Final answer:
Core oligosaccharides are initially added to the nascent polypeptide in the RER and undergo further glycosylation in the Golgi apparatus before being packaged and transported to the plasma membrane, where they serve functional roles on the cell surface.
Step-by-step explanation:
The process of glycoprotein synthesis involves multiple steps occurring within different compartments of the cell. Initially, oligosaccharides begin their synthesis in the rough endoplasmic reticulum (RER), where a core glycoside is created and partial glycans are enzymatically linked to the amino acids of a membrane protein. This nascent polypeptide then receives further modifications involving the addition of sugars as it moves through the Golgi apparatus (GA).
Upon departing the ER, transport vesicles containing the protein cargo fuse with the Golgi apparatus on its cis face, where they begin their journey through this organelle. As the proteins progress from the cis face to the trans face of the Golgi, they are subjected to additional modifications, which often include the attachment of short chains of sugar molecules, to finally complete the glycoprotein synthesis.
These fully synthesized glycoproteins are then packaged in transport vesicles that bud from the trans Golgi vesicles. When these vesicles fuse with the plasma membrane, the glycoproteins, now bearing their sugar modifications, are positioned on the external cell surface, where they play critical roles in cell signaling and recognition.