This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Endocrinology, Subject name: Biochemistry
Melatonin is derived from 
Select and explain. 
A. Tyrosine, B. Tryptophan, C. Glutathione, D. None
B: Tryptophan
Answer: B: Tryptophan 
Explanation: Tryptophan is first hydroxylated by tryptophan Hydroxylase 5-hydroxytryptophan is decarboxylated to serotoninSerotonin is acetylated Fuher methylated with the help of S adenosylmethionine (SAM)Ref: DM Vasudevan, 7th edition, page no: 241, fig 18.10