Final Answer:
The ER signal sequence on a growing polypeptide chain is recognized by a signal recognition particle (SRP) in the cytosol. This interaction guides the ribosome and its polypeptide to the ER membrane. Therefore, the correct answer is C. guides the ribosome and its polypeptide to the ER membrane.
Step-by-step explanation:
The signal recognition particle (SRP) plays a crucial role in directing the ribosome and the attached polypeptide chain to the endoplasmic reticulum (ER) membrane. This process involves a recognition event where the SRP recognizes the ER signal sequence on the growing polypeptide chain. This recognition event initiates the binding of the SRP to the ribosome, forming a complex.
Once the SRP-ribosome-polypeptide complex is formed, it targets the complex to the ER membrane. This targeting is essential for the correct localization of the polypeptide chain. The SRP interacts with the SRP receptor on the ER membrane, facilitating the transfer of the ribosome and the polypeptide chain to the translocation channel in the ER membrane. Subsequently, the synthesis of the polypeptide chain continues through the translocation channel into the ER lumen.
In summary, the correct answer, option C, reflects the accurate sequence of events during the recognition of the ER signal sequence by the SRP. This interaction guides the ribosome and its attached polypeptide chain to the ER membrane, ensuring proper localization and further synthesis within the endoplasmic reticulum.
Therefore, the correct answer is C. guides the ribosome and its polypeptide to the ER membrane.