This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Miscellaneous (Bio-Chemistry), Subject name: Biochemistry
Serotonin is a derivative of 
Select and explain. 
A. Tryptophan, B. Tyrosine, C. Phenylalanine, D. Melatonin
A: Tryptophan
Answer: A: Tryptophan 
Explanation: (A) Tryptophan # SEROTONIN (5-hydroxytryptamine, 5 HT), produced from tryptophan is important in mere impulse transmission (neurotransmitter)> It regulates sleep, behaviour, blood pressure etc.> Hydroxylation of tryptophan to 5-hydroxytryptophan is catalyzed by liver tyrosine hydroxylase.> Subsequent decarboxylation forms serotonin (5-hydroxytryptamine), a potent vasoconstrictor and stimulator of smooth muscle contraction.> Catabolism of serotonin is initiated by monoamine oxidase (MAO) catalyzed oxidative deamination to 5-hydroxindoleacetate, which humans excrete in their urine (2-8 mg/d)> The psychic stimulation that follows administration of iproniazid is attributed to its ability to prolong the action monoamine oxidase> Serotonin or 5-hydroxytryptamine (5 HT) is a neurotransmitter, synthesized from tryptophan.> Normally, about 1 % of tryptophan is converted to serotonin> The production of 5HT occurs in the target tissues.