Question

During synthesis of N-linked glycosylated proteins in mammalian cells, which one of the following compositions of sugars is originally added as a core through dolichol-phosphate precursor?

• A. 2 moieties of N-acetylglucosamine, 9 moieties of mannose and 3 moieties of glucose
• B. 2 moieties of N-acetylglucosamine, 5 moieties of mannose and 3 moieties of glucose
• C. 1 moiety of N-acetylglucosamine, 5 moieties of mannose and 3 moieties of glucose
• D. 2 moieties of N-acetylglucosamine, 9 moieties of mannose and 1 moiety of glucose

Hint:

The core oligosaccharide in N-linked glycosylation typically consists of 2 GlcNAc, 9 mannose, and 3 glucose moieties, which are added to proteins during their synthesis.

Answer 1

The Correct Option is A

Step 1: Understanding the N-linked glycosylation process.
In N-linked glycosylation, the core oligosaccharide is added to a protein during its synthesis. This core oligosaccharide consists of 2 N-acetylglucosamine (GlcNAc) residues, followed by 9 mannose and 3 glucose residues, which are then attached to the dolichol-phosphate precursor.

Step 2: Analyzing the options.
- (A) 2 moieties of N-acetylglucosamine, 9 moieties of mannose and 3 moieties of glucose: This is the correct composition of the core oligosaccharide used in N-linked glycosylation.
- (B) 2 moieties of N-acetylglucosamine, 5 moieties of mannose and 3 moieties of glucose: Incorrect, as it has fewer mannose residues than the core structure.
- (C) 1 moiety of N-acetylglucosamine, 5 moieties of mannose and 3 moieties of glucose: Incorrect, as it lacks the required number of N-acetylglucosamine moieties.
- (D) 2 moieties of N-acetylglucosamine, 9 moieties of mannose and 1 moiety of glucose: Incorrect, as the correct structure contains 3 glucose moieties.

Final Answer: \[ \boxed{\text{(A) 2 moieties of N-acetylglucosamine, 9 moieties of mannose and 3 moieties of glucose.}} \]