Ribosomes, when associated with ER. attach with their

Options

A. Smaller subunit
B. Larger subunit (60S)
C. 80S subunit
D. Either by smaller or by larger subunits

Answer

**Step-by-Step Solution:**

1. **Understanding Ribosomes**: Ribosomes are small cellular structures responsible for protein synthesis. They consist of two subunits: a smaller subunit and a larger subunit.

2. **Subunits of Ribosomes**: The smaller subunit is typically referred to as the 30S subunit, while the larger subunit is referred to as the 50S or 60S subunit, depending on the organism. These subunits contain ribosomal RNA (rRNA) and proteins.

3. **Function of Ribosomal Subunits**:
- The smaller subunit (30S) is primarily responsible for decoding the genetic message by binding to messenger RNA (mRNA).
- The larger subunit (50S or 60S) has a catalytic function, which means it helps in forming peptide bonds between amino acids during protein synthesis. It binds to transfer RNA (tRNA).

4. **Association with Endoplasmic Reticulum (ER)**: Ribosomes can associate with the endoplasmic reticulum (ER), specifically the rough endoplasmic reticulum (RER). This association is not permanent; ribosomes can attach and detach from the ER.

5. **Mechanism of Attachment**: The attachment of ribosomes to the ER occurs through a glycoprotein known as ribophorin. This protein acts as a receptor that helps bind the ribosome to the outer surface of the rough ER.

6. **Conclusion**: In summary, ribosomes attach to the endoplasmic reticulum via their larger subunit, which binds to the ribophorin on the rough ER, facilitating protein synthesis.

**Final Answer**: Ribosomes, when associated with the endoplasmic reticulum, attach with their larger subunit.

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