Cytosolic NADH generated by glyceraldehyde-3-phosphate dehydrogenase during glycolysis in skeletal muscle yields approximately 1.5 ATP on reoxidation rather than 2.5. What accounts for this lower yield?
- A Skeletal muscle lacks any shuttle for cytosolic NADH
- B Half of the cytosolic NADH is consumed by lactate dehydrogenase
- C The glycerol-3-phosphate shuttle transfers electrons to FAD on the outer face of the inner membrane ✓
- D Complex I pumps fewer protons when fed from cytosolic NADH
Correct answer: C. The glycerol-3-phosphate shuttle transfers electrons to FAD on the outer face of the inner membrane
Explanation
Muscle and brain use the glycerol-3-phosphate shuttle: cytosolic glycerol-3-phosphate dehydrogenase reduces DHAP using NADH, and the mitochondrial isoform, facing the intermembrane space, reoxidizes it with FAD. Electrons then enter at coenzyme Q, bypassing Complex I, giving about 1.5 ATP. Heart and liver instead use the malate-aspartate shuttle, preserving the NADH yield of about 2.5 ATP.
Reference: Marks' Basic Medical Biochemistry, 6th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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