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Published byほのか とべ Modified over 5 years ago
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Function introduction to G proteins (more details in another lecture)
Small proteins, bind GDP & GTP GDP bound at rest GTP becomes bound when G protein is activated by receptor G proteins consist of 3 subunits, , , -GTP is the active subunit different families of G proteins exist
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At rest at rest, G protein has GDP bound inactive receptor
membrane receptor Effector eg adenylate cyclase G protein
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Agonist binding agonist binds to receptor causing a conformational change G protein becomes activated (ie binds GTP) R AC G Agonist GTP
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Activation of 2nd messenger
G protein diffuses in membrane and binds to enzymes present in membrane (eg adenylate cyclase, phospholipase C) and/or ion channels this activates or inactivates these enzymes or channels R AC GTP G active
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Summary G protein then breaks down GTP to GDP and is inactivated R AC
Agonist GTP R AC GTP G active R AC GDP G
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Function II G proteins can interact with different receptors and effectors overall effect depends on receptor and cell eg adrenaline on beta-adrenoreceptor in smooth muscle activates adenylate cyclase increases cAMP activates a protein kinase muscle relaxation G proteins produce amplification a single agonist/receptor complex can activate several G proteins in turn and each can activate enzymes etc
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