Cytoplasmic NADH is oxidatively phosphorylated inside mitochondrion. Mitochondrion is impermeable to NADH. Entry into mitochondrion is effect through

Options

A. Shuttle system
B. Faciliated diffusion
C. Active absorption
D. `F_(0)` tunnel of elementary particles.

Answer

**Step-by-Step Solution:**

1. **Understanding the Problem**: The question states that cytoplasmic NADH is oxidatively phosphorylated inside the mitochondrion, but NADH cannot directly enter the mitochondrion due to its impermeability. We need to identify how NADH enters the mitochondrion.

2. **Identifying the Mechanism**: Since NADH is produced during glycolysis in the cytoplasm and needs to be transported into the mitochondria for the electron transport chain, we need to consider the mechanisms available for this transport.

3. **Considering the Options**:
- **Shuttle System**: This is a known mechanism that helps transport NADH equivalents into the mitochondria.
- **Facilitated Diffusion**: This typically refers to the passive transport of molecules across a membrane via specific transport proteins, but NADH is not able to pass through the mitochondrial membrane this way.
- **Active Absorption**: This refers to the transport of molecules against their concentration gradient, which is not the case for NADH.
- **F0 Tunnel of Elementary Particles**: This option does not relate to the transport of NADH.

4. **Conclusion**: The correct mechanism for the entry of cytoplasmic NADH into the mitochondrion is through the **shuttle system**. This system involves the conversion of NADH to malate, which can then enter the mitochondria, where it is converted back to NADH.

5. **Final Answer**: The entry into the mitochondrion is effected through the **shuttle system**.

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