【生物课件】细胞质基质与细胞内膜系统

1.TheCompartmentalizationinEukaryoticCellsMembranesdividethecytoplasmofeukaryoticcellsintodistinctcompartments.

Threecategoriesineukaryoticcells:(1)theendomembranesystem:ER,Golgicomplex,Lys.,secretoryvesicles.(2)thecytosol.(3)mitochondria,chloroplasts,peroxisomes,andthenucleus.Membrane-boundstructures(organelles)arefoundinalleukaryoticcells.现在是1页\一共有62页\编辑于星期四CytoplasmicmatrixanditsfunctionsCytoplasmicMatrix:Theregionoffluidcontentofthecytoplasmoutsideofthemembranousorganelles.Aqueoussolutionoflargeandsmallmoleculesincludingfilamentsofcytoskeletonwhichactasorganizerforsomeorder.TheCytosolisthesiteofproteinsynthesisanddegradationormodification.Italsoperformsmostofthecell’sintermediarymetabolism.Cytoplasmicmatrix(Cytosol)andEndomembraneSystem现在是2页\一共有62页\编辑于星期四Functionsofcytoplasmicmatrix:Theproteinsynthesis,degradationandmodification.Cellscarefullymonitortheamountofmisfoldedproteins.Anaccumulationofmisfoldedproteinsinthecytosoltriggersaheat-shockresponse,whichstimulatesthetranscriptionofgenesencodingcytosolicchaperonesthathelptorefoldtheproteins.现在是3页\一共有62页\编辑于星期四现在是4页\一共有62页\编辑于星期四B.EndomembraneSystemEndomembraneSystem:ThestructuralandfunctionalrelationshiporganellesincludingER,Golgicomplex,lysosome,endosomes,secretoryvesicles.Membrane-boundstructures(organelles)arefoundinalleukaryoticcells.现在是5页\一共有62页\编辑于星期四Intracellularcompartment%oftotalcellvolumeCytosol54Mittchondria22RoughERcisternae9SmoothERcisternaeplusGolgicisternae6Nucleus6Peroxisome1Lysosomes1Endosomes1RelativevolumesoccupiedbythemajorintracellularcompartmentsinLiverCell现在是6页\一共有62页\编辑于星期四C.TheDynamicNatureoftheEndomembraneSystemMostorganellesarepartofadynamicsysteminwhichvesiclesmovebetweencompartments.Biosyntheticparthwaysmoveproteins,carbohydratesandlipidswithinthecell.Secretorypathwaysdischargeproteinsfromcells.Endocyticparthwaysmovematerialsintocells.Sortingsignalsarerecognizedbyreceptorsandtargetproteinstospecificsites.现在是7页\一共有62页\编辑于星期四D.Afewapproachestothestudyofcytomembranes

Insightsgainedfromautoradiography;Insightsgainedfromthebiochemicalanalysisofsubcellularfractions;Insightsgainedfromthestudyofgeneticmutants;Thedynamicactivitiesofendomembranesystemsarehighlyconserveddespitethestructuraldiversityofdifferentcelltypes.现在是8页\一共有62页\编辑于星期四DeDuve,A.ClaudeandG.Palade,1974NobelPlrize现在是9页\一共有62页\编辑于星期四2.ThestructureandfunctionsofEndoplasmicReticulum(ER)RoughendoplasmicreticulumandSmoothendoplasmicreticulum

RERhasribosomesonthecytosolicsideofcontinuous,flattenedsacs(cisternae);SERisaninterconnectingnetworkoftubularmembraneelements.现在是10页\一共有62页\编辑于星期四A.FunctionsoftherERProteinssynthesizedonribosomesofrERinclude:

secretoryproteins,integralmembraneproteins,solubleproteinsoforganelles.

