bis_104_pq_29_ans_ss_i_2009 - Increased numbers of GLUT-4...

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BIS 104 PQ 29 ANS SS I 2009 29. a. When blood glucose levels rise, the pancreas is stimulated to secrete insulin. Describe how insulin interacts with fat and muscle cells to lower blood glucose levels. Insulin binds to transmemrane insulin receptors in the PM of fat and muscle cells. These receptors are RTKs that respond to insulin by undergoing a conformational change that activates their cytoplasmic tyrosine kinase domain. This sets off a cascade of phosphorylation events that lead to activation of protein kinase B (PKB). PKB stimulates the movement of cytoplasmic GLUT-4 receptors from the cytoplasm to the PM.
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Unformatted text preview: Increased numbers of GLUT-4 receptors transport glucose from blood into the ell where it is rapidly phosphorylated to maintain the glucose concentration gradient. b. At what point do voltage-gated ion channel proteins play a role in this process? Pancreatic beta cells respond to elevated blood glucose by closing potassium channels. This causes a shift in PM transmembrane potential which opens voltage-gated Ca++ channels. A transient rise in cytoplsmic free calcium is required for fusion of insulin containing vesicles with the beta cell PM (exocytosis = secretion of insulin)....
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