A hormone that stimulates the uptake of glucose into skeletal muscle and fat cells in respond to a rise in blood glucose.
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Madhur L.
In response to an increase in the glucose, the pancreas releases insulin into the bloodstream. What is the effect of insulin on adipocytes (fat cells) and muscle cells? Insulin will inhibit the GLUT4 glucose uniport found in these cells, thus decreasing glucose uptake. Insulin will activate the glucose-Na+ symport found in the plasma membrane of these cells, thus increasing the uptake of glucose. Insulin will trigger the fusion of vesicles containing glucagon with the plasma membrane of these cells, thus causing the secretion of glucagon into the bloodstream. Insulin will trigger the fusion of vesicles containing the GLUT4 glucose uniport with the plasma membrane of these cells, thus increasing the number of GLUT4 proteins in the plasma membrane.
Sri K.
Insulin is a hormone synthesized by the beta cells of the pancreas and is responsible for your cell's uptake of glucose from the blood. Therefore, in the presence of insulin, your blood glucose levels should drop as the glucose is moved into your cells. You should remember from our lectures on membrane transport that glucose is transported utilizing a glucose transporter. If you need a refresher, it is in Ch 12 or take a look at page 390 in your textbook. The human insulin receptor is an RTK receptor. When insulin binds, the dimerized RTKs will phosphorylate each other forming the binding sites on the tails. Insulin receptor substrate 1 (IRS-1) binds to one of these docking sites and is activated. Activated IRS-1 binds to and activates phosphoinositide 3-kinase (PI 3-kinase). PI 3-kinase activates Akt through the process discussed in our last lecture. One of the downstream effects of Akt is to cause the translocation of vesicles containing a glucose transporter to the cell membrane utilizing SNARE proteins to allow for fusion. The other downstream effect of Akt is that it phosphorylates and inhibits the enzyme glycogen synthase kinase, which inhibits the enzyme glycogen synthase. These intracellular effects will have the effect of lowering your blood glucose levels as you move glucose into the cell and synthesize glycogen. Diagram this pathway. Include all components that are highlighted. You may need to review membrane transport for some of it. Make sure to include the steps to activating Akt as well.
Josee P.
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