29. Approximately how many molecules of ATP are synthesized via cellular respiration for every glucose molecule used? (assume oxygenated environment)

a. 12

b. 24

c. 36

d. 48

Answer: c. 36

Explanation:

Cellular respiration oxidizes food molecules. The chemiosmotic model suggests that one ATP molecule is generated for each proton pump activated by the electron transport chain. Since the electrons from NADH activate three pumps and those from FADH2 activate two, we would expect each molecule of NADH and FADH2 to generate three and two ATP molecules, respectively.

However, because eukaryotic cells carry out glycolysis in their cytoplasm and the Krebs cycle within their mitochondria, they must transport the two molecules of NADH produced during glycolysis across the mitochondrial membranes, which requires one ATP per molecule of NADH. Thus, the net ATP production is decreased by two. Therefore, the overall ATP production resulting from aerobic respiration theoretically should be 4 (from substrate-level phosphorylation during glycolysis) + 30 (3 from each of 10 molecules of NADH) + 4 (2 from each of 2 molecules of FADH2) - 2 (for transport of glycolytic NADH) = 36 molecules of ATP