Question

The signal-recognition particle (SRP) ...

A. is a heterodimeric protein.
B. transiently inhibits translation and polypeptide elongation by binding to and inhibiting the elongation factors.
C. accompanies the nascent polypeptide all the way into the ER lumen.
D. binds GTP.
E. is permanently attached to the cytosolic face of the ER membrane, thus bringing the ribosomes into close proximity of the translocon.

Answer 1

The signal-recognition particle (SRP) accompanies the nascent polypeptide all the way into the ER lumen.

Step-by-step explanation:

The signal-recognition particle (SRP) is a ribonucleoprotein complex composed of both RNA and protein components. Its main role is to recognize and target newly synthesized proteins that have a signal peptide to the endoplasmic reticulum (ER) membrane for proper localization and insertion.

Option C is correct. The SRP accompanies the nascent polypeptide all the way into the ER lumen. It binds to the signal peptide of the growing polypeptide chain and guides it to the SRP receptor on the ER membrane.

Option E is incorrect. The SRP is not permanently attached to the cytosolic face of the ER membrane. It transiently interacts with the ER membrane through the SRP receptor.