Golgi complex oligosaccharide biosynthesis

Many secretory and membrane proteins are modified in the lumen of the ER. Protein glycosylation, the addition of covalently bound oligosaccharide chains, is a common reaction in the ER lumen and the Golgi complex. Most proteins in the ER lumen destined for secretion from the cell or for transport to other intracellular sites are glycoproteins. The carbohydrate content of glycoproteins can vary from 0.5 to 80% or more of the glycoprotein mass. Glycoprotein structures were described in Chapter 9, and their biosynthesis are covered in Chapter 20. 

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