Terminal cytochrome of respiratory chain which donates electrons to oxygen is

Options

A. cyt-b
B. cyt-c
C. `cyt-a_(1)`
D. `cyt-a_(3)`

Explanation

To answer the question regarding the terminal cytochrome of the respiratory chain that donates electrons to oxygen, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Electron Transport Chain (ETC)**:
- The electron transport chain is a series of protein complexes located in the inner mitochondrial membrane. It is responsible for the transfer of electrons derived from NADH and FADH2, which are produced during the Krebs cycle.

2. **Identifying the Components of the ETC**:
- The ETC consists of several complexes:
- Complex I: NADH dehydrogenase (NAD complex)
- Complex II: Succinate dehydrogenase (FAD complex)
- Complex III: Ubiquinone-cytochrome c reductase (BC1 complex)
- Complex IV: Cytochrome c oxidase (AA3 complex)

3. **Electron Flow in the ETC**:
- Electrons flow from NADH (Complex I) to ubiquinone (Complex II), then to Complex III, and finally to Complex IV.
- During this process, protons (H+) are pumped across the mitochondrial membrane, creating a proton gradient.

4. **Identifying the Terminal Cytochrome**:
- The terminal cytochrome in the electron transport chain is Complex IV, also known as cytochrome c oxidase (AA3 complex).
- This complex is responsible for transferring electrons to molecular oxygen (O2), which is the final electron acceptor in the chain.

5. **Formation of Water**:
- When electrons are transferred to oxygen, they combine with protons (H+) to form water (H2O), which is a byproduct of cellular respiration.

6. **Conclusion**:
- Therefore, the terminal cytochrome of the respiratory chain that donates electrons to oxygen is **cytochrome c oxidase (Complex IV)**.

### Final Answer:
The terminal cytochrome of the respiratory chain which donates electrons to oxygen is **cytochrome c oxidase (Complex IV)**.

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