bis_104_insulin_syn_secretion_fall_08 - Ca channel opens 4...

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Insulin synthesis by pancreatic Beta-cells in islets of Langerhans 1. Pre-proinsulin (pro-insulin plus 23 amino acids of signal peptide) synthesized in RER of Beta-cells. 2. pro-insulin created when signal sequence is cleaved in the RER. 3. Pro-insulin packaged in Golgi and transported in vesicles to inner leaflet of PM; awaits signal to exocytose. Stimulation of insulin secretion 1. Elevated blood glucose enters Beta-cell via GLUT-2 uniporter. 2. In cytoplasm, glucose - glucose – 6 P - glycolysis-- ATP /ADP 3. ATP stimulates K + channel and, in turn, a voltage – gated
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Unformatted text preview: Ca ++ channel opens. 4. Ca ++ influx triggers fusion of insulin containing vesicle with Beta cell PM. 5. Insulin enters blood stream and interacts with any cells that have insulin receptors on PM. 6. Insulin binds to receptor ( RTK: receptor tyrosine kinase) e.g., on adipocytes and initiates signal cascade that causes activation of protein kinase B ( PKB). 7. PKB mobilizes stored GLUT – 4 uniporter to the PM and glucose uptake is facilitated. Glyconeogenesis increases Glycolysis decreases Amino acid uptake and protein synthesis increase...
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