Two pairs of electrons passing from NADH molecules to oxygen generate

Options

A. (a) 3 ATP
B. (b) 4 ATP
C. (c) 6 ATP
D. (d) 2 ATP

Answer

To solve the question "Two pairs of electrons passing from NADH molecules to oxygen generate," we will break down the process step by step.

### Step-by-Step Solution:

1. **Understanding NADH and its Role**:
- NADH is a key electron carrier in cellular respiration. It is generated during the Krebs cycle and carries electrons to the electron transport chain (ETC).

2. **Electron Transport Chain (ETC)**:
- The ETC is located in the inner mitochondrial membrane and consists of a series of protein complexes (Complex I to IV) and ATP synthase.
- When NADH donates its electrons to the ETC, it undergoes oxidation, releasing energy.

3. **Proton Pumping**:
- Each NADH molecule donates one pair of electrons to the ETC.
- For each pair of electrons transferred from NADH, 3 protons (H⁺ ions) are pumped from the mitochondrial matrix into the intermembrane space.

4. **Calculating for Two Pairs of Electrons**:
- Since the question mentions "two pairs of electrons," this implies two NADH molecules.
- Therefore, 2 NADH will pump out a total of \(2 \times 3 = 6\) protons into the intermembrane space.

5. **ATP Generation**:
- The protons that have been pumped into the intermembrane space create a proton gradient.
- These protons flow back into the mitochondrial matrix through ATP synthase, which uses the energy from this flow to convert ADP and inorganic phosphate into ATP.
- Each proton that flows back through ATP synthase generates one molecule of ATP.

6. **Final Calculation**:
- Since 6 protons are pumped out and then flow back through ATP synthase, this results in the production of 6 ATP molecules.
- Therefore, the answer to the question is that two pairs of electrons passing from NADH molecules to oxygen generate **6 ATP**.

### Final Answer:
**6 ATP**

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