ABSTRACT
The synthesis of O-linked oligosaccharides occurs by the sequential addition of monosaccharide units to the newly synthesized protein as it passes through the Golgi complex. In addition, several proteins are known to be attached to the plasma membrane via a specific structure that involves carbohydrate, namely a glycosyl phosphatidylinositol anchor. Most proteins made by ribosomes on the rough endoplasmic reticulum (RER) are glycoproteins, that is they contain short chains of carbohydrates covalently linked to them during passage through the RER and Golgi complex. The oligosaccharide is initially synthesized on a dolichol phosphate carrier that is anchored to the RER membrane. N-linked oligosaccharides are not synthesized by adding monosaccharides directly to the protein but instead the oligosaccharide is made on a lipid carrier called dolichol phosphate. Mannose residues and other monosaccharides are also added to the oligosaccharide in the Golgi to generate either the high mannose or complex type of oligosaccharide.
