Amino acids

Amino acids, class of organic acids containing a carboxyl group (COOH) and 1 or more (NH₂) groups. Amino acids are synthesized in cells and are the basis of proteins. Amino acids are white crystalline solids that are soluble in water; they can act as acids or bases depending on the chemical environment. All amino acids (except glycine) contain at least 1 asymmetric carbon atom to which are attached the carboxyl group, the amino group, a hydrogen atom, and a fourth group that differs for each amino acid and determines its character. Amino acids can exist in 2 mirror-image forms. Generally only L-isomers (left-turning) occur in nature, but a few bacteria contain D-isomers (right-turning). Organisms link amino acids in chains called polypeptides and proteins. Digestion breaks down these linkages.

See also: Protein.