Metabolic Pathways and Regulation · USMLE Step 1

Which three enzymes catalyze the essentially irreversible, regulatory steps of glycolysis?

  1. Hexokinase, PFK-1, Pyruvate kinase
  2. Glucokinase, Aldolase, Enolase
  3. Phosphoglycerate kinase, Triose phosphate isomerase, Lactate dehydrogenase
  4. Glucose-6-phosphatase, Pyruvate carboxylase, PEPCK
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Correct answer: Hexokinase, PFK-1, Pyruvate kinase

The irreversible, regulatory steps in glycolysis are catalyzed by hexokinase (or glucokinase), PFK-1, and pyruvate kinase — these steps have large negative ΔG and allow control of glycolytic flux.

Difficulty: Medium Question 4 of 19

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