现在是11页\一共有62页\编辑于星期四SynthesisofmembranelipidsMostmembranelipidsaresynthesizedenterlywithintheER.Therearetwoexceptions:sphingomyelinandglycolipids,(beginsinER;completedinGolgi);(2)someoftheuniquelipidsoftheMitandChlmembranes(themself).Themembranesofdifferent0rganelleshavemarkedlydifferentlipidscomposition.Transportbybudding：ER→GC、Ly、PMTransportbyphospholipidexchangeproteins(PEP)：ER→otherorganelles（includingMitandChl）现在是12页\一共有62页\编辑于星期四B.FunctionsofthesERSynthesisofsteroidsinendocrinecells.Detoxificationoforganiccompoundsinlivercells.Systemofoxygenases---cytochromep450familyReleaseofglucose6-phosphateinlivercells.SequestrationofCa2+.Ca2+-ATPase现在是13页\一共有62页\编辑于星期四3.ThestructureandfunctionsofGolgicomplexA.ThepolarityofGolgicomplex现在是14页\一共有62页\编辑于星期四a)CiscisternaeofGolgicomplex:reducedosmiumtetroxide(OsO4);b)ReactionforenzymemannosidaseII,localizedinthemedial;c)Reactionforenzymenucleosidediphosphatase,localizedinthetranscisternae.RegionaldifferencesinmembranecompositionacrosstheGolgistack现在是15页\一共有62页\编辑于星期四B.TheFunctionsofGolgicomplexGlycosylationintheGolgicomplexGolgicomplexplaysakeyroleintheassemblyofthecarbohydratecomponentofglycoproteinsandglycolipids.现在是16页\一共有62页\编辑于星期四ThecorecarbohydrateofN-linkedoligosaccharidesisassembledintherER.ModificationstoN-linkedoligosaccharidesarecompletedintheGolgicomplex.O-linkedoligosaccharidestakesplaceinGolgicomplex.现在是17页\一共有62页\编辑于星期四StructureoftypicalO-andN-linkedoligosaccharidesCoreRegionAfterR.KornfeldandS.Kornfeld,1985,Annu.Rev.Biochem.

45:631现在是18页\一共有62页\编辑于星期四Whatisthepurposeofglycosylation?N-linkedglycosylationisprevalentinalleucaryotes,butisabsentfromprocaryotes.Itdon’trequireatemplate.ThereisanimportantdifferencebetweentheconstructionofanoligosaccharideandthesynthesisofDNA,RNA,andprotein.Importantfunctions:

(1)Onemightsuspectthattheyfunctiontoaidfoldingandthetransportprocess;forexample,carbohydrateasamarkerduringproteinfoldinginERandtheuseofcarbohydrate-bindinglectinsinguidingER-to-Golgitransport.(2)Limittheapproachofothermacromoleculestotheproteinsurface,moreresistanttodigestionbyproteases.(3)Regulatoryrolesinsignalingthroughthecell-surfacereceptorNotch,toallowsthesecellstorespondselectivelytoactivatingstimuli.现在是19页\一共有62页\编辑于星期四TheGolginetworksareprocessingandsortingstationswhereproteinsaremodified,segregatedandthenshippedindifferentdirections.现在是20页\一共有62页\编辑于星期四

VesivulartransportwithintheGolgiapparatus:

Twoviews:cisternalmaturationmodelandvesiculartransportmodelTwopossiblemodelsexplainingtheorganizationoftheGolgicomplexandthetransportfromonecisternatothenext.现在是21页\一共有62页\编辑于星期四十

