Which of the following organic acid is the substrate for the step in which GTP is formed during Kreb's cycle ?

Options

A. alpha - ketoglutaric acid.
B. Succinyl - Co - A
C. Citrate.
D. Acetyl CoA

Answer

To solve the question of which organic acid serves as the substrate for the step in which GTP is formed during the Krebs cycle, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Krebs Cycle**: The Krebs cycle, also known as the citric acid cycle or TCA cycle, is a series of biochemical reactions that occur in the mitochondria. It plays a crucial role in cellular respiration, where energy is produced.

2. **Identifying the Key Steps**: Within the Krebs cycle, there are several important steps, including the conversion of different substrates into products. One of the key reactions involves the conversion of succinyl-CoA to succinate.

3. **Recognizing GTP Formation**: During the conversion of succinyl-CoA to succinate, energy is released, which is used to form GTP (guanosine triphosphate). This is a critical step in the cycle where substrate-level phosphorylation occurs.

4. **Identifying the Substrate**: From the options provided (α-ketoglutaric acid, succinyl-CoA, citrate, and acetyl-CoA), we need to identify which one is the substrate for the step where GTP is synthesized.

5. **Conclusion**: The correct substrate for the step in which GTP is formed during the Krebs cycle is **succinyl-CoA**. This compound is converted into succinate while producing GTP.

### Final Answer:
The organic acid that serves as the substrate for the step in which GTP is formed during the Krebs cycle is **succinyl-CoA**.

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