Rough endoplasmic reticulum is associated with

Options

A. fat synthesis
B. lipid synthesis
C. protein synthesis
D. steroid synthesis

Explanation

### Step-by-Step Solution:

1. **Identify the Structure**: The rough endoplasmic reticulum (RER) is a type of endoplasmic reticulum that is characterized by the presence of ribosomes on its cytoplasmic surface.

2. **Understand the Function**: The presence of ribosomes gives the RER its "rough" appearance and is crucial for its primary function, which is the synthesis of proteins.

3. **Location in the Cell**: The RER is typically located near the nucleus of the cell, which is important for the synthesis and processing of proteins that are either secreted from the cell or incorporated into cellular membranes.

4. **Types of Proteins Synthesized**: The RER is responsible for synthesizing various types of proteins, including membrane proteins, cytosolic proteins, and lysosomal proteins.

5. **Distinguish from Smooth ER**: It is important to note that the smooth endoplasmic reticulum (SER) is involved in lipid and steroid synthesis, while the RER is specifically associated with protein synthesis.

6. **Conclusion**: Therefore, the rough endoplasmic reticulum is primarily associated with protein synthesis due to the presence of ribosomes.

### Final Answer:
Rough endoplasmic reticulum is associated with **protein synthesis**.

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