Final answer:
The rough ER is characterized by ribosomes on its surface, which gives it a rough texture, distinguishing it from the smooth ER that lacks ribosomes. These ribosomes are essential for the synthesis of proteins destined for export or use within the cell.
Step-by-step explanation:
The rough endoplasmic reticulum (RER) is named for its rough appearance which is due to the presence of ribosomes attached to its cytoplasmic surface. Unlike the smooth endoplasmic reticulum (SER), which lacks these ribosomes, the RER appears studded when viewed through an electron microscope. These ribosomes are the site of protein synthesis, where they translate mRNA into proteins that are either secreted from the cell, incorporated into the cell's plasma membrane, or shipped to an organelle.
Furthermore, the rough ER is involved in the production of proteins that are transported out of the cell, which are then carried in small sacs called transport vesicles that pinch off the ends of the RER. The RER is continuous with the nuclear envelope, emphasizing its important role in protein synthesis and transport within the cell.