an AMA that can be synthesized in the body of an adult, but not capable of being synthesized in the body of a child. Promotes the production of growth hormones and others. The only carrier of nitrogenous compounds in the body. Helps to increase muscle mass and reduce fat.
- Asparagine is a peptide involved in nitrogen metabolism. During the reaction with the enzyme asparaginase, it cleaves 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 to prevent and treat gastrointestinal diseases; is making a positive difference 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 a large volume 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 the elasticity of the skin.
- Serine - AMK that is contained in the 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 made 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 come from food.
- Valine is an AMA found in almost all proteins. Increases muscle coordination and reduces the body's sensitivity to temperature changes. Supports the hormone serotonin at a high level.
- Isoleucine is a natural anabolic that, in the process of oxidation, energizes muscle and brain tissue.
- Leucine is an amino acid that improves metabolism. It is a kind of "builder" of the protein structure.
- These three AMCs are part of the so-called BCAA complex, which is especially in demand among athletes. The substances of this group act as a source for increasing the volume of muscle mass, reducing fat mass and maintaining good health during particularly intense physical exertion.
- Lysine is a peptide that accelerates tissue regeneration, the production of hormones, enzymes and antibodies. Responsible for the strength of blood vessels, contained 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 the tendons. It has a very positive effect on the heart muscle and tooth enamel.
- Tryptophan - supports the 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, 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 subdivided based on the polarity of their side chain, that is, the 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, aspartic and glutamic acids are classified as polar, having a negative charge. Polar, having a positive charge, called arginine, histidine, lysine. Amino acids with polarity but no charge include directly cysteine, glutamine, serine, tyrosine, threonine, asparagine.
20 amino acids: formulas (table)
Amino acid | Abbreviation | |
Asparagine | ||
Aspartic acid | ||
Histidine | ||
Glutamine | ||
Glutamic acid | ||
Isoleucine | ||
Methionine | ||
tryptophan | ||
Phenylalanine | ||
Based on this, it can be noted that all 20 in the table above) have carbon, hydrogen, nitrogen and oxygen in their composition.
Amino acids: participation in the life of the cell
Aminocarboxylic acids are involved in the biological synthesis of proteins. Protein biosynthesis is the process of modeling a polypeptide ("poly" - many) chain from 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 (matrix RNA, or i-RNA - informational RNA - identically equal concepts), the nitrogenous base thymine is replaced by uracil. Further, according to the same principle, a transporting amino acid molecule is created to the site of synthesis. T-RNA is encoded by triplets (codons) (example: WAU), and if you know which nitrogenous bases a triplet represents, you can find out which amino acid it carries.
Food groups with the highest AUA content
Dairy products and eggs contain important substances such as valine, leucine, isoleucine, arginine, tryptophan, methionine and phenylalanine. Fish, 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 compiling a diet based on maintaining normal BUN, you should pay attention to squid and peas, and potatoes and cow's milk can be called the poorest in terms of peptide content.
Amino acid deficiency in vegetarianism
The fact that there are such amino acids that are found exclusively in animal products is a myth. Moreover, scientists have found that plant protein is absorbed by the human body better than animal. However, when choosing vegetarianism as a lifestyle, it is very important to follow the diet. The main problem is that one hundred grams of meat and the same amount of beans contain different amounts of AUA in percentage terms. At first, it is necessary to keep records of the content of amino acids in the food consumed, then this should reach automaticity.
How many amino acids should be consumed per day
In the modern world, absolutely all food products contain the nutrients necessary for humans, so you should not worry: all 20 protein amino acids are safely supplied with food, and this amount is enough for a person who leads a normal lifestyle and at least a little watching his diet.
The 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 acids, so professional bodybuilders are forced to take special supplements. With intensive muscle building, 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 an instruction with the content of different AUAs in a dose, which must be read before using the drug.
The effect of peptides on the quality of life of an ordinary person
The need for proteins is present not only among athletes. For example, proteins elastin, keratin, 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, keeping the balance of fat at an optimal level, provide enough 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 with a lack of certain peptides; the maintenance of the psycho-emotional state is carried out, among other things, at the expense of the AMC.
Amino acids and sports
The diet of professional athletes involves perfectly balanced nutrition, which helps maintain muscle tone. They make life very easy, designed specifically for those athletes who work on gaining muscle mass.
As mentioned earlier, amino acids are the main building blocks of proteins needed for muscle growth. They are also able to speed up metabolism and burn fat, which is also important for beautiful muscle relief. When exercising hard, it is necessary to increase the intake of BUAs, since 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 aminocarboxylic 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 with a heavy workload of the day.
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 one BUN, there are a huge number of unpleasant side effects that significantly impair well-being and productivity.
Oversaturation with amino acids can lead to disturbances 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.
In everything you need to know when to stop, so maintaining a healthy lifestyle should not lead to an overabundance of certain “useful” substances in the body. As the classic wrote, "the best is the enemy of the good."
In the article, we examined the formulas and names of all 20 amino acids, the table of the content of the main AMK in products is given above.
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