Metabolic Pathways and Regulation · USMLE Step 1

Which of these is a catabolic pathway that generates reducing equivalents (NADH, FADH2) and feeds electrons into the electron transport chain?

  1. Glycolysis in the cytosol
  2. Pentose phosphate pathway
  3. Urea cycle in the liver
  4. Citric acid cycle (TCA cycle)
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Correct answer: Citric acid cycle (TCA cycle)

The citric acid cycle oxidizes acetyl-CoA to CO₂ and in the process produces NADH and FADH₂, which serve as electron donors for the electron transport chain and thereby drive ATP production.

Difficulty: Medium Question 15 of 19

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