The endoplasmic reticulum is a continuous membrane system that forms a series of flattened sacs within the cytoplasm of the eukaryotic cells. It serves multiple functions like the synthesis, folding, modification, and transport of proteins. All eukaryotic cells contain an endoplasmic reticulum. There are differences in certain physical and functional characteristics distinguish the two types of ER which are known as rough ER and smooth ER. Glycosylation is an enzyme directed site-specific process. The ribosomes attached to the surface of endoplasmic reticulum are involved in protein synthesis. The synthesised proteins are passed into the lumen of the endoplasmic reticulum or golgi complex and the glycosylation of proteins takes place, i.e., an oligosaccharide is added to them.