十

十

C.GolgiBiogenesisStagesofGolgigrowthanddivision.ShownarethinsectionelectronmicrographsofT.gondiiRHtachyzoitesreplicatingbyendodyogenyinHFFcells.CellswereplacedinoneoffourcategoriesaccordingtothenumberandsizeoftheGolgi:a,singleGolgi;b,single,elongatedGolgi;c,twoGolgi;d,Golgi,oftenmorevesiculated,ineachnascentdaughtercell,delineatedbythegrowinginnermembranecomplex(IMC).a,apicoplast;dg,densegranules;er,ER;es,ERexitsitesontheouterflattenedpartofthenuclearenvelope;G,Golgi;m,micronemes;mit,mitochondria;r,rhoptries.Scalebar,0.5mm.现在是22页\一共有62页\编辑于星期四StableexpressionofmammalianGolgiproteins.a,b,OverlaidimmunofluorescenceandphaseimagesofGRASP–YFP(a)andNAGTI–YFP(b)instable,transgeniccelllinesofToxoplasmagondii.c–h,ImmunofluorescenceimagesofatransgeniccelllineexpressingbothGRASP–CFP(green)andNAGTI–YFP(red)before(c–e)orafter(f–h)treatmentwith5mg/mlBFAfor10minat37ºC.Mergedimagesareshownontheright.AsterisksindicateasecretedformofNAGTI–YFPthataccumulatesintheparasitophorousvacuole.Scalebars,5mm.现在是23页\一共有62页\编辑于星期四Immunoelectronmicroscopyoftransgenicparasites.a–c,CryosectionsofGRASP–YFP(a,c)orNAGTI–YFP(b)transgenicparasites,pretreatedfor2hwith50mg/mlcycloheximide,beforebeingfixedandimmunolabelledforYFPusingpolyclonalantibodiesagainstGFPfollowedbyproteinAcoupledto5-nmgoldparticles.NotethehighdensityoflabellingrestrictedtoGolgimembranes.Inc,GRASP–YFPtransgenicparasitesweretreatedwithBFA(5mg/ml)for30minbeforeimmunolabelling.Notethetubulo-vesicularappearanceoftheGolgicausedbylossofGolgienzymestotheER.d,Quantificationofimagesinaandb.Resultsarepresentedasmean±s.d.goldparticles/um2.现在是24页\一共有62页\编辑于星期四BiogenesisoftheGolgiapparatusinlivingparasites.a–h,TransgenicparasitesstablyexpressingIMC1–CFP(blue)weretransfectedwithplasmidDNAencodingGRASP–YFP(green).After20hofinfectioninHFFs,fourparasiteswereimagedbytime-lapsevideofluorescencemicroscopy.Imagesweretakenevery10minfor7hat37°C.Representativeimagesattheindicatedtimesareshown.NotethatT.gondii.Replicatessynchronouslyinagivenvacuole,whichpermitssimultaneousimagingofseveralcellsatthesamecell-cyclestage.i,j,TransgenicparasitesexpressingNAGTI–YFP(green)wereimagedovertimeandsampleimageslateincelldivisionareshown.ForbothGolgimarkersnotetheinheritanceoftwostructuresbyeachnascentdaughter(f,i,j)andtheireventualcoalescence(arrowingandh).k,Threedimensionalreconstructionoftwoparasitesduringmitosis.TheGolgiwasselectivelyoutlinedinredandotherelectron-densestructureswerecolouredingreenordarkbluetodifferentiatethetwoformingdaughtercells.Golgiareinheritedbybothcells,andinthecompletereconstructionofonedaughter(right)twoGolgistructuresarevisible(arrows).NotethattheotherdaughterwasonlyreconstructedpartiallyandcontainsasingleGolgistructure.现在是25页\一共有62页\编辑于星期四4.ThestructureandfunctionsofLysosomesA.CharacteristicsofLysosomes①Lysosomeisaheterogenousorganelle:PrimarylysosomesSecondlysosomesheterophagicautophagicResidualbodyPrimaryLys.SecondLys现在是26页\一共有62页\编辑于星期四

Figure

6-19

Histochemicalvisualizationoflysosomes.

