Which is correct in view of fluid mosaic model ?

Options

A. Proteins can flip-flop lipids cannot
B. Neither proteins nor lipids can flip-flop
C. Both lipids and proteins can flip-flop
D. Lipids can rarely flip-flop , proteins cannot.

Answer

### Step-by-Step Solution:

1. **Understanding the Fluid Mosaic Model**:
- The fluid mosaic model describes the structure of the cell membrane, which consists of a phospholipid bilayer with embedded proteins. This model was proposed by scientists H. S. J. Singer and G. L. Nicholson in 1972.

2. **Components of the Cell Membrane**:
- The cell membrane is primarily made up of phospholipids and proteins. The phospholipids form a bilayer, with hydrophilic (water-attracting) heads facing outward and hydrophobic (water-repelling) tails facing inward.

3. **Movement of Lipids**:
- According to the fluid mosaic model, lipids can move laterally within the bilayer and can also undergo a process known as "flip-flop," where they can move from one leaflet of the bilayer to the other. However, this flip-flop movement is relatively rare.

4. **Movement of Proteins**:
- Proteins embedded in the lipid bilayer do not flip-flop due to their extensive polar regions, which prevent them from moving between the leaflets of the bilayer. Instead, they can move laterally within the same layer.

5. **Evaluating the Options**:
- **Option 1**: "Proteins can flip-flop, lipids cannot" - Incorrect (proteins cannot flip-flop).
- **Option 2**: "Neither proteins nor lipids can flip-flop" - Incorrect (lipids can flip-flop, though rarely).
- **Option 3**: "Both lipids and proteins can flip-flop" - Incorrect (only lipids can flip-flop).
- **Option 4**: "Lipids can rarely flip-flop, and proteins cannot" - Correct.

6. **Conclusion**:
- The correct statement regarding the fluid mosaic model is that lipids can rarely flip-flop, while proteins cannot.

### Final Answer:
The correct option is: **Lipids can rarely flip-flop, and proteins cannot.**

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