Chapter 14 Signal-Transduction Pathways (2)

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1、CHAPTER14Signal-TransductionPathwaysPiH20"ON""OFF"GTPGDPpositionpositionGTPSignal-transductioncircuitsinbiologicalsystemshavemolecularon–offswitchesthat,likethoseinacomputerchip(above),transmitinformationGDPwhen“on.”Commonamongthesecircuitsarethoseinc

2、ludingGproteins(right),whichtransmitasignalwhenboundtoGTPandaresilentwhenboundtoGDP.[(Left)CourtesyofIntel.]Acellishighlyresponsivetospecificchemicalsinitsenvironment:itmayOUTLINEadjustitsmetabolismoraltergene-expressionpatternsonsensingtheirpresence.

3、Inmulticellularorganisms,thesechemicalsignalsarecrucialto14.1HeterotrimericGProteinscoordinatingphysiologicalresponses(Figure14.1).ThreeexamplesofTransmitSignalsandResetThemselvesmolecularsignalsthatstimulateaphysiologicalresponseareepinephrine(someti

4、mescalledadrenaline),insulin,andepidermalgrowthfactor(EGF).14.2InsulinSignaling:Whenamammalisthreatened,itsadrenalglandsreleasethehormonePhosphorylationCascadesepinephrine,whichstimulatesthemobilizationofenergystoresandleadstoAreCentraltoManyimprovedc

5、ardiacfunction.Afterafullmeal,thebcellsinthepancreasSignal-TransductionProcessesreleaseinsulin,whichstimulatesahostofphysiologicalresponses,includ-14.3EGFSignaling:ingtheuptakeofglucosefromthebloodstreamanditsstorageasglycogen.Signal-TransductionSyste

6、msThereleaseofEGFinresponsetoawoundstimulatesspecificcellstoArePoisedtoRespondgrowanddivide.Inallthesecases,thecellreceivesinformationthatacertainmoleculewithinitsenvironmentispresentabovesomethreshold14.4ManyElementsRecurwithconcentration.Thechainofe

7、ventsthatconvertsthemessage“thismole-VariationinDifferentculeispresent”intotheultimatephysiologicalresponseiscalledsignalSignal-TransductionPathwaystransduction.14.5DefectsinSignal-TransductionSignal-transductionpathwaysoftencomprisemanycomponentsandP

8、athwaysCanLeadtoCancerbranches.Theycanthusbeimmenselycomplicatedandconfusing.How-andOtherDiseasesever,thelogicofsignaltransductioncanberevealedbyexaminingthe401402EpinephrineInsulinEpidermalgrowthfactor(EGF)+++CHAPTER14Signal-TransductionPathw