Question

I-Cell paticnts lack the enzyme that transfers N-acetylglucosamine phosphate to high mannose type oligosaccharides on the protein. This \(N\) -linked glycosylation A. occurs only after the protein has been completely translated and folded. B. does not require any specific amino acid sequence. C. occurs by transfer of an oligosaccharide chain from a dolichol phosphate carrier to the protcin. D. has the oligosaccharide chain attached to serine or threonine. E. contains only mannoses in the chain.

Short answer

Answer: N-linked glycosylation in I-Cell patients occurs by transfer of an oligosaccharide chain from a dolichol phosphate carrier to the protein.

Step-by-step solution

Analyzing each answer choice

Let's analyze each statement one by one and check if it is correct or incorrect related to N-linked glycosylation: A. N-linked glycosylation occurs during the translation and folding of the protein, not after the protein has been completely translated and folded. So, this statement is incorrect. B. N-linked glycosylation does require a specific amino acid sequence. The consensus sequence is Asn-X-Ser/Thr, where X can be any amino acid except proline. So, this statement is incorrect. C. N-linked glycosylation occurs by transfer of an oligosaccharide chain from a dolichol phosphate carrier to the protein. This statement is correct. D. In N-linked glycosylation, the oligosaccharide chain is attached to the nitrogen atom of an asparagine (Asn) residue, not serine or threonine. So, this statement is incorrect. E. The oligosaccharide chain in N-linked glycosylation contains not only mannoses but also other sugars like N-acetylglucosamine and sometimes fucose and galactose. So, this statement is incorrect.

Choose the correct statement

Based on our analysis in Step 1, we can conclude that the correct statement about N-linked glycosylation in I-Cell patients is: C. occurs by transfer of an oligosaccharide chain from a dolichol phosphate carrier to the protein.