Assembly of the dolichol-linked precursor in N-glycosylation and steps affected in type I CDG. The Man5GlcNAc2-PP-Dol intermediate is synthesized on the cytoplasmic side of the ER membrane by the successive transfer of GlcNAc and mannose from UDP-GlcNAc and GDP-Man. The Dol-PP-heptasaccharide is then translocated across the ER membrane. Four more mannoses and then 3 glucoses are added from Dol-P-Man and Dol-P-glucose, after which the oligosaccharide is transferred to certain asparagines in protein by oligosaccharyltransferase (OT-ase). Shown are the steps in the formation of GDP-Man and Dol-P-Man and the other glycosylation pathways in which Dol-P-Man can serve as donor. The steps blocked by the known type I CDGs and the genes affected are indicated. F-6-P, fructose-6-P; M, mannose; G, glucose; GN, glucosamine; PI, phosphatidylinositol.