The biosynthesis of N-linked glycans occurs via 3 major steps:
#Synthesis of dolichol-linked precursor oligosaccharide
#En bloc transfer of precursor oligosaccharide to protein
#Processing of the oligosaccharide
Synthesis, en bloc transfer and initial trimming of precursor oligosaccharide occurs in the endoplasmic reticulum (ER). Subsequent processing and modification of the oligosaccharide chain are carried out in the Golgi apparatus.
The synthesis of glycoproteins is thus spatially separated in different cellular compartments. Therefore, the type of N-glycan synthesized, depends on its accessibility to the different enzymes present within these cellular compartments.
However, in spite of the diversity, all N-glycans are synthesized through a common pathway with a common core glycan structure.
The core glycan structure is essentially made up of two N-acetyl glucosamine and three mannose residues. This core glycan is then elaborated and modified further, resulting in a diverse range of N-glycan structures.