The sequence of cytochromes is

Options

A. Cyt, a, b, c, `a_(3)`
B. Cyt, b, c, a, `a_(3)`
C. Cyt b, a, `a_(3)`, c
D. Cyt b, c, `a_(3)`, a

Answer

To determine the correct sequence of cytochromes in the electron transport chain (ETC), we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Electron Transport Chain (ETC)**:
- The ETC is a series of protein complexes located in the inner mitochondrial membrane that transfer electrons from electron donors to electron acceptors via redox reactions.

2. **Identify the Complexes**:
- The main complexes involved in the ETC are:
- **Complex I**: NADH dehydrogenase (NADH hydrogenase)
- **Complex II**: FADH2
- **Complex III**: Cytochrome bc1 complex
- **Complex IV**: Cytochrome c oxidase

3. **Determine the Sequence of Cytochromes**:
- Electrons flow from Complex I to Complex II, then to Complex III, and finally to Complex IV.
- Within Complex III, the cytochromes involved are cytochrome b and cytochrome c.
- In Complex IV, the cytochromes involved are cytochrome a and cytochrome a3.

4. **Compile the Sequence**:
- The correct sequence of cytochromes based on the flow of electrons is:
- **Cytochrome b** → **Cytochrome c** → **Cytochrome a** → **Cytochrome a3**.

5. **Match with Given Options**:
- The options provided were:
- A) cytochrome a b c3
- B) cytochrome b c a a3
- C) cytochrome a a3 c b
- D) cytochrome b c a3 a
- The correct sequence matches with option B: **cytochrome b c a a3**.

### Final Answer:
The correct sequence of cytochromes is **cytochrome b c a a3**.

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