Ubiquinone receives reducing equivalents from

Options

A. `NAD^(+)`
B. `FADH_(2)`
C. `NADH+H^(+)`
D. Both (2) & (3)

Answer

To answer the question "Ubiquinone receives reducing equivalents from," we will break down the process step by step.

### Step-by-Step Solution:

1. **Understanding Ubiquinone**:
- Ubiquinone, also known as coenzyme Q, is a vital component of the electron transport chain in cellular respiration. It plays a crucial role in transferring electrons between different complexes.

2. **Identifying the Complexes**:
- Ubiquinone is associated with two main complexes in the electron transport chain:
- **Complex I (NADH dehydrogenase)**
- **Complex II (Succinate dehydrogenase)**

3. **Source of Reducing Equivalents from Complex I**:
- Complex I receives electrons from NADH.
- The reaction involves NADH being oxidized to NAD⁺, releasing electrons that are transferred to ubiquinone.
- This process also releases protons (H⁺) into the intermembrane space.

4. **Source of Reducing Equivalents from Complex II**:
- Complex II receives electrons from FADH₂ (flavin adenine dinucleotide).
- In this case, FADH₂ is oxidized to FAD, and the electrons are transferred to ubiquinone.
- This also results in the release of protons.

5. **Conclusion**:
- Therefore, ubiquinone receives reducing equivalents from both NADH (through Complex I) and FADH₂ (through Complex II).
- The correct answer to the question is that ubiquinone receives reducing equivalents from both sources: NADH and FADH₂.

### Final Answer:
Ubiquinone receives reducing equivalents from NADH and FADH₂.