What is the maximum theoretical ATP yield per glucose molecule in aerobic metabolism?

• A. 2
• B. 36
• C. 4
• D. 38

Answer: (B)

In aerobic metabolism, glucose is fully oxidized so most energy comes from oxidative phosphorylation driven by NADH and FADH2 produced along the pathway. The best-case breakdown gives a large total: glycolysis directly provides 2 ATP and makes 2 NADH; if these NADH enter the mitochondria efficiently (via a shuttle like malate–aspartate), they can contribute about 6 ATP. That puts glycolysis up to around 8 ATP. Pyruvate oxidation yields 2 NADH, adding about 6 ATP. The citric acid cycle, for the two acetyl-CoA produced from one glucose, generates 6 NADH (18 ATP), 2 FADH2 (3 ATP), and 2 GTP (2 ATP), totaling 23 ATP. Summing these gives about 37 ATP in the most favorable case. In practice, small losses from transporting molecules across membranes and rounding of numbers typically bring the commonly cited maximum to 36 ATP per glucose. So 36 ATP is the standard upper bound used in many contexts, reflecting the best-case efficiency while acknowledging transport and rounding factors. Real cellular yields are usually lower due to inefficiencies and leaks, often around 30–32 ATP.