aminoAmino acid definition -- An amino acid is any of a group of organic molecules that consists of a basic amino group (-NH2), an acidic carboxyl group (-COOH), and an organic R group (or side chain), which is unique to each amino acid. When two or more amino acids are put together, it is called a peptide.

Organisms differ considerably in their ability to synthesize an amino acid from the intermediates of metabolic pathways. Most vertebrates can form only the chemically most simple amino acids; the others must be supplied in the diet. Humans, for example, synthesize about 10 of the 20 common amino acids; these are termed nonessential amino acids.