Insulin Receptor

Pancreas is the endocrine organ that produces and releases insulin

Insulin Receptor Tyrosine kinase pathway Initiates a variety of cellular responses related to glucose metabolism,. Activates enzyme glycogen syntahase: converts glucose to glycogen. Increases the GLUT4 transporter in membrane Inhibits the breakdown of glucagon to glucose in the liver.

Kinase pathway: receptor binds hydrophilic ligand. Phosphorylation and activation of proteins.

Regulation of Glucose Uptake by Insulin Insulin stimulates increase in number of glucose transporters at membrane surface – Increase number of transporters increases diffusion rate – Driving force (phosphorylation) remains the same Low insulin levels decrease the number of glucose transporters at membrane surface – Portions of membrane with transporters endocytose, trapping the transport protein in a vesicle – Vesicle cannot refuse with membrane until insulin levels increase Diabetes Type I - Juvenile Diabetes - cannot make insulin – Autoimmune disease – Insulin-secreting pancreatic cells destroyed Type II - Adult Onset Diabetes - loss of ability to respond to insulin – Lack of membrane receptors for insulin – Therefore, cannot mobilize enough facilitative transport proteins to surface

When insulin is low in the blood, the transporter is moved into the cytoplasm.