Electronmicro-graphsoftwosectionsofacellstainedtorevealthelocationofacidphosphatase,amarkerenzymeforlysosomes.Thelargermembrane-boundedorganelles,containingdenseprecipitatesofleadphosphate,arelysosomes,whosediversemorphologyreflectsvariationsintheamountandnatureofthematerialtheyaredigesting.Theprecipitatesareproducedwhentissuefixedwithglutaraldehydeisincubatedwithaphosphatasesubstrateinthepresenceofleadions.TwosmallvesiclesthoughttobecarryingacidhydrolasesfromtheGolgiapparatusareindicatedbyredarrowsinthetoppanel.(CourtesyofDanielS.Friend.)

现在是27页\一共有62页\编辑于星期四②Lysosomescontainplentyacidhydrolasesthatcandigesteverykindofbiologicalmolecule.---theprincipalsitesofintracellulardigestion.Markerenzyme:acidphosphatase③Lysosomemembrane:H+-pumps:internalprotonconcentrationiskepthighbyH+-ATPaseGlycosylatedproteins:mayprotectthelysosomefromself-digestion.

Transportproteins:transportingdigestedmaterials.现在是28页\一共有62页\编辑于星期四Figure

13-18

ThelowpHinlysosomesandendosomes.

ProteinslabeledwithapH-sensitivefluorescentprobe(fluorescein)andthenendocytosedbycellscanbeusedtomeasurethepHinendosomesandlysosomes.ThedifferentcolorsreflectthepHthatthefluorescentprobeencountersintheseorganelles.ThepHinlysosomes(red)isabout5,whilethepHinvarioustypesofendosomes(blueandgreen)rangesfrom5.5to6.5.(CourtesyofFredMaxfieldandKennethDunn.)现在是29页\一共有62页\编辑于星期四Figure

13-20

Theplantcellvacuole.

Thiselectronmicrographofcellsinayoungtobaccoleafshowsthatthecytosolisconfinedbytheenormousvacuoletoathinlayer,containingchloroplasts,pressedagainstthecellwall.Themembraneofthevacuoleiscalledthetonoplast.(CourtesyofJ.Burgess.)现在是30页\一共有62页\编辑于星期四B.TheFunctionsofLysosomesLysosomesareinvolvedinthreemajorcellfunctions:①phagocytosis;②autophagy;③endocytosis.Primarylysfusewitheitherphagocyticorautophagicvesicles,formingresidualbodiesthateitherundergoexocytosisorareretainedinthecellaslipofuscingranules.现在是31页\一共有62页\编辑于星期四C.LysosomesandDiseasesDisordersresultingfromdefectsinlysosomalfunction:①Autolysis:Abreakorleakinthemembraneoflysreleasesdigestiveenzymesintothecellwhichdamagesthesurroundingtissues(Silicosis).②

Lysosomalstoragediseasesareduetotheabsenceofoneormorelysosomalenzymes,andresultinginaccumulationofmaterialinlysosomesaslargeinclusions.OneseveretypeofthediseaseisI-celldisease(inclusion–celldisease,GlcNAc-Phosphotransferasegenemutant).

Tay-Sachsdiseaseresultsfromadeficiencyoftheenzyme(-N-hexosaminidaseA)whosefunctionistodegradegangliosides,amajorcomponentofbraincellmembranes.现在是32页\一共有62页\编辑于星期四表1.神经鞘脂贮积病疾病缺失酶类主要贮积底物后果GM1神经节苷脂贮积症GM1-半乳糖苷酶神经节苷脂GM1智力迟钝，肝脏肥大，骨骼受累，2岁前死亡泰－萨二氏病己糖胺酶A神经节苷脂GM2智力迟钝，失明，3岁前死亡法布莱氏病-半乳糖苷酶A三己糖神经酰胺皮疹，肾功能丧失，下肢疼痛山霍夫氏病己糖胺酶A和B神经节苷脂GM2和红细胞糖苷酯与泰－萨氏疾病症状相似，但发展更快高歇氏病葡糖脑苷酯酶葡糖脑苷脂肝脏和脾脏肿大，长骨腐蚀，只在婴儿期发生智力迟钝尼-皮二氏病鞘磷脂水解酶鞘磷脂肝脏和脾脏肿大，智力迟钝Farber’s脂肪肉芽肿病神经酰胺水解酶神经酰胺疼痛性与退行性的关节变形，皮肤瘤，几年内死亡Krabbe’s病半乳糖脑苷酯酶半乳糖脑苷脂髓磷脂缺失，智力迟钝，2岁前死亡脑硫脂沉积芳基硫酸酯酶脑硫脂智力迟钝，前十年死亡现在是33页\一共有62页\编辑于星期四D.BiogenesisofLysosomesFigure

