Q.31 Match the following enzymes in column I with their cofactors in column IIColumn I
(P) Pyruvate decarboxylase
(Q) Glyceraldehyde 3-phosphate dehydrogenase
(R) Pyruvate carboxylase
(S) Glucose-6-phosphate dehydrogenase
Column II
i. Biocytin
ii. NADP+
iii. NAD+
iv. Thiamine pyrophosphate
(A) P-ii; Q-i; R-iv; S-iii
(B) P-iv; Q-iii; R-i; S-ii
(C) P-i; Q-ii; R-iii; S-iv
(D) P-iii; Q-i; R-iv; S-ii
Pyruvate decarboxylase requires thiamine pyrophosphate (TPP, iv), glyceraldehyde 3-phosphate dehydrogenase uses NAD+ (iii), pyruvate carboxylase needs biocytin (i, the biotin-lysine complex), and glucose-6-phosphate dehydrogenase employs NADP+ (ii).
The correct matching is option (B): P-iv, Q-iii, R-i, S-ii.
Enzyme-Cofactor Matches
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(P) Pyruvate decarboxylase → (iv) Thiamine pyrophosphate: This enzyme catalyzes pyruvate to acetaldehyde + CO₂ in fermentation, using TPP to form a carbanion that attacks pyruvate’s carbonyl.
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(Q) Glyceraldehyde 3-phosphate dehydrogenase → (iii) NAD+: In glycolysis, it oxidizes G3P to 1,3-bisphosphoglycerate, reducing NAD+ to NADH via a cysteine hemithioacetal intermediate.
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(R) Pyruvate carboxylase → (i) Biocytin: This biotin-dependent enzyme carboxylates pyruvate to oxaloacetate using biotin covalently bound to lysine (biocytin) as the CO₂ carrier in anaplerosis.
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(Q) Glucose-6-phosphate dehydrogenase → (ii) NADP+: The pentose phosphate pathway’s first enzyme oxidizes G6P to 6-phosphogluconolactone, reducing NADP+ to NADPH for biosynthesis and antioxidant defense.
Option Analysis
Option (A) P-ii; Q-i; R-iv; S-iii: Incorrect. P mismatches with NADP+ (TPP needed); Q with biocytin (NAD+ required); R with TPP (biocytin essential); S with NAD+ (NADP+ specific).
Option (B) P-iv; Q-iii; R-i; S-ii: Correct, as detailed in matches above.
Option (C) P-i; Q-ii; R-iii; S-iv: Incorrect. P with biocytin (TPP); Q with NADP+ (NAD+); R with NAD+ (biocytin); S with TPP (NADP+).
Option (D) P-iii; Q-i; R-iv; S-ii: Incorrect. P with NAD+ (TPP); Q with biocytin (NAD+). R and S partially match but overall wrong.
Pyruvate decarboxylase cofactor, glyceraldehyde 3-phosphate dehydrogenase NAD, pyruvate carboxylase biocytin, and glucose-6-phosphate dehydrogenase NADP+ matching is a key CSIR NET Life Sciences topic testing biochemistry knowledge. This guide solves the exact question with mechanisms.
Cofactor Roles Explained
Thiamine pyrophosphate (TPP) in pyruvate decarboxylase facilitates decarboxylation by stabilizing the enamine intermediate post-pyruvate addition. NAD+ accepts hydride from glyceraldehyde 3-phosphate dehydrogenase’s thiohemiacetal. Biocytin shuttles CO₂ in pyruvate carboxylase’s two-step carboxylation. NADP+ drives NADPH production in glucose-6-phosphate dehydrogenase for redox balance.
CSIR NET Exam Tips
Focus on glycolytic, gluconeogenic, and pentose phosphate enzymes’ cofactors. Mnemonics: TPP for decarboxylases, biotin for carboxylases, NAD(H) for catabolism, NADP(H) for anabolism. Practice similar match-the-following for quick scoring.
