Amino acids are mostly synthesized from a-ketogluaric acid. These are the precursors of amino acids. A five carbon compound formed during Krebs' cycle is a a-ketoglutaric acid which is the first diearboxylic acid formed. Pyruvic acid converted into alanine, a-ketoglutaric acid into glutamic acid, OAA into aspartic acid, polymerization of such amino acids results into formation of proteins.