6-23

Thetransportofnewlysynthesizedlysosomalhydrolasestolysosomes.

Theprecursorsoflysosomalhydrolasesarecovalentlymodifiedbytheadditionofmannose6-phosphateintheCGN.TheythenbecomesegregatedfromallothertypesofproteinsintheTGNbecauseaspecificclassoftransportvesiclesbuddingfromtheTGNconcentratesmannose6-phosphate-specificreceptors,whichbindthemodifiedlysosomalhydrolases.Thesevesiclessubsequentlyfusewithlateendosomes.AtthelowpHofthelateendosomethehydrolasesdissociatefromthereceptors,whicharerecycledtotheGolgiapparatusforfurtherroundsoftransport.Inlateendosomesthephosphateisremovedfromthemannoseonthehydrolases,furtherensuringthatthehydrolasesdonotreturntotheGolgiapparatuswiththereceptor.现在是34页\一共有62页\编辑于星期四Mannose6-phosphateresiduestargetproteinstolysosomesTargetingofsolublelysosomalenzymestoendosomesandlysosomesbyM-6-Ptag现在是35页\一共有62页\编辑于星期四

PhosphorylationofmannoseresiduesonlysosomalenzymescatalyzedbytwoenzymesRecognitionsitebindstoSignalpatchGlcNAcphosphotransferasephosphodiesterase现在是36页\一共有62页\编辑于星期四Figure6-40.Themannose6-phosphate(M6P)pathway,themajorroutefortargetinglysosomalenzymestolysosomes.

PrecursorsoflysosomalenzymesmigratefromtherERtothecis-Golgiwheremannoseresiduesarephosphorylated.IntheTGN,thephosphorylatedenzymesbindtoM6Preceptors,whichdirecttheenzymesintovesiclescoatedwiththeclathrin.Theclathrinlatticesurroundingthesevesiclesisrapidlydepolymerizedtoitssubunits,andtheuncoatedtransportvesiclesfusewithlateendosomes.Withinthislow-pHcompartment,thephosphorylatedenzymesdissociatefromtheM6Preceptorsandthenaredephosphorylated.ThereceptorsrecyclebacktotheGolgi,andtheenzymesareincorporatedintoadifferenttransportvesiclethatbudsfromthelateendosomeandsoonfuseswithalysosome.ThesortingoflysosomalenzymesfromsecretoryproteinsthusoccursintheTGN,andthesetwoclassesofproteinsareincorporatedintodifferentvesicles,whichtakedifferentroutesaftertheybudfromtheGolgi.[G.Griffithsetal.,Cell

52:329;S.Kornfeld,Annu.Rev.Biochem.

61:307;andG.GriffithsandJ.Gruenberg,TrendsCellBiol.

1:5]现在是37页\一共有62页\编辑于星期四5.ProteinSorting

Overviewofsortingofnuclear-encodedproteinsineukaryoticcellsProteinsareimportedintoorganellesbythreemechanisms:GatedTransport:TransportthroughnuclearporesTransmembranetransport:ER,Mit,Chl,PerVesiculartransport:ER-Golgi-PM-Lys,Endosome现在是38页\一共有62页\编辑于星期四

Roadmapofproteinsorting

现在是39页\一共有62页\编辑于星期四Proteinsorting:Proteinmoleculesmovefromthecytosoltotheirtargetorganellesorcellsurfacedirectedbythesortingsignalsintheproteins.现在是40页\一共有62页\编辑于星期四SignalpeptidesandSignalpatchesFigure

6-8

Twowaysthatasortingsignalcanbebuiltintoaprotein.

