rough endoplasmic reticulum

What is the Rough Endoplasmic Reticulum (RER)?

A network of interconnected membranes found in eukaryotic cells, characterized by the presence of ribosomes on its cytoplasmic surface.

What gives the RER its "rough" appearance?

The numerous ribosomes attached to its outer surface.

Where is the RER typically located within a cell?

It is continuous with the outer membrane of the nuclear envelope and extends throughout the cytoplasm.

What is the primary function of the RER in protein synthesis?

It synthesizes proteins that are destined for secretion, insertion into cellular membranes, or delivery to other organelles such as the Golgi apparatus, lysosomes, and endosomes.

What types of proteins are synthesized by ribosomes on the RER?

Transmembrane proteins, soluble proteins for secretion, and proteins destined for the lumen of the ER itself, Golgi, lysosomes, and endosomes.

Besides synthesis, what other critical processes occur in the RER lumen?

Protein folding, assembly of multi-subunit proteins, initial glycosylation (addition of carbohydrate chains), and the formation of disulfide bonds.

What happens to misfolded or improperly assembled proteins in the RER?

They are usually retained by chaperone proteins and eventually targeted for degradation via the proteasome through a process called ER-associated degradation (ERAD).

How do polypeptide chains enter the RER lumen or membrane during translation?

As the polypeptide chain emerges from the ribosome, it is cotranslationally translocated into the RER lumen or embedded into its membrane through a protein translocator channel.

What is the relationship between the RER and the Golgi apparatus?

The RER synthesizes and initially processes proteins that are then transported (typically in vesicles) to the Golgi apparatus for further modification, sorting, and packaging.

What is the significance of the RER in the overall secretory pathway?

It serves as the cellular entry point for proteins entering the secretory pathway, acting as a crucial site for quality control before proteins are dispatched to their final destinations