细胞内膜系统

Cellbiology

CellstructureCelllifeactivitiesBasicpropertiesMethodologyCellmembraneCytosolandEndoplasmsystem

CellEnergyNucleusandChromosomeCellProliferation

CellSignaling

celldifferentiationApoptosisintroductionCytoskeleton

CellJunctionandhesionCellmemberane’stransportChapter8CytosolandEndomembraneSystemSection1：CytosolSection2：EndomembraneSystemThepartofacellthatisenclosedwithintheplasmamembrane.Threemajorelements:thecytosol,inclusionsandorganelles.CytoplasmThefluidportioninsidethecellandoutsidethenucleus.Makesupabout70

%ofthecellvolume.CytosolWater:Mostofthecytosoliswater,whichmakesupabout70%ofatypicalcellbyvolume.

Ions:

cytosolhasahighconcentrationofpotassiumionsandalowconcentrationofsodiumionsMacromolecules:

Proteinmoleculesthatdonotbindtocellmembranesorthecytoskeletonwillbedissolvedinthecytosol.Theamountofproteinincellsisextremelyhigh,andapproaches200mg/ml,occupyingabout20-30%ofthevolumeofthecytosol.CompositionofCytosolTheconcentrationsoftheionsincytosolarequitedifferentfromthoseinextracellularfluidOrganizationoftheCytosolAlthoughthecomponentsofthecytosolarenotseparatedintoregionsbycellmembranes,thesecomponentsdonotalwaysmixrandomlyandseverallevelsoforganizationcanlocalizespecificmoleculestodefinedsiteswithinthecytosol.Proteincomplexes:

Proteinscanassociatetoformproteincomplexes.Awell-understoodexampleisthecarboxysome(羧酶体),whichcontainsenzymesinvolvedincarbonfixationsuchasRuBisCO(ribulosebisphosphatecarboxylase,核酮糖二磷酸羧化酶).OrganizationoftheCytosolProteinsintheCytosol20,000differentproteinsinatypicalmammaliancell½to2/3of20,000proteinsstayedincytosolwheretheyaresynthesizedProteinsthatdonotstayinthecytosolpassthroughamembranetobesecreted,tobemembraneprotein,ortransporttoothercompartments.Smallparticlesofinsolublesubstancessuspendedinthecytosol:Crystalsofcalciumoxalate(草酸钙)orsilicondioxideinplants(二氧化硅)Granules

ofenergy-storagematerialssuchasstarches(淀粉),glycogen（糖原）。Sphericaldroplets

offattyacidsandsterols（固醇）.CytoplasmicInclusions

FunctionsoftheCytosolItiswhereamajorpartofcellularmetabolism

takesplace;importantforglycolysis（醣酵解）

Proteinsynthesis,degradationandmodificationSignaltransductionMetabolismIneukaryotes,whilemanymetabolicpathwaysstilloccurinthecytosol,othersarecontainedwithinorganelles.Inprokaryotes,mostofthechemicalreactionsofmetabolismtakeplaceinthecytosol,whileafewtakeplaceinmembranesorintheperiplasmicspace.CytosolandEndomembraneSystemSection1：CytosolSection2：EndomembraneSystemAsystemofmembranesthroughwhichmaterialsaresequesteredfromthecytoplasmEndomembraneSystemEndoplasmicReticulum(ER)GolgiApparatusLysosomesVesiclesOuterNuclearEnvelopePlasmaMembraneEndomembraneSystemERGolgicomplexLysosomeAnextensivemembranenetworkofcisternae(潴泡)heldtogetherbythecytoskeleton,locatedinthecytoplasm.

