Complete oxidation of one molecule of glucose yields approximately 30 ATP when cytosolic NADH enters the mitochondria through the glycerol 3 phosphate shuttle, but 32 ATP through the malate aspartate shuttle. The lower yield with the glycerol phosphate shuttle is because:

• A It consumes one ATP per cycle to regenerate dihydroxyacetone phosphate
• B It converts part of the pyruvate pool to lactate before oxidation
• C It bypasses Complex III, losing the Q cycle contribution
• D Its cytosolic reducing equivalents reach the respiratory chain as FADH2, entering at ubiquinone and yielding 1.5 ATP per pair ✓

Explanation

In the glycerol phosphate shuttle, cytosolic NADH reduces dihydroxyacetone phosphate to glycerol 3 phosphate, and the inner membrane flavoprotein glycerol 3 phosphate dehydrogenase reoxidises it, transferring electrons to ubiquinone via FAD. Electrons therefore skip Complex I, so only about 1.5 ATP per NADH pair are produced instead of 2.5, a loss of roughly 1 ATP per cytosolic NADH. The shuttle itself costs no ATP, and Complex III participation is unchanged.

Reference: Lehninger Principles of Biochemistry (Nelson and Cox), 7th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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