Select the correct sequence of formation of given intermediates of Krebs' cycle.

Options

A. succinate `rarr` Malate `rarr` Fumarate `rarr OA A`
B. Fumarate `rarr` Succinate `rarr` Malate `rarr OA A`
C. Succinate `rarr` Fumarate `rarr` Malate `rarr OA A`
D. Malate `rarr` Fumarate `rarr` Succinate `rarr OA A`

Answer

To determine the correct sequence of formation of the intermediates in the Krebs cycle, we will analyze the process step by step.

### Step-by-Step Solution:

1. **Identify the Intermediates**: The intermediates given are succinate, fumarate, malate, and oxaloacetic acid.

2. **Starting Point**: The Krebs cycle begins with succinate. This is the first intermediate we will consider.

3. **Conversion of Succinate to Fumarate**:
- The first reaction involves the conversion of succinate into fumarate.
- This reaction is catalyzed by the enzyme **succinate dehydrogenase**.
- During this process, succinate loses hydrogen (dehydrogenation) and is transformed into fumarate.

4. **Conversion of Fumarate to Malate**:
- The next step is the conversion of fumarate into malate.
- This reaction is a hydration reaction, meaning it involves the addition of water.
- The enzyme responsible for this conversion is **fumarase**.
- Fumarate gains a water molecule to become malate.

5. **Conversion of Malate to Oxaloacetic Acid**:
- The final step involves the conversion of malate into oxaloacetic acid (or oxaloacetate).
- This is another dehydrogenation reaction, where malate loses hydrogen to form oxaloacetic acid.
- The enzyme that catalyzes this reaction is **malate dehydrogenase**.

6. **Final Sequence**:
- Thus, the correct sequence of formation of the intermediates in the Krebs cycle is:
- **Succinate → Fumarate → Malate → Oxaloacetic Acid**.

### Conclusion:
The correct answer is the sequence: **Succinate, Fumarate, Malate, Oxaloacetic Acid**.

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