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Overview of Glycogenesis Process

Apr 30, 2025

Glycogenesis Lecture Notes

Introduction

  • Glycogenesis: Process of assembling glucose molecules into glycogen for storage.
  • Glycogen: Large branched polysaccharide made of glucose units.
    • Structure:
      • Linear chains connected by alpha-1,4-glycosidic bonds.
      • Branches connected by alpha-1,6-glycosidic bonds every 8-12 glucose residues.
    • Location: Found in the cytoplasm of liver and muscle cells.
    • Function: Allows rapid enzymatic access to glucose; quick release when needed.

Importance of Glycogenesis

  • Regulates blood glucose levels.
  • Maintains a reserve of readily available energy.
  • Most active when blood glucose levels are high, e.g., after a high-carb meal.

Steps of Glycogenesis

  1. Activation of Glucose

    • Glucose enters cell and is phosphorylated to glucose-6-phosphate (G6P).
    • Enzymes: Phosphorylation by hexokinase (muscle cells) or glucokinase (liver cells).
    • G6P is isomerized to glucose-1-phosphate (G1P).
    • G1P reacts with uridine triphosphate (UTP) to form UDP-glucose.
      • UDP-glucose: High-energy precursor for polymerization.

  2. Primer Formation by Glycogenin

    • Glycogen synthase requires an initial primer provided by glycogenin.
    • Glycogenin has auto-glycosylating ability, forming a small glycogen primer.

  3. Elongation by Glycogen Synthase

    • Glycogen synthase adds glucose units from UDP-glucose to glycogen chain, forming alpha-1,4-glycosidic bonds.
    • Activation in response to insulin, indicating higher energy state.

  4. Branching by the Branching Enzyme

    • Branching enzyme introduces branch points by cleaving an alpha-1,4 bond and forming an alpha-1,6 bond.
    • Branching enhances solubility and allows rapid synthesis/breakdown.

Conclusion

  • Glycogenesis is crucial for energy storage and maintaining glucose levels.
  • Enables efficient storage and mobilization of energy through the creation of a highly branched glycogen structure.

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