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
The following metabolite is a derivative of tryptophan- 
Select and explain. 
A. Melatonin, B. Thyroxine, C. Epinephrine, D. Nor epinephrine
A: Melatonin
Answer: A: Melatonin 
Explanation: Ans. is 'a' i.e., Melatonin Amino acidsBiological important compoundTyrosineCatecholamines (epinephrineQ, norepinephrineQ, dopamineQ), thyroxineQ, triiodothryonine, melanin Q.(Note: - Phenylalanine is the precursor of tyrosine, thus it can also give rise to all these compounds through tyrosine (phenylalanine - TyrosineQ - CatecholaminesQ, thyroxineQ, T3, melaninQ).TryptophanVitamin niacinQ, melatoninQ, SerotoninQGlycineQ,ArginineQ,methionineQCreatineQGlycine, cysteineBile saltsGlycineHeme.Aspartic acid andglutaminePyrimidine basesGlycineQ,aspartic acid,glutaminePurine basesQb-alanineCoenzyme-AArginineNitric oxideQGlutamateGama-amino butyric acid (GABA)