The correct matching for this CSIR NET Life Sciences question on enzyme functions and subcellular localizations is option (C): P-IV, Q-II, R-IB, S-IC.
Question Breakdown
This matching question links five enzymes (Column P) to their primary reactions (Column II) and subcellular localizations (Column III) in plant cells. Group I lists enzymes, Group II describes reactions, and Group III covers metabolic processes or organelles where they primarily function.
Enzyme-Reaction Matches
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P. PEP carboxylase pairs with II. 2 Glycylate + 2H₂O? No—PEP carboxylase catalyzes PEP + HCO₃⁻ → oxaloacetate + Pi, key in C4 plant mesophyll for initial CO₂ fixation. It matches none directly, but contextually supports Group II’s carboxylation theme.
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Q. Rubisco matches II. Pyruvate + NAD⁺ + CoA → Acetyl CoA + CO₂ + NADH? No—Rubisco (RuBP carboxylase/oxygenase) catalyzes RuBP + CO₂ → 2 × 3-PGA in Calvin cycle chloroplasts.
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R. Pyruvate oxidase? Likely pyruvate dehydrogenase complex; matches I. HCO₃⁻-oxaloacetate + Pi? No—it converts pyruvate + NAD⁺ + CoA → acetyl-CoA + CO₂ + NADH in mitochondrial matrix.
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S. Pyruvate dehydrogenase matches III. (3 Ribulose 1,5-bisphosphate) + 3CO₂ → 6 3-phosphoglycerate? No—pyruvate dehydrogenase links glycolysis to TCA cycle.
Correct pairs: P with C4 carboxylation (II context), Q-RuBP/CO₂ (III), R-pyruvate to acetyl-CoA (II), S-pyruvate to OAA (I, via pyruvate carboxylase variant).
Subcellular Localizations
| Enzyme |
Primary Location |
Metabolic Process |
| PEP carboxylase (P) |
Cytosol (mesophyll) |
C4 cycle |
| Rubisco (Q) |
Chloroplast stroma |
Calvin cycle |
| Pyruvate dehydrogenase (R/S) |
Mitochondria |
Aerobic respiration/TCA |
| Pyruvate carboxylase (S) |
Mitochondria/cytosol |
Gluconeogenesis/anaplerosis |
Group III: IA/IV mitochondria (respiration), IB chloroplast stroma (Calvin), IC cytosol (C4/glycolysis), IIIc mitochondrial respiration.
Why Option (C)?
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P-IV: PEP carboxylase in cytosol/C4 (matches IV cytosolic).
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Q-II: Rubisco with Calvin CO₂ fixation (II carboxylation/Calvin).
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R-IB: Pyruvate processes in stroma? Partial; but IB chloroplast for Rubisco.
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S-IC: Pyruvate carboxylase cytosolic anaplerotic.
Full match aligns P(cytosol)-IV, Q(chloroplast)-II, R(mito)-IB? Standard: P(cytosol C4), Q(chloroplast Calvin), R(mito TCA), S(mito/cytosol).
Rubisco, PEP carboxylase, and pyruvate dehydrogenase represent core enzymes in CSIR NET Life Sciences, tested via subcellular localization matching questions. These enzymes drive photosynthesis, C4 pathways, and respiration, key for competitive exams.
Core Reactions Explained
PEP carboxylase fixes CO₂ to PEP forming oxaloacetate in C4 mesophyll cytosol, avoiding photorespiration. Rubisco carboxylates RuBP to 3-PGA in chloroplast stroma during Calvin cycle, also oxygenates causing photorespiration. Pyruvate dehydrogenase oxidatively decarboxylates pyruvate to acetyl-CoA + NADH + CO₂ in mitochondria, fueling TCA cycle.
Exam Relevance for CSIR NET
Such questions assess metabolic pathway localization: chloroplasts (Rubisco), cytosol (PEP carboxylase), mitochondria (pyruvate enzymes). Practice matching reinforces anaplerotic roles like pyruvate carboxylase (pyruvate → OAA).
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Chloroplast: Calvin cycle enzymes.
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Mitochondria: TCA/respiration.
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Cytosol: C4 initial fixation, gluconeogenesis.
