Which of the following events does not occur in rough endoplasmic reticulum,

Options

A. Phospholipid synthesis
B. Cleavage of signal peptide
C. Protein glycosylation
D. Protein folding

Answer

To determine which event does not occur in the rough endoplasmic reticulum (RER), we need to analyze the functions of the RER and compare them with the options provided.

### Step-by-Step Solution:

1. **Understand the Structure of RER**: The rough endoplasmic reticulum is characterized by the presence of ribosomes on its surface. This structure is crucial for its function in protein processing.

2. **Identify Functions of RER**:
- **Protein Sorting**: The RER is involved in sorting proteins that are synthesized by the ribosomes. It helps direct these proteins to their appropriate destinations within the cell.
- **Protein Glycosylation**: The RER plays a role in glycosylation, which is the addition of carbohydrate groups to proteins, aiding in their stability and function.
- **Protein Folding**: The RER assists in the proper folding of proteins, ensuring they achieve their functional three-dimensional structures.
- **Cleavage of Signal Peptide**: The RER also participates in the cleavage of signal peptides, which are short sequences that direct the transport of proteins.

3. **Analyze the Options**:
- **Phospholipid Biosynthesis**: This process occurs primarily in the smooth endoplasmic reticulum (SER), not the RER.
- **Cleavage of Signal Peptide**: This occurs in the RER.
- **Protein Glycosylation**: This occurs in the RER.
- **Protein Folding**: This occurs in the RER.

4. **Conclusion**: Since phospholipid biosynthesis is a function of the smooth endoplasmic reticulum and not the rough endoplasmic reticulum, the correct answer is that phospholipid biosynthesis does not occur in the RER.

### Final Answer:
**Phospholipid biosynthesis does not occur in the rough endoplasmic reticulum.**

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