Final answer:
Proteins exit the rough ER through vesicle transport to the Golgi for modification, followed by packaging into a vesicle for cell part delivery or plasma membrane integration, and finally may be secreted from the cell via secretory vesicles fusing with the plasma membrane.
Step-by-step explanation:
Proteins can exit the rough endoplasmic reticulum (RER) and participate in the secretion pathway in three primary ways. Once the proteins are synthesized on bound ribosomes on the RER’s surface, they are sequestered within membrane-bound compartments and follow specific pathways. These include:
- The vesicle which contains newly synthesized proteins travels from the rough ER and fuses with the cis face of the Golgi apparatus. In the Golgi, proteins are modified and sorted before proceeding.
- After the modifications in the Golgi, the protein is further packaged into a vesicle that can either place it into other cell parts where it will be used or transport it to the cell's plasma membrane.
- For exocytosis, the secretory vesicle merges with the plasma membrane, expelling its protein content outside the cell or embedding membrane proteins into the cell membrane.
A separate pathway involves polypeptide chains made on the rough ER getting inserted directly into the ER and are then transported to their various cellular destinations, particularly when they are proteins destined for the cell membrane.