MCAT Biochemistry Question 121: Answer and Explanation
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Question: 121
1. A man collapses while running a marathon and is taken to the emergency room. His blood is found to be somewhat acidic, and further tests show increased lactate dehydrogenase activity. This enzyme is involved in which of the following pathways?
- A. Anaerobic glycolysis
- B. β-Oxidation of fatty acids
- C. Citric acid cycle
- D. Pentose phosphate pathway
Correct Answer: A
Explanation:
Under normal conditions, when oxygen is readily available, the pyruvate generated in glycolysis enters the mitochondrion and is converted into acetyl-CoA by the action of pyruvate dehydrogenase. During strenuous exercise, particularly by individuals in poor physical condition, the oxygen demands of the skeletal muscle may exceed the ability of the heart and lungs to provide oxygen. In this setting, the muscles switch to anaerobic glycolysis, and the pyruvate that is produced is converted to lactate by the action of lactate dehydrogenase.