Where does glycosylation of protein occur?

Options

A. Endoplasmic reticulum
B. Lysosomes
C. Mitochondria
D. Chloroplast

Answer

**Step-by-Step Solution:**

1. **Understanding Glycosylation**: Glycosylation is the process where sugar molecules (glycans) are added to proteins. This modification is crucial for protein folding, stability, and function.

2. **Identifying the Sites of Glycosylation**: Glycosylation primarily occurs in two cellular locations:
- **Endoplasmic Reticulum (ER)**: This is where N-linked glycosylation occurs. In this process, sugar moieties are attached to the nitrogen atom of asparagine residues in the protein.
- **Golgi Complex**: This is where O-linked glycosylation occurs, involving the addition of sugars to the oxygen atom of serine or threonine residues.

3. **Evaluating the Options**:
- **Endoplasmic Reticulum**: Correct, as it is one of the primary sites for glycosylation (N-linked).
- **Lysosomes**: Incorrect, as they are involved in degradation and recycling of cellular components, not glycosylation.
- **Mitochondria**: Incorrect, as they are primarily involved in energy production (ATP generation).
- **Chloroplasts**: Incorrect, as they are involved in photosynthesis, not glycosylation.

4. **Conclusion**: The correct answer is the **Endoplasmic Reticulum**, as it is one of the main sites where glycosylation occurs.

**Final Answer**: Endoplasmic Reticulum

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