Glycogenesis and Glycogenolysis Notes

Glycogenesis & Glycogenolysis

Learning Objectives

• Understand the processes of glycogen synthesis and breakdown.

Glycogen Synthesis and Degradation

• Glycogenesis: The process in which excess glucose is converted into glycogen, a polymer of glucose, for storage in muscles and liver. This process is crucial for maintaining energy levels in the body.
  • Three Steps of Glycogenesis:
  1. Isomerization: Conversion of glucose to glucose-6-phosphate (G6P) to prepare for activation.
  2. Activation: Glucose-6-phosphate is converted to glucose-1-phosphate, then activated by uridine triphosphate (UTP) to form uridine diphosphate glucose (UDP-glucose).
  3. Glucose Transfer: The activated UDP-glucose is transferred to a growing glycogen chain, facilitated by the enzyme glycogen synthase.

Glycogenolysis

• Glycogenolysis: The breakdown of glycogen into glucose, primarily occurring when blood glucose levels are low.
  • Products of Glycogenolysis:
  • Glucose-6-Phosphate (G6P): This molecule can enter the glycolysis pathway for energy production.
  • Free Glucose: Released into the bloodstream to supply energy to tissues such as the brain and muscles.

Regulation of Glycogenesis and Glycogenolysis

• Glycogen metabolism is intricately regulated by hormones, ensuring energy balance in the body:
  • Insulin:
  • Released when blood glucose levels are high.
  • Promotes glycolysis (the breakdown of glucose for energy) and stimulates glycogenesis (the formation of glycogen).
  • Glucagon:
  • Released when blood glucose levels are low.
  • Initiates glycogenolysis (the breakdown of glycogen) to release glucose.
  • Inhibits glycogenesis to prevent further glycogen formation during low glucose levels.