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.

Amino acid supplementation
Various amino acid supplements are available, either as individual amino acids, or in a number of combinations. The most popular amino acid supplements are arginine, tryptophan, tyrosine, glutamine, and lysine.