Final answer:
The movement of a polypeptide through the translocon in the ER is driven by the GTP hydrolysis catalyzed by the translocase, also known as elongation factor-G (EF-G).
Step-by-step explanation:
The process that drives a polypeptide through the translocon in the endoplasmic reticulum (ER) is powered by GTP hydrolysis. During the elongation stage of protein synthesis, translocase, also known as elongation factor-G (EF-G), catalyzes the hydrolysis of GTP. This activity moves the ribosome along the mRNA, allowing the polypeptide to pass through the translocon into the lumen of the ER, where it begins to fold into its functional three-dimensional structure. The energy for this translocation event comes specifically from the GTP hydrolyzed by the G protein elongation factor involved in the elongation cycle of protein synthesis.