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Psy137Endocrine System

Gene transcription slower response most changes they

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Gene transcription Slower response Most changes they produce 100-300ms and can have a long latency >12h
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GPCR
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G-Proteins Heterotrimeric G-proteins We will discuss 3 main types for GPCR Gs-G stimulatory Gi/o-G inhibitory Gq- G other Can be excitatory or inhibitory All G-proteins have 3 subunits which break into two functional units upon receptor activation Gβγ These two functional subunits can do different things Small molecular weight G protein Not GPCR but are associated with enzymatic receptor activation Act much like the alpha subunit of the heterotrimeric G- proteins & are activated by GTP Seem to function as molecular switches in the cell
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GPCR can affect processes via the alpha subunit and the beta-gamma subunit
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GPCR Intracellular Cascades Receptor binding by a ligand causes a conformation change which causes the alpha subunit of the G protein to be activated Gs & Gi/o activated alpha subunit affect the same membrane bound enzyme adenylyl cyclase (AC) Gs alpha stimulates AC and Gi/o alpha inhibits it The beta-gamma subunit when dissociated from the alpha subunit can affect ion channels directly AC catalyzes the conversion of ATP into cyclic 3, 5 adenosine monophosphate (cAMP) Gs receptor activation increases cAMP levels Gi/o receptor activation decreases cAMP levels
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Enzymatic activity and signaling e.g. phosphorylation of proteins Inactive Active Phosphorylation controls protein activity.
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GPCR Intracellular Cascades cAMP is the second messenger cAMP is enzymatically degraded by phosphodiesterases (PDEs) cAMP can activate cAMP dependent protein kinase A (PKA) & can affect ion channels directly Unbound PKA is inactive but when bound by cAMP (two molecules) it is activated PKA can phosphorylate proteins which can affect their activity PKA can phosphorylate ion channels, receptors, cytoskeletal proteins and nuclear transcription factors Protein phosphatases undo the actions of second messenger dependent protein kinases (i.e. PKA)
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Gs Intracellular Cascades Gs receptor ligand binding activates Gs protein alpha subunit Dissociates and activates AC AC increases cAMP cAMP increases PKA activity
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G i/o Intracellular Cascade Gi/o receptor ligand binding activates Gi/o protein alpha subunit Dissociates and inhibits AC AC decreases cAMP Less PKA activation
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Gs & Gi/o
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GPCR Intracellular Cascade Gq receptor activation induces activity of a membrane bound protein phospholipase C (PLC) Two major forms of PLC beta and gamma The beta PLC is activated via Gq receptor activation It is not known yet if the Gq alpha or Gq beta-gamma subunit is responsible for this activation PLC catalyzes the breakdown of phosphatidylinositol (PIP2) into two molecules which serve as second messengers Inositol triphosphate (IP3) & diacylglycerol (DAG) IP3 is recycled by successive dephosphorylation into inositol which is used to generate more PIP2 IP3 acts on the IP3 receptor which when activated releases Ca++ from intracellular storage sites such as the ER
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GPCR Intracellular Cascade Ca++ can serve as a third messenger affecting the activity of enzymes Ca++ can also work in conjunction with calmodulin to form Ca++/calmodulin-dependent protein kinase (CaM-kinase) CaM-kinase can:
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