TheStructureofERTheStructureofERThebasicstructureandcompositionoftheERmembraneissimilartotheplasmamembrane.RoughER(RER)SmoothER(SER)Aseriesoffoldedsheetsandinterlockingchannels.ThesurfaceofRERisstuddedwithprotein-manufacturingribosomesgivingita"rough"appearance.RERRERContinuouswiththenuclearmembrane.TheribosomesonlybindtotheERwhenitbeginstosynthesizeaproteindestinedforsorting.SERSERappearssmoothduetoalackofresidentribosomes.Consistsoftubulesandvesiclesthatbranchforminganetwork.InsomecellstherearedilatedareasliketheRER.ImagesofEREMFluorescentRERandSERSeparationbyCentrifugationSmoothmicrosomescomefromSER,plasmamembrane,Golgiapparatus,endosomesandmitochondria(exception:liver)FunctionsoftheRERProteinSynthesisGlycosylation（糖基化）ofSynthesizedProteinsProteinFoldingQualityControlProteinSynthesizeOnribosomesattachedtocytosolicsurfaceofRERProteinssecretedoutsidethecellIntegralmembraneproteinsSolubleproteinswithinER,Golgicomplex,lysosomes,endosomesOnfreeribosomes:Synthesizedproteinsisreleasedintothecytosol:EnzymesPeripheralproteinsforplasmamembranesProteinsfornucleusProteinsformitochondria,peroxisomesTheSignalHypothesis(1970s)ERsignalsequenceSignalpeptidaseSignalRecognitionParticle(SRP)ERsignalsequencesandSRPdirectribosomestotheERmembraneSignalSequenceisRemovedfromMostSolubleProteinsafterTranslocationFreeandMembrane-boundRibosomeFunctionsoftheRERProteinSynthesisGlycosylationofSynthesizedProteinProteinFoldingQualityControlAsparagine-linked(N-linked)PrecursorOligosaccharideConsensussequenceforN-linkedglycosylation:Asn(天冬酰胺)-X-Ser/Thr（丝氨酸/苏氨酸）Precursoroligosaccharide（寡糖）:14sugarsTheprecursoristhesameinplants,animals,andsingle-celleukaryotesGlycosylationofSynthesizedProteinFunctionsoftheRERProteinSynthesisGlycosylationofSynthesizedProteinProteinFoldingQualityControlProteinsRequiredforProperProteinFoldinginRERBipandcalnexin(钙联结蛋白，chaperones):thatrecognizeandbindtounfoldedormisfoldedproteinsandgivethemcorrectconformation;othersProteindisulfideisomerase(PDI)GT(glucosyl-transferase,monitoringenenzyme)recognizeunfoldedormisfoldedproteinsandaddsaglucosetotheendofoligo.ProteinFoldingintheRER新生肽的折叠组装：非还原性的内腔，易于二硫键形成；

蛋白二硫键异构酶（proteindisulfideisomerase，PDI）

切断二硫键，帮助新合成的蛋白重新形成二硫键并处于正确折叠的状态

结合蛋白（Bindingprotein，Bip，chaperone） 识别错误折叠的蛋白或未装配好的蛋白亚单位，并促进重新折叠与装配。FunctionsoftheRERProteinSynthesisGlycosylationofSynthesizedProteinProteinFoldingQualityControlCellscarefullymonitortheamountofmisfoldedproteins.Anaccumulationofmisfoldedproteinsinthecytosoltriggersaheat-shockresponse,whichstimulatesexpressionofcytosolicchaperonessuchashsp70andhsp60thathelptorefoldtheproteins;Misfoldedproteinswillbedegraded.QualityControlbyChaperonesChaperoneHsp70:ATPase;stabilizesunfoldingproteins;transportsacrossmembranesandproteolysis;associatedwithmisfoldedandunassembledproteinsHsp60:ATPase;promotesefficientfoldingMisfoldedProteinResponseFunctionsoftheSERSynthesisoflipid.Degradationanddetoxificationinconcertwithlysosomesandperoxisomes,carriedoutbycytochromes.Glycogenmetabolisminlivercells.RegulatesCa2+ionreleaseintocytosol–importantformusclecontraction.LipidsSynthesisintheSERMostlipidsincludingphospholipids,ceramideandsterolsaresynthesizedintheER.Therearetwoexceptions:Peroxisomescansynthesizecholesterolandotherlipidsbythemselves;SomeoftheuniquelipidsoftheMitchondriaandChloroplastmembranessynthesizedbythemselves.Themembranesofdifferentorganelleshavemarkedlydifferentlipidscomposition.BiosynthesisofPhospholipidsontheCytosolicLeafletoftheSERLipidSynthesis:

