exam4answ - Name _ NetID_ Biochemistry 462b Exam IV...

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Name _______ NetID__________ 1 Biochemistry 462b Exam IV Wednesday May 9, 2007 _______ Page 2 _______Page 3 ______Page 4 ______Page 5 ______Page 6 ______Page 7 ______Page 8 ______Page 9 ______ Page 10 ______ Total
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Name _______ NetID__________ 2 1. (8 pts) G-protein coupled receptor (GPCR) systems have evolved complex mechanisms to stimulate or reduce the biological response to ligand binding. Which of the following describes events in these pathways that would reduce or desensitize the biological response? Place an "X" in the correct blanks. ______ epinephrine binding causes GTP to replace GDP on Gs α __x___ prolonged ligand binding causes a G-protein receptor kinase to phosphorylate the cytoplasmic domain of the receptor ______ the receptor is bound by an agonist __x___ β -arrestin binds to the phosphorylated GPCR __x___the receptor is bound by an antagonist ___x__ the β -arrestin-GPCR complex associates with clathrin and the cytoskeleton proteins causing internalization ______ hormone binding to a GPCR stimulates a Gsq protein to activate phospholipase C __x___ β -arrestin complexed with the β -adrenergic receptor activates cAMP phosphodiesterase 2. (7 pts) The cellular response to insulin causes changes in signaling pathways that regulate gene expression and metabolism. Listed below are individual steps in these pathways. Indicate whether the response is mainly required for the gene expression pathway (G), the metabolism pathway (M), or is a part of both pathways (G,M). __GM___ insulin binding to its receptor ___GM__ IRS tyrosine phosphorylation ___G__ Ras activation by GTP exchange
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Name _______ NetID__________ 3 __G__ Raf kinase activation ___G__ ERK phosphorylation _M___ phosphoinositide 3-kinase activation __M(G)__ protein kinase B (Akt) phosphorylation 3. (6 pts) In the 1950s, Earl W. Sutherland Jr. and his colleagues carried out pioneering experiments to elucidate the mechanism of action of epinephrine and glucagon. From your knowledge about this signaling pathway, interpret each of the experiments described below by answering the questions. a. Adding epinephrine to a homogenate of liver resulted in an increase in the activity of glycogen phosphorylase. However, if the homogenate was first centrifuged at a high speed, and epinephrine was added to the clear supernatant fraction that contains phosphorylase, no activation occurred. Why?
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exam4answ - Name _ NetID_ Biochemistry 462b Exam IV...

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