Final answer:
Oligosaccharides are attached to the amino acid asparagine (Asn) through N-glycosidic linkages during glycoprotein synthesis. This occurs in the rough endoplasmic reticulum and is part of the glycoprotein's journey to the cell surface where it becomes part of the cell's glycocalyx.
Step-by-step explanation:
For N-glycosidic linkages, oligosaccharides are attached to the amino acid asparagine (Asn).
The process of attaching oligosaccharides to asparagine residues occurs in the rough endoplasmic reticulum (RER) where partial glycans are linked enzymatically to the asparagine residue within the consensus sequence Asn-x-Ser/Thr (x can be any amino acid except proline).
This event is part of the glycoprotein synthesis pathway. As proteins travel through the Golgi apparatus and onward to the cell surface, they undergo further glycosylation which results in the formation of a complete glycoprotein structure that is present on the cell surface as a component of the glycocalyx.
The attachment site on asparagine is through the amide nitrogen in the side chain, which forms a bond with the monosaccharide.
In contrast, O-glycosidic linkages occur on the hydroxyl group of serine or threonine residues. It is important to understand the distinction between N- and O-glycosylation as they have different amino acid requirements and implications in protein function and cell signaling.