This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Amino Acid Metabolism, Subject name: Biochemistry
Melatonin is derived from- 
Select and explain. 
A. Tyrosine, B. Phenylalanine, C. Alanine, D. Tryptophan
D: Tryptophan
Answer: D: Tryptophan 
Explanation: Ans. is 'd' i.e., Tryptophan o Tryptophan is a precursor for synthesis of niacin (nicotinic acid), serotonin and melatonin.Amino acidsBiological important compoundTyrosineCatecholamines (epinephrine, norepinephrine, dopamine), thyroxine, triiodothryonine, melanin.(Note: - Phenylalanine is the precursor of tyrosine, thus it can also give rise to all these compounds through tyrosine (phenylalanine - Tyrosine - Catecholamines thyroxine, T3, melanin).TryptophanVitamin niacin, melatonin, SerotoninGlycineArginineMethionineCreatineGlycine, cysteineBile saltsGlycineHemeAspartic acid and glutaminePyrimidine basesGlycine, aspartic acid, glutaminePurine basesb-alanineCoenzyme-AArginineNitric oxideHistidine, Arginine, lysineKeratinMethionine, lysineCarnitineGABAGlutamateGlutamate, cysteine, glycineGlutathione