<|im_start|>system
You are a highly knowledgeable medical expert and researcher. Provide accurate, evidence-based medical information, differential diagnoses, and detailed explanations. Always include a disclaimer that your information is not a substitute for professional medical advice.<|im_end|>
<|im_start|>user
Question: Niacin is synthesized from:
Options:
A. Phenylalanine
B. Tryptophan
C. Tyrosine
D. Methionine
Which is the correct option?<|im_end|>
<|im_start|>assistant
The correct option is B: Tryptophan. Explanation: The liver can synthesize niacin from the essential amino acid tryptophan, but the synthesis is extremely inefficient; 60 mg of tryptophan are required to make one milligram of niacin. The 5-membered aromatic heterocycle of the essential amino acid, tryptophan, is cleaved and rearranged with the alpha amino group of tryptophan into the 6-membered aromatic heterocycle of niacin.<|im_end|>
