Rough endoplasmic reticulum

Rough endoplasmic reticulum is a type of endoplasmic reticulum in which the cytoplasmic, membrane-lined cavities are covered with ribosomes.

The ribosomes are attached to the outer, cytoplasmic surface of the rER by specialized protein receptors. The ribosomes may be linked along the membrane surface by a strand of messenger RNA to create a polyribosome. The ribosomes are the main reason rER takes up basophilic stains for light microscopy.

The rER functions to produce and compartmentalise proteins, lipids and other cellular constituents. Polypeptide chains are manufactured at the ribosome and then are either:

• set free for passage into the cytoplasm
• incorporated into the membrane of the rER for further packaging into plasma membrane or membrane or organelles throughout the body
• extruded into the cisternal space of the rER for later packaging into organelles e.g. lysosome, or extracellular secretion

There are a number of non-ribosomal proteins in the membrane of the rER which are involved in further processing molecules e.g. post-translational glycosylation, active transport of lipid molecules across the rER membrane.