Final answer:
SRP plays a pivotal role in transmembrane protein synthesis by pausing elongation to bind to the signal peptide, then guiding the ribosome to the RER where translation resumes and the protein is integrated into the membrane. Following synthesis, the protein is sorted and directed to its final destination.
Step-by-step explanation:
The Signal Recognition Particle (SRP) is crucial in the synthesis and insertion of transmembrane proteins into the membrane of the Rough Endoplasmic Reticulum (RER). Firstly, an SRP binds to the hydrophobic signal peptide that emerges from a ribosome. This binding halts the elongation process of the protein until the SRP-ribosome complex locates the RER membrane. Upon reaching the RER, the complex interacts with an SRP receptor which facilitates attachment to the membrane.
After successful attachment, the SRP detaches, allowing translation to resume. The protein elongates through a channel in the RER membrane where a signal peptidase catalyses the hydrolysis of the signal peptide, embedding it in the RER membrane. The polypeptide continues to elongate and begins folding within the RER, often involving additional sequences like stop-transfer sequences that determine the protein's position in the membrane.
Once the protein synthesis is complete, it is packaged into transport vesicles, which move from the ER to the Golgi apparatus, and further sorting occurs to direct the protein to its functional destination. Not only is the SRP vital in guiding proteins to the RER, but it also maintains the nascent polypeptide in an unfolded state to prevent premature folding.