Symmetricand

AsymmetricDrugDetoxificationCytochromeP450s:useoxygenandNADPHtohydroxylatealotofsubstrates,includingsteroidanddrugs.CytochromeP450sresidentinthemembraneofSER.Hydroxylation(羟基化)increasesthesolubilityofhydrophobicdrugsandfacilitatedtheclearancefromthebodyGlucogenMetabolismTheSERcontainstheenzymeglucose-6-phosphatasewhichconvertsglucose-6-phosphatetoglucose,astepingluconeogenesis.EndomembraneSystemERGolgiComplexLysosomeTheGolgiComplexTheGolgicomplex(alsocalledGolgibodyorGolgiapparatus)isanorganellefoundinmosteukaryoticcells.Identifiedin1898bytheItalianphysicianCamilloGolgiandwasnamedafterhim.StructureofGolgiComplexComposedoffivetoeightmembrane-boundstacksknownascisternae,arrangedlikeastackofpancakes.Polarity:cisfacetowardsER,transfacetowardscellmembrane.StructureFeaturesCisface:vesiclesbudfromRERandmergeintofirstlayerofGolgicomplex.StructureFeaturesTransface:thefacefromwhichvesiclesleavetheGolgi.Thesevesiclesthenproceedtolatercompartmentssuchasthecellmembrane(orplasmamembrane),secretoryvesiclesorlateendosomes.StructureFeaturesThecisternaestackhasfivefunctionalregions:thecis-Golginetwork,cis-Golgi,medial-Golgi,trans-Golgi,andtrans-Golginetwork.RegionaldifferencesinmembranecompositionacrosstheGolgistack.ImagesofGolgiComplex

FunctionsofGolgiComplexModificationoftheproteinstransportedfromREROligosaccharideprocessing:Golgicomplexplaysakeyroleintheassemblyofthecarbohydratecomponentofglycoproteinsandglycolipids.Hydroxylationofaminoacidresidues.Proteinsortingstations:whereproteinsaresegregatedandthenshippedindifferentdirections.OligosaccharideProcessinginERandGolgi

ComplexWhatisthePurposeofGlycosylation?Aidfoldingandthetransportprocess:forexample,carbohydrateasamarkerduringproteinfoldinginERandtheuseofcarbohydrate-bindinglectinsinguidingER-to-Golgitransport.Limittheapproachofothermacromoleculestotheproteinsurface,moreresistanttodigestionbyproteases.Regulatoryrolesinsignalingthroughthecell-surfacereceptorNotch,toallowsthesecellstorespondselectivelytoactivatingstimuli.FunctionsofGolgiComplexVesiclesfromtheER(viathevesicular-tubularcluster)fusewiththecis-Golginetworkandsubsequentlyprogressthroughthestacktothetrans-Golginetwork,wheretheyarepackagedandsenttotherequireddestination.Eachregioncontainsdifferentenzymeswhichselectivelymodifythecontents.VesicularTraffickingPathways:Greenarrows:endocyticRedarrows:biosynthetic-secretoryBluearrows:retrievalVesicularTraffickingmovementofmolecules(proteins,lipids,neurotransmitters)fromdonortoacceptorcompartmentProteinSortingSecretoryPathways:ConstitutivesecretionTransportedfromsiteofsynthesisandsecretedcontinuouslyRegulatedsecretionMaterialstobesecretedarestoredinlarge,denselypacked,membrane-boundsecretoryversicleDischargedfollowingspecificstimulusSecretoryPathways

