Q31. The non–coenzyme vitamin is ________
(A) Ascorbic acid
(B) Folic acid
(C) Nicotinic acid
(D) Thiamine
Ascorbic acid is the non-coenzyme vitamin among the options. Unlike the B vitamins listed, it primarily functions as an antioxidant and cofactor rather than forming a classic coenzyme.
Option Analysis
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(A) Ascorbic acid (Vitamin C): Acts as a cofactor for enzymes like prolyl hydroxylase in collagen synthesis but does not form a coenzyme like NAD or TPP. It supports redox reactions directly as an antioxidant.
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(B) Folic acid (Vitamin B9): Converts to tetrahydrofolate (THF), a coenzyme for one-carbon transfers in DNA synthesis and methionine metabolism.
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(C) Nicotinic acid (Vitamin B3): Precursor to NAD+ and NADP+, essential coenzymes in redox reactions like glycolysis and the citric acid cycle.
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(D) Thiamine (Vitamin B1): Forms thiamine pyrophosphate (TPP), a coenzyme for decarboxylation in pyruvate dehydrogenase and transketolase reactions.
Correct Answer
(A) Ascorbic acid serves as the non-coenzyme vitamin, distinguishing it from the coenzyme-forming B vitamins in competitive exams like CSIR NET Life Sciences.
The non-coenzyme vitamin among Ascorbic acid, Folic acid, Nicotinic acid, and Thiamine is a key concept in biochemistry for CSIR NET Life Sciences aspirants. Understanding which vitamin does not form a classic coenzyme helps differentiate water-soluble vitamins’ roles in metabolism.
Vitamin Functions
Water-soluble vitamins like the B-complex often derive coenzymes for enzymatic reactions, but Ascorbic acid stands out. It acts as a cofactor and antioxidant without forming structures like NAD or TPP. B vitamins support energy metabolism through coenzymes.
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Folic acid enables THF for nucleotide synthesis.
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Nicotinic acid powers NAD in oxidation-reduction.
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Thiamine drives TPP in decarboxylation pathways.
Exam Relevance
In CSIR NET, questions test coenzyme precursors versus non-coenzyme roles. Ascorbic acid’s distinction arises because it reduces iron or maintains enzyme activity directly, not as a bound coenzyme. Deficiency links to scurvy, unlike beriberi (Thiamine) or pellagra (Nicotinic acid).
Study Tips
Review coenzyme pathways: TPP for pyruvate dehydrogenase, THF for purine synthesis, NAD for dehydrogenases. Practice MCQs distinguishing cofactors from coenzymes.
