Action of Insulin

• Insulin


  A hormone that increases the uptake of glucose into target cells
• Target cells of insulin

  • Muscle cells
  • Fat storage cells
  • Adipose tissue
  • Liver cells
• All target cells have specific insulin receptors on their cell surface membranes
• Action of Insulin

  1. Insulin binds to specific receptors

  2. Stimulates addition of GLUT proteins

  3. Increases permeability to glucose

  4. GLUT proteins stored in vesicles

  5. Vesicles move to cell surface and fuse
• GLUT proteins

  Glucose transporter proteins that facilitate glucose uptake
• When blood glucose levels are low

  GLUT proteins are stored inside the cell in vesicles
• When insulin binds to surface receptors

  Vesicles move to the cell surface membrane and fuse
• Rate of facilitated diffusion of glucose into target cells increases as a result of the increase in GLUT proteins
• Glucokinase

  An enzyme activated by insulin that phosphorylates glucose, trapping it inside cells
• Glycogen synthase

  An enzyme activated by insulin that converts glucose to glycogen in a process known as Glycogenesis
• Glycogenesis

  Conversion of glucose to glycogen