Biosynthesis of amino acids:

Microorganisms and Plants can synthesize all of the 20 standard amino acids. Mammals, moreover, cannot synthesize all 20 and must acquire some of them in their diet.  Those  amino  acids  which  are  supplied  in  the  diet  are  referred  to  as essential,  while  the remainder  which can be synthesized  through the organism  are termed nonessential.  This designation refers to the required 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, therefore the essential ones are Leu, His, Ile, Thr, Lys, Met, Phe, Trp and Val for the structures of the 20 standard amino acids. The ways for the biosynthesis of amino acids are diverse and frequently vary from one organism to another.  Though,  they  all have  an important  feature  in general:  their  carbon  skeletons  come  from  key intermediates  in middle metabolic pathways. The amino acids can be grouped together into six biosynthetic pathways depending on the intermediate from that they are derived. the main amino group commonly comes from transamination of glutamate.