Which is not an essential amino acid?

Ans: d (Cystein) Ref: Vasydevan, 4th ed, p. 5th ed, p. 191; Harper, p. 28Essential amino acids:PhenylalanineLeucineLysineValineIsoleucineThreonineMethionineTryptophanSemi essential amino acids:ArginineHistidineAmino acids with basic side chain:(or positively charged amino acids)Arginine - most basic amino acidLysineHistidineAmino acids with acidic side chain:(or negatively charged amino acids)Aspartate / AspargineGlutamate / Glutamine Amino acids with side chain containing sulphur:CysteineMethionineAmino acids producing hypoglycaemia:Leucine by increasing insulin secretionArginineAmino acids with aromatic side chain:i) Phenyl alanineii) Tyrosineiii) Tryptophaniv) HistidineAmino acids with aliphatic side chain:GlycineAlanineValineLeucineIsoleucineIminoacid:ProlineSelenocysteineNOTE: 21st amino acid--selenocysteine