During oxidative phosphorylation, protons return to

Options

A. (a) matrix from outside
B. (b) outside from matrix
C. (c) in both directions
D. (d) mitochondria to cytoplasm

Answer

**Step-by-Step Solution:**

1. **Understanding Oxidative Phosphorylation**:
- Oxidative phosphorylation is a metabolic pathway that uses oxygen and the electron transport chain to produce ATP. It occurs in the inner mitochondrial membrane.

2. **Electron Transport Chain (ETC)**:
- The process begins with the electron transport chain, where electrons are transferred through a series of protein complexes. This transfer of electrons is essential for creating a proton gradient.

3. **Proton Gradient Formation**:
- As electrons move through the complexes of the electron transport chain, protons (H⁺ ions) are pumped from the mitochondrial matrix into the intermembrane space. This creates a higher concentration of protons outside the matrix compared to inside.

4. **Role of ATP Synthase**:
- The protons that have accumulated in the intermembrane space flow back into the mitochondrial matrix through a protein complex known as ATP synthase. This flow of protons is driven by the concentration gradient.

5. **ATP Production**:
- As protons return to the matrix, ATP synthase utilizes the energy from this movement to convert ADP and inorganic phosphate (Pi) into ATP. This process is known as phosphorylation.

6. **Conclusion**:
- Therefore, during oxidative phosphorylation, protons return to the mitochondrial matrix from the intermembrane space. The correct answer to the question is "matrix".

**Final Answer**: Protons return to the matrix during oxidative phosphorylation.

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