The term "endo" refers to within the cytoplasm and a reticulum is a network. Thus the endoplasmic reticulum is a series of interconnected, intracytoplasmic, membrane bounded sacs.
The "rough" appearance of the rough endoplasmic reticulum (RER) results from the presence of ribosomes that are bound to the cytosolic side of the endoplasmic reticulum membrane. The presence of ribosomes on the RER indicates that it is involved in
The smooth endoplasmic reticulum (SER) has no such bound ribosomes and is not involved in protein synthesis. However, the SER is involved in
cholesterol metabolism,
membrane synthesis,
detoxification,
Ca++ storage along with other cellular processes.
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