A mature antibody carries branched carbohydrate chains linked to particular asparagine side chains. In which cellular compartment were those sugar chains first attached to the protein?

Core Concept

N-linked glycosylation begins in the rough ER, where a preassembled oligosaccharide carried on dolichol transfers onto asparagine residues as the growing chain enters the lumen. Later stations in the Golgi trim mannose residues and add other sugars, remodeling the chains. The initial attachment event, however, happens only in the ER.