Final answer:
The transfer of polypeptides into the ER during synthesis is called cotranslational import. This process involves the N-terminal signal sequence of the polypeptide guiding it to the RER where it may become an integral membrane protein or be modified and sorted for transport.
Step-by-step explanation:
The transfer of polypeptides into the endoplasmic reticulum (ER) during their synthesis is known as cotranslational import. While a polypeptide chain is being synthesized by a ribosome, its N-terminal signal sequence guides it to the rough ER (RER), where cotranslational import occurs.
In the case of integral membrane proteins, the presence of stop-transfer sequences within their structure will cause them to be embedded within the membrane of the RER instead of being transported completely through it. Packaging of these proteins within the RER involves their modification and sorting for subsequent transport to other cellular destinations.