Ribophorins/SRP receptors are required for

Options

A. Synthesis of ribosomes in nucleolus
B. Attachment of ribosomes over R.E.R
C. Attachment of ribosome subunits
D. Attachment of mRNA to ribosomes for protein synthesis.

Answer

**Step-by-Step Solution:**

1. **Understanding SRP Receptors**:
- SRP stands for Signal Recognition Particle. These are essential components in the process of protein synthesis and targeting within the cell.
- SRP receptors are proteins located on the rough endoplasmic reticulum (RER) that facilitate the docking of ribosomes to the RER.

2. **Role of Rough Endoplasmic Reticulum (RER)**:
- The rough endoplasmic reticulum is studded with ribosomes, which gives it a "rough" appearance. It plays a critical role in the synthesis of proteins that are either secreted from the cell or incorporated into cellular membranes.

3. **Function of Ribophorins**:
- Ribophorins are glycoproteins found on the rough endoplasmic reticulum. They are part of the SRP receptor complex and are crucial for the attachment of ribosomes to the RER.

4. **Mechanism of Ribosome Attachment**:
- When a nascent protein is synthesized, the SRP binds to the signal sequence of the protein. This complex then interacts with the SRP receptor on the RER, allowing the ribosome to attach to the RER and continue protein synthesis directly into the lumen of the RER.

5. **Conclusion**:
- Therefore, the primary requirement of ribophorins/SRP receptors is to facilitate the attachment of ribosomes to the rough endoplasmic reticulum, enabling the synthesis of proteins that are destined for secretion or for use in the cell membrane.

**Final Answer**: Ribophorins/SRP receptors are required for the attachment of ribosomes to the rough endoplasmic reticulum.

---