You are studying the processes of glycoprotein synthesis using a cell culture system. Your experiments are focused on the attachment of oligosaccharides to asparagine residues in proteins as they transit the ER. Your experiments detect that the cells you are using are incapable of the initial transfer of nucleotide-activated sugars. Given these results, which of the following is most likely deficient in these cells?
A) arachidonic acid
B) asparagine
C) dolichol pyrophosphate
D) glucose 6-phosphate
E) serine

Question

Quizplus · Accepted Answer

Dolichol pyrophosphate is a lipid carrier molecule that is essential for the initial transfer of oligosaccharides to asparagine residues in the process of N-linked glycosylation in the endoplasmic reticulum. A deficiency in dolichol pyrophosphate would impair this process.  The formation of N-linked glycoproteins occurs in the endoplasmic reticulum (ER) through cotranslational addition of a preassembled carbohydrate core structure that is delivered via the carbohydrate-dolichol lipid intermediate. The preassembled carbohydrate core structure comprises 3 terminal residues of glucose attached to a branched cluster of 9 mannose residues that are in turn attached to 2 GlcNAc residues attached to dolichol pyrophosphate. Lack of dolichol pyrophosphate would prevent the ability to incorporate oligosaccharides onto appropriate asparagine residues in normally N-linked glycoproteins.

You Are Studying the Processes of Glycoprotein Synthesis Using a Cell