How many substrate level phosphorylation occur in Kreb's cycle?

Options

A. 2
B. 3
C. 4
D. None

Answer

To determine how many substrate-level phosphorylations occur in the Krebs cycle, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Krebs Cycle**: The Krebs cycle, also known as the tricarboxylic acid (TCA) 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.

2. **Defining 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 process occurs in specific steps of metabolic pathways.

3. **Identifying the Step in the Krebs Cycle**: In the Krebs cycle, substrate-level phosphorylation occurs specifically during the conversion of succinyl-CoA to succinate. In this step, a molecule of GTP (which can be readily converted to ATP) is produced.

4. **Counting the Substrate-Level Phosphorylation Events**: In the Krebs cycle, there is only one step where substrate-level phosphorylation occurs, which is during the conversion of succinyl-CoA to succinate.

5. **Conclusion**: Therefore, the total number of substrate-level phosphorylations that occur in the Krebs cycle is **1**.

### Final Answer:
The number of substrate-level phosphorylations that occur in the Krebs cycle is **1**.

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