Final answer:
The oligosaccharide is originally attached to a specialized lipid, called dolichol phosphate, in the ER membrane. It is then transferred to the amino (NH₂) group of a asparagine side chain on the protein, immediately after a target polypeptide emerges in the ER lumen during protein translocation.
Step-by-step explanation:
The oligosaccharide is attached to dolichol phosphate, transferred to an asparagine side chain of a polypeptide, and further modified in the Golgi apparatus to form glycoproteins. This process is an essential part of the synthesis and modification of glycoproteins, where proteins are tagged with carbohydrates in the rough endoplasmic reticulum (RER). This glycosylation process, which begins in the RER, continues as the proteins move through the Golgi apparatus, where additional sugar molecules are added, resulting in the formation of glycoproteins that are critical for various cellular functions.