In alcoholic fermentation by yeast, which two enzymes sequentially catalyze the conversion of pyruvate into ethanol and carbon dioxide?
Answer and explanation
Correct answer: A. Pyruvate decarboxylase and alcohol dehydrogenase
- Step 1: Under anaerobic conditions, yeast cells ferment pyruvate to regenerate for glycolysis.
- Step 2: In the first step, pyruvate decarboxylase (requiring TPP and ) decarboxylates pyruvate (3C) to acetaldehyde (2C), releasing .
- Step 3: In the second step, alcohol dehydrogenase reduces acetaldehyde to ethanol using NADH, regenerating .
Answer
Pyruvate decarboxylase and alcohol dehydrogenase
Why not the others: 'Lactate dehydrogenase and pyruvate dehydrogenase' catalyze lactic acid fermentation in muscle/bacteria and the aerobic link reaction, respectively; 'Hexokinase and phosphoglucomutase' function in glucose phosphorylation and glycogen/starch mobilization; 'Pyruvate kinase and enolase' are upstream enzymes of glycolysis.
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