The structure of amino acids. Determination and classification of amino acids

Among a huge variety of natural substances, amino acids occupy a special place. It is explained by their exceptional importance both in biology and in organic chemistry. The fact is that of amino acids are molecules of simple and complex proteins, which are the basis of all forms of life on Earth without exception. It is for this reason that science pays serious attention to the study of such issues as the structure of amino acids, their properties, production and application. The importance of these compounds is also great in medicine, where they are used as therapeutic drugs. For those people who are seriously engaged in their own health and lead an active way of life, protein monomers are a form of food (so-called sports nutrition). Some of their types are used in the chemistry of organic synthesis as a raw material in the production of synthetic fibers - enanth and kapron. As we see, aminocarboxylic acids play a very important role both in nature and in the life of human society, so we will get acquainted with them in more detail.

Features of the structure of amino acids

Compounds of this class belong to amphoteric organic substances, that is, they contain two functional groups, and, therefore, exhibit dual properties. In particular, hydrocarbon radicals are attached to the molecules, which are connected to the amino groups NH ₂ and carboxyl groups COOH. In chemical reactions with other substances, amino acids act as bases, then as acids. The isomerism of such compounds is manifested due to a change or spatial configuration of the carbon skeleton, or the position of the amino group, and the classification of amino acids is determined based on the structural features and properties of the hydrocarbon radical. It can be in the form of an unbranched or branched chain, and also contain cyclic structures.

Optical activity of aminocarboxylic acids

All monomers of polypeptides, and their 20 species, present in the organisms of plants, animals and humans, are L-amino acids. Most of them contain an asymmetric carbon atom, rotating during rotation a polarized beam of light to the left. Two monomers: isoleucine and threonine - have two such carbon atoms, and aminoacetic acid (glycine) - none. The classification of amino acids by optical activity is widely used in biochemistry and molecular biology when studying the translation process in protein biosynthesis. Interestingly, D-forms of amino acids are never included in the composition of polypeptide chains of proteins, but are present in bacterial membranes and in metabolic products of actinomycete fungi, that is, in fact, they are found in natural antibiotics, for example, in gramicidin. In biochemistry, substances with the D-form of spatial structure, such as citrulline, homoserine, ornithine, which play an important role in the reactions of cellular metabolism, are widely known.

What are zwitter ions?

Let us recall once again that protein monomers have functional groups of amines and carboxylic acids in their composition. The particles -NH ₂ and COOH interact among themselves inside the molecule, which leads to the appearance of an internal salt, called the bipolar ion (zwitterion ion). Such an internal structure of amino acids explains their high ability to interact with polar solvents, for example, with water. The presence in solutions of charged particles causes their electrical conductivity.

What are α-amino acids

If the amine group is located in the molecule at the first carbon atom, counting from the location of the carboxyl, such an amino acid is referred to as the α-amino acid class. They occupy a leading place in the classification, because it is from these monomers that all biologically active protein molecules are constructed, for example such as enzymes, hemoglobin, actin, collagen, etc. The structure of amino acids of this class can be considered in the example of glycine, Which is widely used in neurological practice, as a sedative in the treatment of mild forms of depression and neurasthenia.

The international name of this amino acid is α-aminoacetic, it has an optical L-form and is proteinogenic, that is, it participates in the translation process and is part of protein macromolecules.

The role of proteins and their monomers in metabolism

It is impossible to imagine the normal life activity of the mammalian organism, including man, without hormones consisting of protein molecules. The chemical structure of the amino acids included in their composition confirms their belonging to α-forms. For example, triiodothyronine and thyroxine are produced by the thyroid gland. They regulate metabolism and are synthesized in its cells from the α-amino acid of tyrosine. In simple and complex proteins there are both 20 basic monomers and their derivatives. In prothrombin, which regulates blood clotting, carboxyglutamic acid is present, in myosin (muscle protein), methylisin is detected, in the peroxidase enzyme - selenocysteine.

Nutritional value of proteins and their monomers

Considering the structure of amino acids and their classification, we will dwell on a gradation based on the ability or impossibility of protein monomers to be synthesized in cells. Alanine, proline, tyrosine and other compounds are formed in the reactions of plastic metabolism, and tryptophan and seven other amino acids must enter our organism only with food products.

One of the indicators of a correct and balanced diet is the level of human consumption of protein foods. It should be at least a quarter of the total amount of food that has been ingested in a day. It is especially important that proteins contain in their composition valine, isoleucine and other essential amino acids. In this case, the proteins will be called full. They enter the human body from plant foods or products containing mushrooms.

The same irreplaceable monomers of proteins can not be synthesized in mammalian cells. If we consider the structure of amino acid molecules, which are irreplaceable, we can see that they belong to different classes. Thus, valine and leucine belong to the aliphatic series, tryptophan to aromatic amino acids, and threonine to hydroxyamino acids.