Which of the following events does not occur in rough endoplasmic reticulumn?

Options

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

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. **Understanding the Rough Endoplasmic Reticulum (RER)**:
- The RER is characterized by the presence of ribosomes on its surface, which gives it a "rough" appearance. These ribosomes are crucial for protein synthesis.

2. **Functions of the RER**:
- **Protein Folding**: The RER is involved in the folding of proteins. After proteins are synthesized, they need to fold into their functional forms. This is a key function of the RER.
- **Glycosylation**: The RER also plays a role in glycosylation, which is the addition of carbohydrate groups to proteins. This modification is essential for proper protein function and stability.
- **Cleavage of Signal Proteins**: The RER is involved in the cleavage of signal peptides, which are short sequences that direct the transport of proteins.

3. **Identifying the Event that Does Not Occur in RER**:
- The question asks for an event that does not occur in the RER. The functions listed (protein folding, glycosylation, and cleavage of signal proteins) are all performed by the RER.
- However, **phospholipid synthesis** is not a function of the RER; it occurs in the smooth endoplasmic reticulum (SER). The SER is responsible for lipid synthesis, including phospholipids.

4. **Conclusion**:
- Therefore, the event that does not occur in the rough endoplasmic reticulum is **phospholipid synthesis**.

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

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