Exploring the Rough ER:
The rough ER is named “rough” because it has bounded ribosomes attached to it. These ribosomes secrete proteins, and these proteins are further developed inside the rough ER. First, the ribosome produces a polypeptide chain that is soon threaded into the rough ER through a protein complex pore. The rough ER is directly continuous with the nuclear membrane, which explains why it has such similar pore systems. After the chain enters the ER lumen (aka cisternal space), it folds into the structure of the desired protein. Such secretary proteins are mostly glycoproteins, which are basically proteins with covalently bonded carbohydrates (remember, this started out as a long polypeptide chain!). Once the proteins are completed, the rough ER sends the secretary proteins in transport vesicles to keep them from mixing with the free ribosome proteins in the cytoplasm. These vescicles are formed in a part of the rough ER called the transitional ER, which is on the opposite side of the ER that is connected to the nucleus.
Rough ER is also important in that it creates much of the membranes for the cell by just adding more proteins and phospholipids to the original ER membrane. While the rough ER makes some of its own phospholipids using enzymes in the ER membrane, other proteins destined to be membrane proteins are lodged into the ER membrane so that when the new membrane is made, the proteins would be there ready to go.