<prompt> which of the following is a essential amino acid ?LysineAlanineAsparagineGlycine  <response>: Essential amino acids are tryptophan valine threonine leucine lysine phenylalanine methionine-total 8amino acids TV TILL 8 PM. their carbon skeleton cannot be synthesized by human beings so preformed amino acid are to be taken in food for normal growth. Normal growth will not occur if one such amino acid is deficient in the diet. Ref: DM Vasudevan - Textbook of Biochemistry for Medical Students, 7th edition, page no: 27 