Structure and classification of amino acids

As the material basis of all life, protein plays many roles in life activities, such as material transport, biochemical reaction catalysis, metabolic activity regulation and so on Amino acids are the basic components of proteins, and their importance is self-evident In recent years, with the in-depth study of human health and the progress of material separation, purification and identification technology, the physiological function of polypeptide between amino acid monomer and macromolecular protein has attracted more and more scientific attention In fact, to understand the concept of peptide, we should start with its basic component, amino acid   Structure and classification of amino acids In short, a class of organic compounds containing both amino and carboxyl groups can be called amino acids But biological proteins are composed of 20 kinds of common amino acids and a few rare amino acids (such as 4-hydroxyproline, 5-hydroxylysine) The 20 common amino acids that make up a protein are all composed of an amino group, a carboxyl group, a hydrogen atom and a variable R group side chain connected to an α carbon atom The general structural formula is shown in Figure 1-1 It should be noted that all of the 20 amino acids are L-type amino acids (proline is L-type sub amino acid), except glycine (Glycine R group is hydrogen atom) For the classification of amino acids, it can be divided into essential amino acids and non essential amino acids from the perspective of nutrition Essential amino acids refer to the amino acids that can not be synthesized or synthesized too slowly to meet the needs of the body and must be supplemented directly from food Therefore, the long-term lack of essential amino acids in diet will affect health The non essential amino acids refer to the amino acids that can be synthesized by human body and do not depend on the direct supply of food In particular, infants cannot synthesize histidine on their own, so they need one more amino acid (histidine) than adults From the point of view of physical and chemical properties, according to the different side chain properties of R-group on amino acids, amino acids can be generally divided into four categories: R-group is nonpolar (hydrophobic), R-group is polar and uncharged, R-group is polar and negatively charged and positively charged amino acids.