Carbohydrate linkage to Noncarbohydrates

Carbohydrates can be attached by glycosidic bonds to noncarbohydrate structures, including purine and pyrimidine bases (found in nucleic acids), aromatic rings (such as those found in steroids and bilirubin), proteins (found in glycoproteins and proteoglycans), and lipids (found in glycolipids). If the group on the noncarbohydrate molecule to which the sugar is attached is an –NH2 group, then the bond is called an N-glycosidic link. If the group is an –OH, then the bond is an O-glycosidic link (Fig.1). [Note: All sugar-sugar glycosidic bonds are O-type linkages.]

Figure 1: Examples of N- and O-glycosidic bonds in glycoproteins.