Niacin is synthesized from-

Ans, is 'c' i.e., Tryptophan Niacin (vitamin B3)o Niacin is a general name for the nicotinic acid and nicotinamide, either of which may act as a source of vitamin in the diet. Nicotinic acid can be formed in the body from tryptophan (1 mg of the vitamin is formed from 60 mg of tryptophan). Therefore, deficiency of tryptophan causes deficiency of niacin.o Niacin, in the form of nicotinamide, is incorporated into the structure of two coenzymes : nicotinamide adenine dinucleotide (NAD+) and nicotinamide adenine dinucleotide phosphate (NADP+). These coenzymes are involved in following reactions :1) Oxidoredution reactions : Both NAD+ and NADP+ participate in many oxidoreduction reactions by acting as coenzymes for various dehydrogenases :NAD+ -linked dehydrogenasesPyruvate dehydrogenase, isocitrate dehydrogenase, malate dehydro-genase, a-ketoglutarate dehydrogenase, glutamate dehydrogenase, glyceraldehyde-3-P dehydrogenase, lactate dehydrogenase, b-hydroxy acyl CoA dehydrogenase, glycerol 3-P dehydrogenase (cytoplasmic).NADP+-linked dehydrogenases Glucose-6-P dehydrogenase, 6-Phosphogluconate dehydrogenase, 3-ketoacyI reductase, Enoyl reductase.2) ADP ribosylation : NAD' functions as ADP-ribose donor for the ADP-ribosylation of protein and poly ADP-ribosylation of nucleoproteins involved in the DNA repair mechanism.