(A)Thesignalresidesinasinglediscretestretchofaminoacidsequence,calledasignalpeptide,thatisexposedinthefoldedprotein.Signalpeptidesoftenoccurattheendofthepolypeptidechain,buttheycanalsobelocatedelsewhere.(B)Asignalpatchcanbeformedbythejuxtapositionofaminoacidsfromregionsthatarephysicallyseparatedbeforetheproteinfolds;alternatively,separatepatchesonthesurfaceofthefoldedproteinthatarespacedafixeddistanceapartcouldformthesignal.现在是41页\一共有62页\编辑于星期四Gatedtransport:

Throughgatedpores—Nuclearpores;Nuclearlocalizationsignal(NLS);Foldedandassemblyformtotransport.TransmembranetransportERsignalsequence,Mit,Chl,Per:Leadersequence;Throughtranslocononthemembrane;SingleandUnfoldform;Helpedbymolecularchaperons现在是42页\一共有62页\编辑于星期四VesiculartransportBudding,transporting,dockingandatlastfusionwithtargetmembrane;Assemblycoatedproteinsonthevesicles(Clathrin,COPIIandCOPI);OnlyProperlyfoldedandassembledproteins;Theorientationoftransportedproteinsandlipidsisnotchangedduringtransporting.现在是43页\一共有62页\编辑于星期四B.SignalHypothesis

--G.Blobel&D.Sabatini,1971.AmodelfortheSignalMechanismofCotranslationalImportEvidenceThatProteinSynthesizedonRibosomesAttachedtoERMembranesPassDirectlyintotheERLumen(D.Sabatini)Milstein:IgG现在是44页\一共有62页\编辑于星期四Milsteinetal:StudyingthesynthesisoflightchainofIgG(incell-freesystems,20AalongeratN-terminalendthantheauthenticlightchain)AddingERmembranestothissystemleadstotheproductionofanIgGlightchainofthecorrectsize.现在是45页\一共有62页\编辑于星期四

ASchematicmodelforthesynthesisofasecretoryproteinonamembrane-boundribosomeoftheroughER现在是46页\一共有62页\编辑于星期四Signal-recognitionparticle,SRP:Sixdifferentpolypeptidescomplexedwitha300-nucleotide(7S)moleculeofRNA.ERsignalsequence:Typically15-30aminoacids:Consistofthreedomains:apositivelychargedN-terminalregion,acentralhydrophobicregion,andapolarregionadjoiningthesitewherecleavagefromthematureproteinwilltakeplace.AsignalsequenceonnascentseretoryproteinstargetsthemtotheERandisthencleavedoffSRPreceptor(GTPbindingprotein)SRPhavethreemainactivesites:OnethatrecognizesandbindstoERsignalsequence;Onethatinteractswiththeribosometoblockfurthertranslation;OnethatbindstotheERmembrane(dockingprotein))现在是47页\一共有62页\编辑于星期四ThesortingsignalofVSVglycoproteins:Asp-X-Gln或DXEFigure6-43.Thesortingofproteinsdestinedfortheapicalandbasolateralplasmamembranesofepithelialcells.

WhenculturedMDCKcellsareinfectedsimultaneouslywithVSVandinfluenzavirus,theVSVglycoproteinisfoundonlyonthebasolateralmembrane,whereastheHAglycoproteinoftheinfluenzavirusisfoundonlyontheapicalmembrane.Liketheseviralproteins,somecellularproteinsaresorteddirectlytotheapicalmembraneandotherstothebasolateralmembraneviaspecifictransportvesiclesthatbudfromthetrans-Golginetwork.Incertainotherpolarizedcells,someapicalandbasolateralproteinsaretransportedtogethertothebasolateralsurface;theapicalproteinsthenmoveselectively,byendocytosisandtranscytosis,totheapicalmembrane.[K.Simonsetal.,Cell

62:207;K.Mostovetal.,JCB.

