Q.13 In N-linked glycosylation, the oligosaccharide chain is attached to protein by
- (A) asparagine
- (B) arginine
- (C) serine
- (D) threonine
In N-linked glycosylation, the oligosaccharide chain attaches to the asparagine residue of proteins via an N-glycosidic bond in the ER. This SEO-optimized article answers the MCQ: In N-linked glycosylation, the oligosaccharide chain is attached to protein by (A) asparagine, (B) arginine, (C) serine, (D) threonine—essential for biochemistry, biotechnology, and mammalian cell culture students.
Correct Answer: Option (A) Asparagine
N-linked glycosylation links pre-assembled Glc3Man9GlcNAc2 oligosaccharides from dolichol pyrophosphate to asparagine in the consensus sequence Asn-X-Ser/Thr (X ≠ Pro), catalyzed by oligosaccharyltransferase (OST) co-translationally.
This modification drives protein folding (calnexin cycle), quality control, and trafficking in your mammalian cell culture research, with ~1-25% of eukaryotic proteins glycosylated.
Explanation of All Options
N- vs O-glycosylation targets different amino acid side chains:
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(A) Asparagine: Correct. N-glycosylation forms amide bond with Asn’s side-chain nitrogen in ER lumen.
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(B) Arginine: Incorrect. No glycosylation occurs; arginine’s guanidinium supports protein-protein interactions.
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(C) Serine: Incorrect. O-GalNAc glycosylation target (mucin-type) in Golgi, not N-linked.
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(D) Threonine: Incorrect. Also O-linked target with Ser, forming O-glycosidic bonds post-translationally.
Option Amino Acid Glycosylation Type Bond Formed Correct/Incorrect (A) Asparagine Asn N-linked N-glycosidic (amide) Correct (B) Arginine Arg None N/A Incorrect (C) Serine Ser O-linked (Golgi) O-glycosidic Incorrect (D) Threonine Thr O-linked (Golgi) O-glycosidic Incorrect Biotechnology Relevance
Proper N-glycosylation in CHO cells ensures therapeutic efficacy (e.g., tPA folding/stability from Q.5), directly impacting your animal cell culture and enzyme kinetics work. Defects cause congenital disorders of glycosylation (CDG).
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