In TCA cycle, substrate level phosphorylation takes place during the conversion of

Options

A. oxaloacetic acid to citric acid
B. succinyl CoA to succinic acid
C. succinic acid to fumaric acid
D. furnaric acid to malic acid

Answer

To solve the question regarding substrate level phosphorylation in the TCA cycle, we need to identify the specific conversion where ATP is produced directly from ADP and inorganic phosphate (Pi).

### Step-by-Step Solution:

1. **Understanding the TCA Cycle**: The TCA cycle, also known as the Krebs cycle, is a series of enzymatic reactions that take place in the mitochondria. It is crucial for energy production in aerobic respiration.

2. **Identifying Substrate Level Phosphorylation**: Substrate level phosphorylation refers to the direct synthesis of ATP from ADP and a phosphorylated substrate. In the TCA cycle, this occurs during a specific conversion.

3. **Analyzing the Options**:
- **Option 1: Oxaloacetic acid to citric acid**: This reaction involves the condensation of acetyl-CoA with oxaloacetate to form citric acid. No ATP is produced here.
- **Option 2: Succinyl-CoA to succinic acid**: This conversion is where substrate level phosphorylation occurs. Succinyl-CoA is converted to succinate, and during this process, GTP (which can be readily converted to ATP) is produced. This is the key step we are looking for.
- **Option 3: Succinic acid to fumaric acid**: This reaction involves the oxidation of succinate to fumarate, producing FADH2, but no ATP is produced.
- **Option 4: Fumaric acid to malic acid**: This step involves the addition of water to fumarate to form malate, with no ATP production.

4. **Conclusion**: The correct answer is the conversion of **succinyl-CoA to succinic acid**, as this is the step in the TCA cycle where substrate level phosphorylation occurs, resulting in the formation of GTP (or ATP).

### Final Answer:
Substrate level phosphorylation in the TCA cycle takes place during the conversion of **succinyl-CoA to succinic acid**.