This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: vitamins, Subject name: Biochemistry
Vitamin synthesised from amino acid is 
Select and explain. 
A. Thiamine, B. Ribolflavin, C. Biotin, D. Niacin
D: Niacin
Answer: D: Niacin 
Explanation: Vitamin synthesized from amino acid niacin.Niacin, or nicotinic acid, is a substituted pyridine derivative. The biologically active coenzyme forms are nicotinamide adenine dinucleotide (NAD+) and its phosphorylated derivative, nicotinamide adenine dinucleotide phosphate.Reference: Lippincott Textbook of Biochemistry, fifth edition, pg no. 379