Oxidative phosphorylation is

Options

A. Formation of ATP by transfer of phosphate group from a substrate to ADP
B. Oxidation of phosphate group in ATP
C. Addition of phosphate group to ATP
D. Formation of ATP by energy released from electrons removed during substrate oxidation

Answer

**Step-by-Step Solution:**

1. **Understanding Oxidative Phosphorylation**:
- Oxidative phosphorylation is a metabolic process that occurs in the mitochondria of cells. It involves the formation of ATP (adenosine triphosphate) through the transfer of electrons from NADH and FADH2 to oxygen via the electron transport chain (ETC).

2. **Role of Oxygen**:
- In oxidative phosphorylation, oxygen acts as the final electron acceptor. This means that it combines with electrons and protons (H+ ions) to form water, which is a byproduct of this process.

3. **Distinguishing from Substrate-Level Phosphorylation**:
- It is important to differentiate oxidative phosphorylation from substrate-level phosphorylation. In substrate-level phosphorylation, ATP is formed directly by transferring a phosphate group from a substrate to ADP, without the involvement of oxygen.

4. **Analyzing the Options**:
- **Option 1**: Formation of ATP by transfer of phosphate group from a substrate to ADP - This describes substrate-level phosphorylation, not oxidative phosphorylation.
- **Option 2**: Oxidation of phosphate group in ATP - This is incorrect as ATP already contains three phosphate groups and does not involve oxidation in this context.
- **Option 3**: Addition of phosphate group to ATP - This does not describe oxidative phosphorylation.
- **Option 4**: Formation of ATP by energy released from electrons removed during substrate oxidation - This accurately describes oxidative phosphorylation, as it involves the transfer of electrons through the ETC and the subsequent formation of ATP.

5. **Conclusion**:
- The correct answer to the question "Oxidative phosphorylation is" is **Option 4**: formation of ATP by energy released from electrons removed during substrate oxidation.

---