Substrate level phosphorylation occurs in TCA cycle during conversion of :

Options

A. Oxaloacetic acid to citric acid
B. Succinyl CoA to succinic acid
C. Succinic acid to fumaric acid
D. Fumaric acid to malic acid

Answer

### 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 (or GTP). This occurs in specific steps of metabolic pathways, including the TCA cycle.

2. **Identifying the TCA Cycle**:
The TCA cycle, also known as the citric acid cycle or Krebs cycle, is a series of chemical reactions used by all aerobic organisms to generate energy through the oxidation of acetyl-CoA derived from carbohydrates, fats, and proteins.

3. **Analyzing the Steps of the TCA Cycle**:
- The cycle begins with the condensation of acetyl-CoA with oxaloacetate to form citric acid.
- Citric acid is then converted to isocitrate.
- Isocitrate undergoes oxidative decarboxylation to form alpha-ketoglutarate.
- Alpha-ketoglutarate is further converted to succinyl-CoA, releasing CO2.
- **Key Step**: The conversion of succinyl-CoA to succinate is crucial because it is here that substrate level phosphorylation occurs, resulting in the formation of GTP (from GDP) and ATP (from ADP).

4. **Conclusion**:
The correct answer to the question is that substrate level phosphorylation occurs during the conversion of **succinyl-CoA to succinic acid** in the TCA cycle.