Cytoplasmic NADH generated during glycolysis must be reoxidized via shuttle systems. In adult human brain and fast-twitch skeletal muscle, the shuttle in operation delivers these electrons to which ETC component?
- A The FAD-linked mitochondrial glycerol-3-phosphate dehydrogenase, yielding about 1.5 ATP ✓
- B The FMN of Complex I, yielding about 2.5 ATP
- C Ubiquinone directly via ETF dehydrogenase, yielding about 1.5 ATP
- D Cytochrome c, bypassing Complexes III and IV
Correct answer: A. The FAD-linked mitochondrial glycerol-3-phosphate dehydrogenase, yielding about 1.5 ATP
Explanation
Brain and skeletal muscle rely mainly on the glycerol-3-phosphate shuttle: cytosolic NADH reduces DHAP to glycerol-3-phosphate, whose electrons enter mitochondria through the FAD-dependent inner membrane glycerol-3-phosphate dehydrogenase, feeding ubiquinone as FADH2 and yielding roughly 1.5 ATP. Liver, heart and kidney instead use the malate-aspartate shuttle, which preserves the NADH equivalence and gives about 2.5 ATP.
Reference: Harper's Illustrated Biochemistry, 32nd ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.