Amino Acid defined
An alpha-amino acid has the generic formula H2NCHRCOOH, where R is an organic substituent;[1] the amino group is attached to the carbon atom immediately adjacent to the carboxylate group (the α–carbon). Other types of amino acid exist when the amino group is attached to a different carbon atom; for example, in gamma-amino acids (such asgamma-amino-butyric acid) the carbon atom to which the amino group attaches is separated from the carboxylate group by two other carbon atoms. The various alpha-amino acids differ in which side-chain (R-group) is attached to their alpha carbon, and can vary in size from just onehydrogen atom in glycine to a large heterocyclic group in tryptophan.
Amino acids serve as the building blocks of proteins, which are linear chains of amino acids. Amino acids can be linked together in varying sequences to form a vast variety of proteins.[2]
Twenty amino acids are naturally incorporated into polypeptides and are called proteinogenic or standard amino acids. These 20 are encoded by the universal genetic code.
Nine standard amino acids are called "essential" for humans because they cannot be created from other compounds by the human body, and so must be taken in as food.
Amino acids are important in nutrition and are commonly used in nutrition supplements, fertilizers, food technology and industry. In industry, applications include the production of biodegradable plastics, drugs, andchiral catalysts.
When taken up into the human body from the diet, the 22 standard amino acids either are used to synthesize proteins and other biomolecules or are oxidized to urea and carbon dioxide as a source of energy.[31] The oxidation pathway starts with the removal of the amino group by a transaminase, the amino group is then fed into the urea cycle. The other product of transamidation is a keto acid that enters the citric acid cycle.[32]Glucogenic amino acids can also be converted into glucose, through gluconeogenesis.[33]
Pyrrolysine trait is restricted to several microbes, and only one organism has both Pyl and Sec.
Of the 22 standard amino acids, 9 are called essential amino acids because the human body cannot synthesize them from other compounds at the level needed for normal growth, so they must be obtained from food.[34]
In addition, cysteine, taurine, tyrosine, and arginine are semiessential amino-acids in children, because the metabolic pathways that synthesize these amino acids are not fully developed.[35][36] The amounts required also depend on the age and health of the individual, so it is hard to make general statements about the dietary requirement for some amino acids.