Amino acids are molecules that (in technical terms) contain a basic amino (-NH2) group, an acidic carboxyl (-COOH) group and a side chain attached to an end carbon atom. The 20 essential amino acids (not made by the body and thus required to be present in the diet) are alanine, arginine, asparagine, aspartic acid, cysteine, glutamic acid, glutamine, glycine, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, proline, serine, threonine, tryptophan, tyrosine, and valine.