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The smooth endoplasmic reticulum is a membrane system within the cytoplasm of eukaryotic cells and it is involved in synthesis, modification and transport of proteins. It is called smooth because there are no ribosomes attached to the surface.

 

The smooth ER in particular synthesize lipids, including cholesterol and phospholipids, for the cell membrane. Smooth ER also synthesize of steroid hormones from cholesterol and it also detoxify drugs and chemicals.