Apentix/AP Biology/Unit 3: Cellular Energetics/Question
AP Biologymediummcq1 pt

An aerobically grown yeast strain carries a mutation that greatly weakens alpha-ketoglutarate dehydrogenase, one enzyme of the citric acid cycle. Which metabolic consequence is expected?

A.The cycle reverses direction and consumes NADH to manufacture sugar from CO2
B.Cycle flux past alpha-ketoglutarate slows, cutting NADH output and shrinking the electron supply delivered to the respiratory chain
C.Oxaloacetate accumulates without limit because citrate synthase can no longer act
D.ATP yield stays unchanged because substrate level phosphorylation covers aerobic needs

Explanation

Core Concept

Alpha-ketoglutarate dehydrogenase performs one of the cycle's oxidation steps, releasing one carbon as CO2 while reducing one NAD+ per pass. Weakening it creates a bottleneck: upstream intermediates pile up while succinyl-CoA formation drops. Reduced NADH delivery to the electron transport chain means diminished proton pumping and proportionally lower aerobic ATP production. The cell leans on alternate routes such as amino acid metabolism, yet net respiratory yield stays suppressed.

Correct Answer

BCycle flux past alpha-ketoglutarate slows, cutting NADH output and shrinking the electron supply delivered to the respiratory chain

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