Final answer:
The rough endoplasmic reticulum (RER) is responsible for the synthesis and packaging of proteins. Ribosomes are attached to the membrane of the RER, and as they build amino acid chains, the chains are pushed into the ER. When a protein is complete, the RER pinches off a vesicle containing the protein. The vesicle can then move to the cell membrane or the Golgi apparatus.
Step-by-step explanation:
Rough endoplasmic reticulum (RER) is studded with ribosomes, which gives it a "rough" appearance. These ribosomes make proteins that are then transported from the ER in small sacs called transport vesicles. The transport vesicles pinch off the ends of the ER. The RER works with the Golgi apparatus to move new proteins to their proper destinations in the cell. The membrane of the RER is continuous with the outer layer of the nuclear envelope.