How many molecules of ATP are gained by substrate-level phosphorylation from the complete breakdown of a single molecule of glucose in the presence of oxygen?

• A. 2
• B. 3
• C. About 16 ATP
• D. About 32 ATP
• E. 4

Answer: (E)

Verified step by step guidance

1. Begin by understanding the process of cellular respiration, which includes glycolysis, the citric acid cycle, and oxidative phosphorylation.
2. In glycolysis, glucose is broken down into two molecules of pyruvate. During this process, substrate-level phosphorylation occurs, producing a net gain of 2 ATP molecules.
3. Next, consider the citric acid cycle (also known as the Krebs cycle), where each acetyl-CoA molecule contributes to the production of ATP through substrate-level phosphorylation. However, this cycle primarily generates NADH and FADH2 for oxidative phosphorylation.
4. Substrate-level phosphorylation directly produces ATP without the involvement of the electron transport chain. In the complete breakdown of glucose, only glycolysis contributes to ATP production via substrate-level phosphorylation.
5. Therefore, from the complete breakdown of a single molecule of glucose, substrate-level phosphorylation results in a net gain of 2 ATP molecules from glycolysis alone.