This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Proteins and Amino Acids, Subject name: Biochemistry
Melatonin is synthesized from 
Select and explain. 
A. Histidine, B. Methionine, C. Tryptophan, D. Phenylalanine
C: Tryptophan
Answer: C: Tryptophan 
Explanation: Ans. c (Tryptophan). (Ref. Harper, Biochemistry, 25th /pg.355)AMINOACID DERIVATIVESPhenylalanine:# Phenylalanine >> tyrosine >> dopa >> norepinephrine >> epinephrine# Phenylalanine >> tyrosine >> dopa >> dopamine >> melanin2# Phenylalanine >> tyrosine >> thyroxineTryptophan# Niacin# Serotonin# Melatonin2Histidine# Histidine -Histamine (by decarboxylation)Glycine# Porphyrin and haeme# Purines# Creatine (totally madeup of glycine + arginine + methionine; mnemonic--GAM)# Glutathione (totally made up of glycine + cystine+ glutamate; mnemonic--GCG)Arginine# Carnitine# UreaMethionine# Choline