Answer:
The correct answer is: in the rough endoplasmic reticulum.
A protein that ultimately functions in the plasma membrane of a cell is most likely to have been synthesized in the rough endoplasmic reticulum.
Explanation:
The endoplasmic reticulum constitutes a system of membrane-limited cavities (cisterns). There are two different forms of endoplasmic reticulum: rough and smooth, which have a different appearance and structure. The rough endoplasmic reticulum appears in many cells as a set of cisternae stacked in parallel. Its membranes are associated with ribosomes, its main function is to synthesize proteins with ribosomes attached to its membrane. The synthesized proteins pass from the rough endoplasmic reticulum to the smooth endoplasmic reticulum, then to the Golgi apparatus and from there, to the lysosomes, to the plasma membrane or to the exterior. Before being transported to other cytoplasmic organelles (Golgi apparatus, lysosomes), to the plasma membrane or to the exterior of the cell, they must be glycosylated to become glycoproteins.
