An essential amino acid, or indispensable amino acid, is an amino acid that cannot be synthesized by the organism, and must be supplied in diet.
The 9 amino acids humans cannot synthesize (F V T W M L I K H):
Animal and plant proteins are made up of about 20 common amino acids.
Synthesis of 6 other amino acids - conditionally essential - can be limited under special conditions (R C G Q P Y): arginine, cysteine, glycine, glutamine, proline, and tyrosine.
Dispensable amino acids can be synthesized in the human body, 5 (A D N E S): alanine, aspartic acid, asparagine, glutamic acid and serine .