Question

25. What is the total number of ATP that can be generated from one molecule of glucose?

Answer 1

Short answer:
- Classical textbook answer: 36 ATP per glucose in eukaryotic cells (38 ATP is the theoretical maximum in prokaryotes).
- More accurate modern estimate: about 30–32 ATP per glucose (depends on P/O ratios, proton leak and shuttle systems).

Why the different numbers (brief breakdown, classical values using NADH → 3 ATP and FADH2 → 2 ATP):
- Glycolysis: net 2 ATP + 2 NADH
- Pyruvate → acetyl‑CoA (2 pyruvates): 2 NADH
- TCA cycle (2 acetyl‑CoA): 6 NADH + 2 FADH2 + 2 ATP (GTP)
Totals: 10 NADH, 2 FADH2, 4 ATP (substrate‑level). Using 3 ATP/NADH and 2 ATP/FADH2 → 10×3 + 2×2 + 4 = 38 ATP (prokaryotes). In eukaryotes, cytosolic NADH from glycolysis may be shuttled (glycerol‑3‑phosphate shuttle gives FADH2 equivalents), lowering the yield to ~36 ATP. Using modern P/O ratios (NADH ≈ 2.5, FADH2 ≈ 1.5) gives ≈32 ATP (often reported as ~30–32 ATP after accounting for leaks and transport costs).