Cytosolic NADH generated during aerobic glycolysis must be shuttled into mitochondria for oxidative phosphorylation. Compared with skeletal muscle, the liver uses a shuttle that delivers electrons to complex I rather than complex II of the respiratory chain. How many ATP equivalents are produced per cytosolic NADH by the hepatic shuttle?
- A 1.5
- B 2.0
- C 2.5 ✓
- D 3.0
Correct answer: C. 2.5
Explanation
The malate-aspartate shuttle, operating mainly in liver, heart, and kidney, transfers reducing equivalents onto mitochondrial NAD+, regenerating NADH inside the matrix. Matrix NADH enters the chain at complex I and pumps protons at complexes I, III, and IV, giving approximately 2.5 ATP. The glycerol 3 phosphate shuttle of muscle and brain hands electrons to FAD at the outer face of complex II, bypassing complex I and yielding only 1.5 ATP, which is the key distractor.
Reference: Lippincott Biochemistry, 8th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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