Structure of Dolichol and their function during protein N-glycosylation. (A) Structure of Dolichol, where n is dependent on particular cis-prenyltransferase. Dolichol phosphate is an isoprenoid compound (90-100 carbons total) made from dolichol by phosphorylation. Dolichol phosphate performs important functions in synthesis of N-linked glycoproteins, as illustrated in (B). Dolichol phosphate is the structure upon which the complex oligosaccharide is made before transfer to the target protein. The addition of the first moiety, N-acetylglucosamine from UDP-N-acetylglucosamine, can be blocked by the antibiotic, tunicamycin. After assembly of the oligosaccharide is complete, the carbohydrate structure is transferred from dolichol phosphate to an asparagine residue of a target protein having the sequence Asn-x-Ser/Thr, where × is any amino acid. As also shown in (B), Dolichol phosphate can also act as a carrier of sugars to oligosaccharide chain synthesis assembly; such activated sugars include dolichol-P-mannose and dolichol-P-glucose.