Rough endoplasmic reticulum glycosylation

The core protein is synthesized on and enters the rough endoplasmic reticulum (RER). The protein is then glycosylated by membrane-bound transferases as it moves through the ER. 

Hirschberg, C. B., and M. D. Snider, Topography of glycosyl-ation in the rough endoplasmic reticulum and the Golgi apparatus. Ann. Rev. Biochem. 56 63-87, 1987. 

Secretory proteins have an N-terminal signal peptide which targets the protein to be synthesized on the rough endoplasmic reticulum (RER). During synthesis it is translocated through the RER membrane into the lumen. Vesicles then bud off from the RER and carry the protein to the Golgi complex, where it becomes glycosylated. Other vesicles then carry it to the plasma membrane. Fusion of these transport vesicles with the plasma membrane then releases the protein to the cell exterior. 

The answer is e. (Murray, pp 452-467. Scriver, pp 3-45. Sack, pp 1—40. Wilson, pp 101-120.) Protein synthesis occurs in the cytoplasm, on groups of free ribosomes called polysomes, and on ribosomes associated with membranes, termed the rough endoplasmic reticulum. However, proteins destined for secretion are only synthesized on ribosomes of the endoplasmic reticulum and are synthesized in such a manner that they end up inside the lumen of the endoplasmic reticulum. From there the secretory proteins are packaged in vesicles. The Golgi apparatus is involved in the glycosylation and packaging of macromolecules into membranes for secretion. 

Perez, M., and Hirschberg, C. (1986). Topography of glycosylation reactions in the rough endoplasmic reticulum membrane. J. Biol. Chem. 261, 6822-6830. 

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