Cell Biology MCAT Practice Question
A 45-year-old woman with a history of progressive exercise intolerance and myalgias undergoes muscle biopsy. Electron microscopy reveals abnormal mitochondria with irregular cristae. Isolated mitochondria from the biopsy show reduced ATP production despite adequate oxygen and substrate availability. Measurement of the proton gradient across the inner mitochondrial membrane reveals significant depolarization. When the mitochondria are treated with oligomycin (an ATP synthase inhibitor), the membrane potential partially recovers toward normal levels. Which of the following best explains why oligomycin treatment partially restores the mitochondrial membrane potential?
Answer choices
- DOligomycin prevents proton dissipation through ATP synthase, allowing the electron transport chain to maintain the proton gradient without being short-circuitedCorrect answer
- AOligomycin directly inhibits Complex I of the electron transport chain, preventing futile NADH oxidation that was dissipating the proton gradient
- BATP synthase was hydrolyzing ATP rather than synthesizing it, and oligomycin prevents this reverse reaction from further depolarizing the membrane
- COligomycin blocks uncoupling proteins in the inner mitochondrial membrane, reducing the proton leak responsible for the depolarization
- EOligomycin inhibits the pyruvate transporter, reducing mitochondrial substrate overload that was causing oxidative stress
- FOligomycin stimulates an alternative ATP synthesis pathway through substrate-level phosphorylation in the mitochondrial matrix
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