Difficulty: Easy
Correct Answer: Lactate dehydrogenase
Explanation:
Introduction / Context:
When oxygen is limited, many tissues (e.g., exercising muscle, red blood cells) regenerate NAD+ by reducing pyruvate to lactate. Identifying the correct enzyme ensures conceptual clarity between fermentative pathways and mitochondrial oxidative metabolism.
Given Data / Assumptions:
Concept / Approach:
Lactate dehydrogenase (LDH) catalyzes pyruvate + NADH + H+ → lactate + NAD+. This reaction is reversible and central to the Cori cycle (lactate back to glucose in liver). Other listed enzymes act in unrelated steps or organisms (e.g., pyruvate decarboxylase to acetaldehyde in yeast alcoholic fermentation).
Step-by-Step Solution:
Verification / Alternative check:
Clinical marker: serum LDH rises with tissue damage; lactate accumulation during hypoxia confirms pathway activity.
Why Other Options Are Wrong:
Common Pitfalls:
Mixing up human lactic fermentation with yeast alcoholic fermentation; confusing LDH with pyruvate dehydrogenase.
Final Answer:
Lactate dehydrogenase
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