UseofDifferentCoatsinVesicularTrafficERretrievalsignals:KKXXinERmembranesproteins

KDELsequenceinsolubleERresidentproteinspHcontrolsaffinityofKDELreceptors-higheracidicontransendMembraneproteinsinGolgiandERhaveshorterTMdomainsTwoModelsofThroughGolgiParkinson’sDiseaseEndomembraneSystemERGolgiComplexLysosome1974NobelLaureateinMedicinefortheirdiscoveriesconcerningthestructuralandfunctionalorganizationofthecell.GeorgeE.Palade:showedhowinsecretorycellsthesecretoryproteins,producedbytheribosomesontheoutsideofthereticulumenterthespacebetweenitsmembranes,migratetoaspecialorganelle,theGolgicomplex,wheretheyarechangedtoaformsuitableforsecretion.ChristianDeDuve:DiscoveringlysosomeandperoxisomeLysosomeContainacidhydrolyticdigestiveenzymesmadeintheRER.Varyinshapeandsizefromcelltocell,from25nmto1um(40xsizevariation).VesiclesisformedbybuddingfromGolgicomplex.Functiontodegradeproteins,enzymes,etc..Thecells’garbagedisposalsystemTypesofLysosomesTypesofLysosomesPrimarylysosmes:amembraneboundedsacthatbudsfromtheGolgicomplex.Aprimarylysosomecontainsmanyenzymes(collectivelycalledacidhydrolases)thataresynthesizedontheRERandsortedintheGolgi.2.Secondarylysosomes:primarylysomesfusewithphagosomesorpinosomestobecomesecondarylysosomes.1.Intergralproteins:hydrogenionATPase(protonpumps)1)Involvedinanactivetransportprocesswherebyprotonsaretransportedintothelumenoflysosomefromthecytosolofthecell.2)TherelativelyhighconcentractionofprotonsinthelumenofthelysosomeresultsinapHofabout5.0Glycosylatedproteins:mayprotectthelysosomefromself-digestion.3.Transportproteins:transportingdigestedmaterials.ProteinsintheLysosomesEnzymesintheLysosomeDNaseandRNaseAcidproteasespolysaccharideandmucopolysaccharidedegradingenzymes

lipiddegradingenzymesAllenzymesfunctionbestinanacidicpH(5.0)TheFunctionsofLysosomesLysosomesareinvolvedinthreemajorcellfunctions:①phagocytosis②autophagy③endocytosis.Primarylysosomefusewitheitherphagocyticorautophagicvesicles,formingresidualbodiesthateitherundergoexocytosisorareretainedinthecellaslipofuscingranules.LysosomesandDiseasesDisordersresultingfromdefectsinlysosomalfunction:1)Autolysis:Abreakorleakinthemembraneoflysosomereleasesdigestiveenzymesintothecellwhichdamagesthesurroundingtissues(Silicosis).2)

Lysosomalstoragediseasesareduetotheabsenceofoneormorelysosomalenzymes,andresultinginaccumulationofmaterialinlysosomesaslargeinclusions.I-celldisease(inclusion–celldisease):GlcNAc-Phosphotransferasegenemutant3)Tay-Sachsdiseaseresultsfromadeficiencyoftheenzyme(-N-hexosaminidaseA)whosefunctionistodegradegangliosides,amajorcomponentofbraincellmembranes.Sortingtodifferentcompartmentsismediatedbysignalsinthecytosolicdomainsofthetransmembraneproteins,whicharerecognizedbyadaptorproteins(APs).AmongtheseAPsaretheheterotetramericAP1,AP2,AP3,andAP4complexesandthemonomericGGA1,GGA2,andGGA3proteinsHumanDiseaseswithProteinSortingRoadmapofproteinsortingPeroxisomesVesiclesthatcontaincrystallinecoreofoxidativeenzymes.0.1to1.0umindiamete