Among the 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 amino acids are composed of molecules of simple and complex proteins, which are the basis of all life forms 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 use. The importance of these compounds in medicine, where they are used as therapeutic drugs. For those people who are seriously engaged in their own health and lead an active lifestyle, protein monomers are a form of food (the so-called sports nutrition). Some of their types are used in organic chemistry as a raw material in the production of synthetic fibers - enanth and nylon. As you can see, aminocarboxylic acids play a very important role both in nature and in the life of human society, so we will get to know 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 connected to the amino groups of NH 2 and the carboxyl groups of COOH are present in the composition of the molecules. In chemical reactions with other substances, amino acids act either as bases or as acids. The isomerism of such compounds is manifested due to a change in either the spatial configuration of the carbon skeleton or the position of the amino group, and the classification of amino acids is determined based on structural features and properties of the hydrocarbon radical. It can take the form of a straight or branched chain, and also contain cyclic structures.
The optical activity of aminocarboxylic acids
All monomers of polypeptides, and their 20 species present in plants, animals, and humans, are L-amino acids. Most of them contain an asymmetric carbon atom, which rotates a polarized light beam to the left during rotation. Two monomers: isoleucine and threonine - have two such carbon atoms, and aminoacetic acid (glycine) - not one. The classification of amino acids by optical activity is widely used in biochemistry and molecular biology in the study of the translation process in protein biosynthesis. It is interesting that the D-forms of amino acids are never part of the polypeptide chains of proteins, but are present in bacterial membranes and in metabolic products of actinomycetes, that is, in fact, they are found in natural antibiotics, for example, gramicidin. In biochemistry, substances with a D-form of a spatial structure are widely known, such as citrulline, homoserin, ornithine, which play an important role in cellular metabolism reactions.
What are zwitterions?
We recall once again that protein monomers incorporate functional groups of amines and carboxylic acids. Particles -NH 2 and COOH interact with each other inside the molecule, which leads to the appearance of an internal salt called a bipolar ion (zwitterion). This internal structure of amino acids explains their high ability to interact with polar solvents, such as water. The presence of charged particles in solutions determines 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, this amino acid belongs to the class of α-amino acids. They occupy a leading place in the classification, because it is from these monomers that all biologically active protein molecules are built, for example, such as enzymes, hemoglobin, actin, collagen, etc. The structure of the amino acids of this class can be examined by the example of glycine, the same which is widely used in neurological practice, as a sedative in the treatment of mild forms of depression and neurasthenia.
The international name for this amino acid is α-aminoacetic, it has an optical L-shape 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 functioning of the organism of mammals, including humans, without hormones consisting of protein molecules. The chemical structure of the amino acids that make up their composition confirms their belonging to α-forms. For example, triiodothyronine and thyroxine are produced by the thyroid gland. They regulate the metabolism and are synthesized in its cells from the α – amino acid tyrosine. Simple and complex proteins contain both 20 basic monomers and their derivatives. Carboxyglutamic acid is present in prothrombin, which regulates blood coagulation, methylisine is found in myosin (muscle protein), and selenocysteine is found in the peroxidase enzyme.
The nutritional value of proteins and their monomers
Considering the structure of amino acids and their classification, let us dwell on the gradation based on the ability or inability of protein monomers to be synthesized in cells. Alanine, proline, tyrosine and other compounds are formed in plastic exchange reactions, and tryptophan and seven other amino acids should enter our body only with food.
One of the indicators of proper and balanced nutrition is the level of human consumption of protein foods. It should be at least a quarter of the total amount of food received in the body per day. It is especially important that proteins contain valine, isoleucine, and other essential amino acids. In this case, the proteins will be called complete. They enter the human body from plant foods or products containing mushrooms.
Irreplaceable protein monomers themselves cannot be synthesized in mammalian cells. If we consider the structure of amino acid molecules, which are indispensable, you can make sure that they belong to different classes. So, valine and leucine belong to the aliphatic series, tryptophan - to aromatic amino acids, and threonine - to hydroxy amino acids .