What role does the signal recognition particle (SRP) play?

The signal recognition particle (SRP) plays a crucial role in the translation and translocation process of proteins destined for the endoplasmic reticulum (ER). The primary function of SRP is to recognize and bind to specific peptide signals on nascent polypeptides that are being synthesized by ribosomes in the cytosol. Once the SRP binds to the signal sequence of the protein, it temporarily halts translation, which allows the ribosome-SRP complex to be directed to the ER membrane.

Once at the ER, the SRP interacts with the SRP receptor, facilitating the docking of the ribosome to the membrane of the ER. Subsequently, the ribosome resumes translation, and the growing polypeptide chain is translocated into the ER lumen, where it can undergo further modifications and folding necessary for proper function. This process ensures that proteins are accurately targeted to their correct cellular destinations, making the SRP integral to protein sorting and secretion pathways.

In contrast to the other options, the SRP does not directly synthesize proteins, transport them to the lysosome, or degrade misfolded proteins. Instead, its specific role in directing ribosomes to the ER highlights its importance in the pathway of protein synthesis and sorting.