At how many places in Krebs cycle , FADH2 is / are formed ?

Options

A. 1
B. 2
C. 3
D. 4

Answer

To determine how many times FADH2 is formed in the Krebs cycle, we can analyze the steps of the cycle systematically.

### Step-by-Step Solution:

1. **Understanding the Krebs Cycle**: The Krebs cycle, also known as the citric acid cycle or tricarboxylic acid (TCA) cycle, is a series of chemical reactions used by all aerobic organisms to generate energy.

2. **Identifying Key Steps**: The cycle begins with the condensation of acetyl-CoA and oxaloacetate to form citrate. The cycle then progresses through a series of transformations, including decarboxylation and oxidation.

3. **Analyzing Each Step**:
- **Step 1**: Acetyl-CoA combines with oxaloacetate to form citrate.
- **Step 2**: Citrate is converted to isocitrate.
- **Step 3**: Isocitrate undergoes oxidative decarboxylation to form alpha-ketoglutarate, producing NADH.
- **Step 4**: Alpha-ketoglutarate undergoes another oxidative decarboxylation to form succinyl-CoA, producing another NADH.
- **Step 5**: Succinyl-CoA is converted to succinate, generating GTP (or ATP).
- **Step 6**: Succinate is oxidized to fumarate, and this is the step where FADH2 is produced.
- **Step 7**: Fumarate is hydrated to form malate.
- **Step 8**: Malate is oxidized to regenerate oxaloacetate, producing another NADH.

4. **Counting FADH2 Production**: From the analysis, we see that FADH2 is produced only in **Step 6** when succinate is converted to fumarate.

5. **Conclusion**: Therefore, FADH2 is formed at **one place** in the Krebs cycle.

### Final Answer:
FADH2 is formed at **one place** in the Krebs cycle.

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