Which statement about the pyruvate carboxylase reaction of gluconeogenesis is correct?
- A It is a mitochondrial reaction requiring biotin and ATP, and is allosterically activated by acetyl-CoA ✓
- B It is a cytosolic reaction requiring thiamine pyrophosphate and is inhibited by acetyl-CoA
- C It uses NAD+ as cofactor and converts pyruvate directly to phosphoenolpyruvate
- D It is activated by insulin and generates oxaloacetate in the endoplasmic reticulum
Correct answer: A. It is a mitochondrial reaction requiring biotin and ATP, and is allosterically activated by acetyl-CoA
Explanation
Pyruvate carboxylase catalyzes the ATP-dependent, biotin-mediated carboxylation of pyruvate to oxaloacetate inside mitochondria, the first obligatory bypass of pyruvate kinase. Acetyl-CoA, abundant when fatty acids are being oxidized during fasting, allosterically activates the enzyme, signaling ample substrate energy for gluconeogenesis. Conversion of oxaloacetate to phosphoenolpyruvate is performed separately by PEPCK using GTP, so option C conflates two distinct steps. Insulin represses rather than activates gluconeogenic enzymes.
Reference: Lehninger Principles of Biochemistry, 8th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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