Proteinogenic amino acids are the 20 amino acids that are found in proteins and used by living organisms to synthesize proteins. These include Alanine, Arginine, Asparagine, Aspartic acid, Cysteine, Glutamic acid, Glutamine, Glycine, Histidine, Isoleucine, Leucine, Lysine, Methionine (start codon), Phenylalanine, Proline, Serine, Threonine, Tryptophan Tyrosine and Valine.