In a TCA cycle, how many `NADH_2` and `FADH_2` are produced, respectively?

Options

A. `3 NADH_2, 1 FADH_2`
B. `2 NADH_2, 1 FADH_2`
C. `4 NADH_2, 1 FADH_2`
D. `4 NADH_2, 2 FADH_2`

Answer

To determine the number of NADH2 and FADH2 produced in the TCA cycle, we will analyze the steps involved in the cycle:

### Step-by-Step Solution:

1. **Understanding the TCA Cycle**: The TCA cycle, also known as the Krebs cycle or citric acid cycle, is a series of biochemical reactions used by all aerobic organisms to generate energy through the oxidation of acetate derived from carbohydrates, fats, and proteins.

2. **Identifying the Key Steps**:
- The cycle begins with the combination of acetyl-CoA and oxaloacetate to form citrate.
- Citrate is then converted into isocitrate.
- Isocitrate is oxidized to alpha-ketoglutarate, during which NAD+ is reduced to NADH2 (1 NADH2 produced).
- Alpha-ketoglutarate is then converted to succinyl-CoA, producing another NADH2 (2 NADH2 produced).
- Succinyl-CoA is converted to succinate, and this step does not produce NADH2 but produces GTP or ATP.
- Succinate is then converted to fumarate, during which FAD is reduced to FADH2 (1 FADH2 produced).
- Fumarate is converted to malate.
- Finally, malate is oxidized back to oxaloacetate, producing another NADH2 (3 NADH2 produced in total).

3. **Counting the Products**:
- From the steps analyzed:
- NADH2 produced: 3 (from isocitrate to alpha-ketoglutarate, alpha-ketoglutarate to succinyl-CoA, and malate to oxaloacetate)
- FADH2 produced: 1 (from succinate to fumarate)

4. **Final Count**:
- Therefore, the total production in one cycle of the TCA cycle is:
- **NADH2**: 3
- **FADH2**: 1

### Conclusion:
The answer to the question is that in one complete turn of the TCA cycle, **3 NADH2** and **1 FADH2** are produced.

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