One glucose on complete oxidation yields 36 ATP . During this oxidation of glucose , what is the contribution of the Krebs cycle via oxidative phosphorylation ?

Options

A. 11 ATP
B. 12 ATP
C. 22 ATP
D. 24 ATP

Answer

To determine the contribution of the Krebs cycle (also known as the citric acid cycle or TCA cycle) to the total ATP yield during the complete oxidation of one glucose molecule, we can break down the process step by step.

### Step-by-Step Solution:

1. **Understanding the Total ATP Yield**:
- The complete oxidation of one glucose molecule yields a total of 36 ATP.

2. **ATP Yield from Glycolysis**:
- Glycolysis, which occurs in the cytoplasm, produces:
- 2 ATP directly.
- 2 NADH, which can be converted into ATP during oxidative phosphorylation. Each NADH yields approximately 2 ATP, so:
- 2 NADH x 2 ATP/NADH = 4 ATP.
- Therefore, the total ATP from glycolysis is:
- 2 ATP (direct) + 4 ATP (from NADH) = **6 ATP**.

3. **ATP Yield from the Transition Phase**:
- The transition phase occurs between glycolysis and the Krebs cycle, where:
- 2 NADH are produced (from the conversion of pyruvate to acetyl-CoA).
- These 2 NADH also yield ATP during oxidative phosphorylation:
- 2 NADH x 2 ATP/NADH = 4 ATP.
- Thus, the total ATP from the transition phase is:
- **6 ATP** (2 NADH converted to 4 ATP).

4. **ATP Yield from the Krebs Cycle**:
- In the Krebs cycle, the following products are generated from one glucose molecule (which produces 2 acetyl-CoA):
- 6 NADH (3 from each acetyl-CoA).
- 2 FADH2 (1 from each acetyl-CoA).
- The ATP yield from these products is:
- 6 NADH x 2 ATP/NADH = 12 ATP.
- 2 FADH2 x 1.5 ATP/FADH2 = 3 ATP (since each FADH2 yields approximately 1.5 ATP).
- Therefore, the total ATP yield from the Krebs cycle is:
- 12 ATP (from NADH) + 3 ATP (from FADH2) = **15 ATP**.

5. **Total ATP Calculation**:
- Now, we can sum up all the ATP contributions:
- Glycolysis: 6 ATP
- Transition Phase: 6 ATP
- Krebs Cycle: 15 ATP
- Total ATP = 6 + 6 + 15 = **27 ATP**.

6. **Final Contribution of the Krebs Cycle**:
- The total contribution of the Krebs cycle to the overall ATP yield is:
- 15 ATP (from NADH and FADH2 produced in the Krebs cycle).

### Conclusion:
The contribution of the Krebs cycle via oxidative phosphorylation is **15 ATP**.