Cell Biology MCAT Practice Question
A 3-year-old boy presents with progressive muscle weakness, developmental delay, and recurrent lactic acidosis episodes. His parents report normal early development until age 18 months. Physical examination reveals generalized hypotonia and hepatomegaly. Serum lactate is elevated at 8 mmol/L (normal <2). Brain MRI shows basal ganglia abnormalities. Muscle biopsy demonstrates ragged-red fibers. Biochemical analysis shows normal citric acid cycle intermediate concentrations and intact cristae formation, but the patient has severely impaired NADH reoxidation in isolated mitochondria. Oxygen is available and consumed at low rates despite high NADH levels. Which of the following mitochondrial proteins is most likely defective in this patient?
Answer choices
- APyruvate dehydrogenase complex
- BCarnitine palmitoyltransferase I
- CATP synthase (complex V)
- DCytochrome c oxidase (complex IV)Correct answer
- EUbiquinol-cytochrome c oxidoreductase (complex III)
- FNADH dehydrogenase (complex I)
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