The citric acid cycle itself doesn't directly produce a large amount of ATP; its primary contribution to ATP production comes indirectly through the electron transport chain and oxidative phosphorylation.
While the citric acid cycle directly produces only 1 ATP (or GTP, which is readily converted to ATP) per cycle, its significance lies in generating high-energy electron carriers, NADH and FADH2. These carriers then fuel the electron transport chain, leading to substantial ATP production.
Here's a breakdown of the ATP yield, considering the indirect contribution:
-
Direct ATP: 1 ATP (or GTP) per cycle.
-
Indirect ATP (via NADH and FADH2):
- Each NADH produced in the citric acid cycle yields approximately 2.5 ATP molecules in oxidative phosphorylation (as per the reference).
- Each FADH2 produced yields approximately 1.5 ATP molecules (as per the reference).
To calculate the total ATP generated indirectly from one turn of the cycle:
| Molecule | Quantity Produced per Cycle | ATP Yield per Molecule | Total ATP Contribution |
|---|---|---|---|
| NADH | 3 | 2.5 | 7.5 |
| FADH2 | 1 | 1.5 | 1.5 |
| Total Indirect ATP | 9 |
Therefore, the total ATP produced both directly and indirectly per cycle is approximately 1 + 9 = 10 ATP. It's important to note that this is an estimate, as the exact yield can vary depending on cellular conditions. The actual yield from NADH and FADH2 can range from 1.5 to 2.5 ATP and 1.5 to 2.5 ATP respectively, so the number of ATP molecules produced from one glucose molecule during cellular respiration has a range from 30 to 38 ATP.
