Microorganisms and Plants can synthesize all of the 20 standard amino acids. Mammals, furthermore, cannot synthesize all 20 and must obtain some of them in their diet. Those amino acids which are supplied in the diet are referred to as essential, whereas the remainder which can be synthesized by the organism are termed nonessential. This designation refers to the needed of an organism under a particular group of conditions. In the humans nonessential amino acids are Arg, Gly, Asn, Ala, Cys, Asp, Pro, Glu, Gln, Ser and Tyr, thus the essential ones are Leu, His, Ile, Thr, Lys, Met, Phe, Trp and Val for the structures of the 20 standard amino acids.