Final Review

Final Review - Final Review G proteins Link an...

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Final Review G proteins Link an extracellular signal and an intracellular response Important class if signaling complexes Examples of G proteins Gs- stimulatory G protein Stimulates adenylyl cyclase Gi inhibitory G protein Inhibits adenylyl cyclase Golf-olfactory G protein Gt transducing, the G protein Figure-The functioning of a G protein-linked receptor Membrane receptor Over 1000 G protein coupled receptors (GPCRs) integral membrane protein with 7 alpha helical regions spanning the membrane (heptahelical) Amino terminus extracellular Carboxy terminus intracellular G protein couple receptors Activated by binding of a “first” messenger signal molecule Hormone Neurotransmitter Interacts with a G protein Heterotrimeric G protein 3 subunits labeled alpha, beta, and gamma Interacts with receptor occupied by a signaling molecule When activated interacts with an effector element Associated with the intracellular face of the plasma membrane Effector enzyme Produces an intracellular “second” messenger Adenylyl cyclase is an integral membrane protein Another example if an effector element Ion channel Controls movement of ions across the plasma membrane G proteins “switch” protein Either “on” or “off” Activated by occupied (activated receptor GDP is bound to the alpha subunits of the inactive G protein heterotrimer Inactive (“off”) Active (“on”) Activation of G protein An activated receptor interacts with th G protein GTP replaces GDP on the alpha subunit The G protein dissociates into alpha-GTP ad Beta gamma dimer
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The G protein dissociates in Activated G protein subunits Interacts with their target enzymes or ion channels Inactivating G proteins Turned “off” when an intrinsic GTPase activity if the alpha subunit hydrolyzes GTP to GDP Alpha-GDP and the beta gamma dimer G protein-coupled signaling Membrane receptor is activated by an extracellular signal G proteins transfers the extracellular signal into the intracellular compartment by interacting with a target Target enzyme produces an intracellular “second” messenger Second messengers cAMP (cyclic adenosine monophosphate Synthesized from ATP Activates an enzyme called protein kinase Calcium Adenylyl cyclase Produces cAMP The enzyme is modulated (positively and negatively) by different G proteins Intracellular cAMP levels go up or down Depends on the summation of all the positive and negative signals on that cells Signaling components Membrane receptor> G protein> adenylyl cyclase> cAMP> protein kinase A Protein kinase Enzyme which phosphorylates target proteins Covalent transfer of phosphate group form ATP ti specific amino acids of target protein Post-translational modification Phosphorylation Acts as an “on” or “off” switch for the target protein Protein kinase A Inactive kinase-4 subunits ( a tetramer) 2 regulatory subunits 2 catalytic subunits activating protein kinase A In the cytoplasm cAMP binds to the R subunit R2c2 dissociates into a R dimer and 2 c monomers
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This note was uploaded on 11/03/2011 for the course BIO 1201 taught by Professor Sibenaller during the Fall '10 term at LSU.

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Final Review - Final Review G proteins Link an...

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