Substrate level phosphorylation does not occur in which of the following reaction of aerobic respiration ?

Options

A. 1,3-diPGA `to` 3-PGA
B. 3-PGA `to` 2-PGA
C. PEP `to` Pyruvate
D. Succinyl CoA `to` Succinic acid

Answer

To determine in which reaction of aerobic respiration substrate-level phosphorylation does not occur, we need to analyze the reactions involved in glycolysis and the Krebs cycle.

### Step-by-Step Solution:

1. **Understanding Substrate-Level Phosphorylation**:
- Substrate-level phosphorylation is a process where a phosphate group is directly transferred from a substrate molecule to ADP, forming ATP. This occurs in specific steps during glycolysis and the Krebs cycle.

2. **Identifying Key Reactions**:
- In glycolysis, several reactions involve substrate-level phosphorylation:
- Conversion of 1,3-bisphosphoglycerate to 3-phosphoglycerate (ATP is produced).
- Conversion of phosphoenolpyruvate to pyruvate (ATP is produced).
- In the Krebs cycle, substrate-level phosphorylation occurs when succinyl-CoA is converted to succinate, producing ATP.

3. **Analyzing the Options**:
- The question asks which reaction does not involve substrate-level phosphorylation.
- The conversion of 3-phosphoglycerate to 2-phosphoglycerate does not produce ATP, indicating that substrate-level phosphorylation does not occur in this step.

4. **Conclusion**:
- Therefore, the reaction where substrate-level phosphorylation does not occur is the conversion of 3-phosphoglycerate to 2-phosphoglycerate.

### Final Answer:
Substrate-level phosphorylation does not occur in the conversion of 3-phosphoglycerate to 2-phosphoglycerate.

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