Glycosylation is a post translational modification of lipids and proteins. Post translational modification of proteins and lipids is essential for their stability, proper folding, cell interactions and signaling. The transfer of initial sugar to glycoproteins or glycolipids occurs in the endoplasmic reticulum or on the membrane of endoplasmic reticulum. 

 

The subsequent addition of the many different sugars that make up a mature glycan is accomplished in the Golgi apparatus. Golgi membranes are embedded with glycosidases, glycosyltransferases, and nucleotide sugar transporters. The linkage of glycans to proteins and lipids is carried out by eleven biosynthetic pathways in eukaryotes.