Q.40 Match the following enzymes with their regulatory mechanism
(a) Phosphofructokinase 1. Product inhibition
(b) Glycogen synthase 2. Control of enzyme synthesis
(c) β-galactosidase 3. Allosteric interaction
(d) Lactate dehydrogenase 4. Covalent modification
(A) (a)-3, (b)-2, (c)-1, (d)-4
(B) (a)-3, (b)-4, (c)-2, (d)-1
(C) (a)-4, (b)-3, (c)-1, (d)-4
(D) (a)-4, (b)-1, (c)-2, (d)-3
Enzyme Regulation Matching: Phosphofructokinase, Glycogen Synthase, β-Galactosidase, Lactate Dehydrogenase
Cells tightly control enzyme activity through mechanisms like allosteric changes, covalent modifications, and gene-level synthesis. The correct matching for this question aligns each enzyme with its primary regulation type. Option (B) provides the accurate pairings.
Correct Answer
B: (a)-3, (b)-4, (c)-2, (d)-1. Phosphofructokinase uses allosteric regulation, glycogen synthase covalent modification, β-galactosidase enzyme synthesis control, and lactate dehydrogenase product inhibition.
Key Mechanisms
Allosteric interaction involves effectors binding non-active sites to alter shape. Covalent modification adds/removes groups like phosphate via kinases/phosphatases. Product inhibition occurs when products block the enzyme. Control of synthesis regulates gene expression for enzyme levels.
Enzyme Details
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Phosphofructokinase (a): Allosteric (3). Inhibited by ATP, activated by AMP in glycolysis.
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Glycogen synthase (b): Covalent (4). Phosphorylated (inactive) by kinases; dephosphorylated (active) by phosphatases.
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β-galactosidase (c): Synthesis control (2). Lac operon induction by lactose boosts transcription.
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Lactate dehydrogenase (d): Product inhibition (1). NADH competes at active site.
Option Analysis
| Option | Matchings | Correctness | Reason |
|---|---|---|---|
| (A) | a-3, b-2, c-1, d-4 | Wrong | Glycogen synthase not synthesis-controlled; covalent key. β-galactosidase not product-inhibited. |
| (B) | a-3, b-4, c-2, d-1 | Correct | Matches textbook mechanisms: allosteric glycolysis control, phosphorylation storage, operon induction, NADH feedback . |
| (C) | a-4, b-3, c-1, d-4 | Wrong | Phosphofructokinase primarily allosteric, not covalent. Duplicate d-4 invalid. |
| (D) | a-4, b-1, c-2, d-3 | Wrong | LDH not allosteric; glycogen synthase not product-inhibited. |
Exam Tips
Recall glycolysis enzymes favor allostery for rapid response. Storage enzymes like glycogen synthase use phosphorylation. Inducible enzymes like β-galactosidase tie to gene regulation. Practice with pathways: feedback often product-based.
