Lec26 - Lecture 26 Signal Transduction 2 A G...

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Lecture 26 Signal Transduction 2 A. G protein-coupled receptors (GPCRs) B. Tyrosine kinase-linked receptors C. Receptors with intrinsic kinase activity Lodish 6th ed. Chapters 15 and 16 L.5th edition Chapt. 13-14
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A. G protein-coupled receptors (GPCRs) Large receptor family: Light-activated receptors (rhodopsins) Thousands of odorant receptors Receptors for many hormones and neurotransmitters All GPCRs mediate a similar signaling pathway: Trimeric G proteins (a class of “GTPase switch proteins” ) stimulate or inhibit Effector enzymes which produce second messengers . α β γ Effector enzyme Second messengers (cAMP, diacylglycerol & inositol triphosphates) PK inactive Trimeric G protein ligand GPCR PK active Phosphorylation of target proteins exterior cytosol Cellular responses Stimulatory Gs protein Gs α + G β + G γ (stimultes adenylyl cyclase) Inhibitory Gi protein Gi α + G β + G γ (inhibits adenylyl cyclase) Stimulatory Gq protein Gq α + G β + G γ (stimulates phopholipase C) Plasma membrane
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All G protein-coupled receptors (GPCRs) have seven transmembrane regions ( α helices)
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Ligand-induced activation of GPCRs and associated effector enzymes Lodish 6th ed. Fig. 15-13
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Distinct G proteins (Gs & Gi) can either stimulate or inhibit effector enzymes Gs Gi Plasma membrane (adrenaline) Lodish 6th ed. Fig. 15-21
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See also Lodish 6th ed. Fig. 15-23
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PKA cAMP adrenaline glucagon GPCR (Liver &Muscle) GPCR (Liver) Gs protein Adenylyl cyclase Active Glycogen Phosphorylase Kinase (GPK) Active Glycogen Phosphorylase (GP) Activated PKA stimulates glycogen breakdown (Liver & Muscle) Fast cellular response Stress hypoglycemia (adrenal gland) (pancreas) Liver: Release of glucose Muscle: use of glucose for energy production (ATP) (see also Lodish 6th ed. Fig. 15-25)
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