Final answer:
The SRP docks on the SRP receptor on the ER membrane. This interaction is crucial for directing the synthesis and proper insertion of secreted proteins into the rough endoplasmic reticulum, where they undergo folding and modifications, such as carbohydrate addition before being dispatched to their final destinations.
Step-by-step explanation:
In the synthesis and targeting of secreted proteins to the ER, SRP docks on the SRP receptor on the ER membrane. The SRP receptor is a protein complex located on the membrane of the rough endoplasmic reticulum (RER) that specifically recognizes the SRP-ribosome complex. Once the SRP has bound to the hydrophobic signal peptide of the nascent polypeptide, this halts elongation until the complex finds the RER membrane.
At this point, the SRP is detached from the growing polypeptide chain to allow translation elongation to resume through a translocation channel in the RER membrane. While in the RER lumen, the growing polypeptide begins to fold, and modifications such as carbohydrate addition may occur. This process ensures that proteins destined for secretion or for the cell membrane are accurately directed to the RER where protein synthesis can continue and post-translational modifications take place.