Final answer:
Glycosylation within the Golgi stacks adds a specific sequence of sugars to proteins, resulting in functional glycoproteins that are essential for their correct cellular localization and function.
Step-by-step explanation:
The specific sequence of sugars is added to a protein as it goes through Golgi stacks during the process known as glycosylation. Proteins initially synthesized in the rough endoplasmic reticulum (RER) receive a core glycoside. As they pass through the Golgi apparatus, undergoing glycosylation, more sugars are enzymatically added, further modifying the proteins to become functional glycoproteins. This modification is essential for determining the protein's final destination, such as membranes, extracellular fluids, lysosomes, or peroxisomes. The fully modified glycoproteins then travel via vesicles to their destinations; those targeting the plasma membrane have their sugar chains positioned on the exterior surface of the cell, playing a vital role in cell-to-cell communication and other cellular functions.