Lecture Notes on Glycogenesis

Introduction

• Glycogenesis: The synthesis of glycogen
• Primary cells involved: Liver and Muscles
  • Liver stores approx. 100 grams of glycogen
  • Muscles store approx. 300-400 grams of glycogen

Process Timing

• Occurs during the Fed state (absorptive state)
  • When blood glucose levels are high (hyperglycemia)
  • Not pathological; normal range is 80-120 mg/dL

Key Hormones

• Insulin: Produced by pancreas, regulates glycogenesis

Glycogenesis Process

1. Glucose Transport into Cells

   • Liver: GLUT2 transporter
   • Muscles: GLUT4 transporter

2. Phosphorylation of Glucose

   • Enzymes:
     • Liver: Glucokinase
     • Muscles: Hexokinase
   • Converts glucose to Glucose-6-Phosphate

3. Isomerization

   • Enzyme: Phosphoglucomutase
   • Converts Glucose-6-Phosphate to Glucose-1-Phosphate

4. Activation by Uridine Triphosphate (UTP)

   • Formation of UDP-Glucose
   • Coupling reaction releases energy by breaking pyrophosphate bonds
   • Enzyme involved: Pyrophosphatase

5. Formation of Primer

   • Glycogenin: Protein that initiates glycogen synthesis
   • Process of Auto-glycosylation
   • Formation of initial alpha-1,4-glycosidic bonds

6. Polymerization by Glycogen Synthase

   • Adds more glucose units, forming alpha-1,4-glycosidic bonds
   • Releases UDP

7. Branch Formation

   • Enzyme: Branching Enzyme
   • Breaks alpha-1,4-bonds and forms alpha-1,6-glycosidic bonds
   • Increases surface area without occupying entire cell

Summary

• Glycogen synthesized through a series of enzyme-catalyzed steps
• Involves phosphorylation, isomerization, and polymerization
• Utilizes insulin regulation and special enzymes for branching

Next Steps

• Future focus on Glycogenolysis: Breakdown of glycogen