In mitochondrial electron transport system, for every two pairs of electrons that pass from NADH molecules through a sequential series of cytochrome enzymes to molecular oxygen generate :

Options

A. 3 ATP
B. 4 ATP
C. 6 ATP
D. 2 ATP

Answer

To solve the question regarding the mitochondrial electron transport system and the ATP generation from NADH, we can break it down into the following steps:

### Step-by-Step Solution:

1. **Understanding the Electron Transport Chain (ETC)**:
- The electron transport chain is a series of protein complexes and other molecules that transfer electrons from electron donors like NADH to electron acceptors such as oxygen.
- NADH donates electrons to the chain, which are passed through various cytochrome enzymes.

2. **Electrons from NADH**:
- Each NADH molecule donates a pair of electrons to the electron transport chain.
- For every pair of electrons transferred from NADH, a certain amount of ATP is synthesized.

3. **ATP Yield from NADH**:
- It is known that for every pair of electrons transferred from NADH, approximately 3 ATP molecules are produced.
- This is due to the proton gradient generated across the mitochondrial membrane, which drives ATP synthesis.

4. **Calculating ATP from Two Pairs of Electrons**:
- Since the question states "for every two pairs of electrons," we need to calculate the total ATP produced from these two pairs.
- Each pair of electrons generates 3 ATP, so for two pairs of electrons:
\[ \text{Total ATP} = 2 \text{ pairs} \times 3 \text{ ATP/pair} = 6 \text{ ATP} \]

5. **Final Answer**:
- Therefore, the total number of ATP molecules generated from two pairs of electrons that pass from NADH through the electron transport chain to molecular oxygen is **6 ATP**.