Which statement best describes ATP yield from glucose oxidation through glycolysis, PDH, and TCA, considering shuttle variability?

Which statement best describes ATP yield from glucose oxidation through glycolysis, PDH, and TCA, considering shuttle variability?

• A. Total yield is about 26 ATP.
• B. Total yield is about 28–30 ATP.
• C. Total yield is about 30–32 ATP.
• D. Total yield is about 34–36 ATP.

Answer: (C)

Shuttle-dependent transfer of cytosolic NADH into mitochondria determines the total ATP yield from glucose oxidation. Glycolysis provides 2 ATP net and generates 2 NADH in the cytosol. To use those NADH for oxidative phosphorylation, they must be shuttled into mitochondria. If the malate–aspartate shuttle is used, those 2 NADH effectively contribute about 5 ATP. If the glycerol-3-phosphate shuttle is used, they contribute about 3 ATP. Pyruvate from glycolysis is converted to acetyl-CoA by the pyruvate dehydrogenase complex in the mitochondria, yielding 2 NADH (one per pyruvate), which give about 5 ATP. The two acetyl-CoA enter the TCA cycle, giving each turn: 3 NADH (9 per acetyl-CoA, so 18 total), 1 FADH2 (3 per acetyl-CoA, so 6 total), and 1 GTP (2 ATP per glucose). Altogether per glucose that’s about 20 ATP from the TCA and its immediate outputs. Putting it together: - With the malate–aspartate shuttle: 2 ATP (glycolysis) + 5 (NADH from glycolysis) + 5 (PDH) + 20 (TCA) = roughly 32 ATP. - With the glycerol-3-phosphate shuttle: 2 ATP + 3 + 5 + 20 = roughly 30 ATP. Thus the total yield is about 30–32 ATP, depending on the shuttle used.

Shuttle-dependent transfer of cytosolic NADH into mitochondria determines the total ATP yield from glucose oxidation.

Glycolysis provides 2 ATP net and generates 2 NADH in the cytosol. To use those NADH for oxidative phosphorylation, they must be shuttled into mitochondria. If the malate–aspartate shuttle is used, those 2 NADH effectively contribute about 5 ATP. If the glycerol-3-phosphate shuttle is used, they contribute about 3 ATP.

Pyruvate from glycolysis is converted to acetyl-CoA by the pyruvate dehydrogenase complex in the mitochondria, yielding 2 NADH (one per pyruvate), which give about 5 ATP.

The two acetyl-CoA enter the TCA cycle, giving each turn: 3 NADH (9 per acetyl-CoA, so 18 total), 1 FADH2 (3 per acetyl-CoA, so 6 total), and 1 GTP (2 ATP per glucose). Altogether per glucose that’s about 20 ATP from the TCA and its immediate outputs.

Putting it together:

• With the malate–aspartate shuttle: 2 ATP (glycolysis) + 5 (NADH from glycolysis) + 5 (PDH) + 20 (TCA) = roughly 32 ATP.

• With the glycerol-3-phosphate shuttle: 2 ATP + 3 + 5 + 20 = roughly 30 ATP.

Thus the total yield is about 30–32 ATP, depending on the shuttle used.