amino acid

n. A large group of chemical compounds containing both an amino group, NH2, and a carboxyl group, COOH, about 20 of which form all the proteins and peptides which make up living tissue in all living things on Earth. Some amino acids such as glutamate, glycine, and tyrosine are synthesized in the body, and some, called essential amino acids, such as lysine, tryptophan, and phenylalanine, have to be gleaned from the environment, usually in the diet.