Glycogenin is a key protein in glycogen metabolism. Which statement accurately describes its function?
- A It adds glucose residues from UDP-glucose to the non-reducing ends of glycogen, extending the chain
- B It self-glucosylates to form a short glucose primer covalently attached to its tyrosine residue, which glycogen synthase then extends ✓
- C It catalyzes the formation of alpha-1,6 branch points in glycogen
- D It phosphorylates glycogen phosphorylase to initiate glycogenolysis
Correct answer: B. It self-glucosylates to form a short glucose primer covalently attached to its tyrosine residue, which glycogen synthase then extends
Explanation
Glycogenin acts as both enzyme and substrate: it uses UDP-glucose to self-glucosylates a tyrosine residue, creating a short primer of about 8 glucose residues. Glycogen synthase then extends this chain. Option A describes glycogen synthase. Option C describes branching enzyme. Option D is incorrect, as glycogenin has no kinase activity.
Reference: Lehninger Principles of Biochemistry, 8th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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