an organic acid containing the amino group NH2 and a carboxyl group, esp any of the amino acids that are the chief components of proteins and are synthesized by living cells or are obtained as essential components of the diet
Amino acids possess both an acidic (COO-) and a basic (NH2+) group. Each of the 20 naturally occurring amino acids can exist in two optically isomeric forms, only one of which, (-), is found in living organisms. Combined in long chains by linking the NH2+ of one with the terminal CH group of a second (peptide bonds) they constitute proteins — Professor Steven Rose