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 solve the question regarding the production of NADH2 and FADH2 in the TCA cycle, we can break down the process step by step:

### Step-by-Step Solution:

1. **Understanding the TCA Cycle**:
- The TCA cycle, also known as the tricarboxylic acid cycle or citric acid cycle, is a series of biochemical reactions that takes place in the mitochondria of cells. It consists of 8 steps involving various types of reactions including redox, hydration, dehydration, and decarboxylation.

2. **Identifying Key Reactions**:
- In the TCA cycle, certain key reactions lead to the production of NADH and FADH2:
- When isocitrate is converted to alpha-ketoglutarate, one NADH molecule is produced.
- When alpha-ketoglutarate is converted to succinyl-CoA, another NADH molecule is produced.
- When succinate is converted to fumarate, one FADH2 molecule is produced.
- When malate is converted to oxaloacetate, one more NADH molecule is produced.

3. **Counting the Molecules**:
- From the above reactions, we can summarize the production:
- **NADH**:
- 1 from isocitrate to alpha-ketoglutarate
- 1 from alpha-ketoglutarate to succinyl-CoA
- 1 from malate to oxaloacetate
- Total NADH produced = 3
- **FADH2**:
- 1 from succinate to fumarate
- Total FADH2 produced = 1

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

### Final Answer:
In a TCA cycle, the number of NADH2 and FADH2 produced respectively is **3 NADH2 and 1 FADH2**.