Approximately how many net ATP are produced via the oxidative energy system from the metabolism of one molecule?

Approximately how many net ATP are produced via the oxidative energy system from the metabolism of one molecule?

• A. 27
• B. 34
• C. 38
• D. 41

Answer: (C)

In aerobic metabolism, the energy yield from oxidizing one molecule of glucose comes from both oxidative phosphorylation and substrate-level phosphorylation, across glycolysis, pyruvate dehydrogenase (PDH) step, and the TCA cycle. Using common teaching approximations, each NADH that donates electrons to the chain yields about 3 ATP and each FADH2 about 2 ATP in the oxidative steps. Glucose oxidation produces 10 NADH total (2 from glycolysis, 2 from PDH, and 6 from the TCA) and 2 FADH2 (from the TCA), plus 2 GTP (substrate-level) from the TCA cycle, with glycolysis contributing 2 ATP substrate-level ATP as well. The oxidative phosphorylation contribution is (10 × 3) + (2 × 2) = 34 ATP. Adding the 4 ATP from substrate-level phosphorylation (2 from glycolysis and 2 from GTP in the TCA) gives about 38 ATP per glucose. While newer models using 2.5 ATP per NADH and 1.5 ATP per FADH2 yield around 32 ATP, 38 ATP is a commonly cited approximate total in many exam contexts, hence the chosen value.

In aerobic metabolism, the energy yield from oxidizing one molecule of glucose comes from both oxidative phosphorylation and substrate-level phosphorylation, across glycolysis, pyruvate dehydrogenase (PDH) step, and the TCA cycle. Using common teaching approximations, each NADH that donates electrons to the chain yields about 3 ATP and each FADH2 about 2 ATP in the oxidative steps. Glucose oxidation produces 10 NADH total (2 from glycolysis, 2 from PDH, and 6 from the TCA) and 2 FADH2 (from the TCA), plus 2 GTP (substrate-level) from the TCA cycle, with glycolysis contributing 2 ATP substrate-level ATP as well. The oxidative phosphorylation contribution is (10 × 3) + (2 × 2) = 34 ATP. Adding the 4 ATP from substrate-level phosphorylation (2 from glycolysis and 2 from GTP in the TCA) gives about 38 ATP per glucose. While newer models using 2.5 ATP per NADH and 1.5 ATP per FADH2 yield around 32 ATP, 38 ATP is a commonly cited approximate total in many exam contexts, hence the chosen value.