116:577]现在是48页\一共有62页\编辑于星期四Start-transferSequence&Stop-transferSequence现在是49页\一共有62页\编辑于星期四Figure6-24.SynthesisandinsertionintotheERmembraneoftheGLUT1glucosetransporterandotherproteinswithmultipletransmembranea-helicalsegments.

TheN-terminalahelixfunctionsasaninternal,uncleavedsignal-anchorsequence(red),directingbindingofthenascentpolypeptidechaintotherERmembraneandinitiatingcotranslationalinsertion.BothSRPandtheSRPreceptorareinvolvedinthisstep.Followingsynthesisofhelix2,whichfunctionsasastop-transfermembrane-anchorsequence,extrusionofthechainthroughthetransloconintotheERlumenceases.ThefirsttwoahelicesthenmoveoutofthetransloconintotheERbilayer,anchoringthenascentchainasana-helicalhairpin.TheC-terminusofthenascentchaincontinuestogrowinthecytosol.Subsequenta-helicalhairpinscouldinsertsimilarly,althoughSRPandtheSRPreceptorarerequiredonlyforinsertionofthefirstsignalanchorsequence.Althoughonlysixtransmembraneahelicesaredepictedhere,GLUT1andproteinsofsimilarstructurehavetwelveormore.[H.P.Wesselsetal.,Cell

55:61.]现在是50页\一共有62页\编辑于星期四TheOrientationofNascentPolypeptide

TheNascentpolypeptideisorientedwithintransloconsothatthepositivelychargedflankingsequencefacesthecytosol现在是51页\一共有62页\编辑于星期四C.

AModelforthePostranslationalImportofPolypeptidesintotheMit.Post-translationalmodificationandqualitycontrolintherERDisulfidebondsareformedandrearrangedintheERlumenOnlyinERlumenistherearedoxenvironmentforoxidationof–SHgroups.PDI:proteindisulfideisomerase,foundinabundanceintheERlumen现在是52页\一共有62页\编辑于星期四6.

TypesofVesicleTransportandTheirFunctionsA.Thethreedifferenttypesofcoatedvesicles.Differentcoatproteinsselectdifferentcargoandshapethetransportvesiclesthatmediatethevariousstepsinthebiosynthetic-secretoryandendocyticpathways.现在是53页\一共有62页\编辑于星期四COPII-coatedvesiclesmovematerialsfromtheERtotheGolgi.TheassemblyofaCOPII-coatedvesicles.Sar—GTPbindingprotein:Sar-GTPbindstotheER;Sar-GDPdissociatesfromtheERAntibodiesisabletoblockthebuddingofvesiclefromERbuthavenoeffectonvesicletransportfromoneGolgicompartmenttoanotherinmammaliancell.现在是54页\一共有62页\编辑于星期四COPI-coatedvasiclestransportingEscapedERresidentProteinsBacktotheER.TheassemblyofaCOPI-coatismediatedbyADP-ribosylationfactor(ARF),GTPbindingprotein,whichisrequiredforvesicletransferbetweencisternae.COPIcoatedvesiclesmayselectspecificcargo.

ERisanopenprison.SolubleERproteinbearRetrievingsignal—KDEL(Lys-Asp-Glu-Leu)inmammalandHDELinyeast,whereasERmembraneproteinsbearthesignalKKXX.TheKDELreceptorpresentinvesiculartubularclustersandtheGolgiapparatus..(3)COPI-coatedvesiclewerefirstidentifiedbytreatmentofGTPanalogues---COPI-coatedvesicleaccumulatedwithinthecellandcouldbeisolatedbycentrifugation.现在是55页\一共有62页\编辑于星期四Clathrin-coatedvesicle:TransportingCargofromtheTGNtoendosomes,Lysosomes,andplantvacuolesandalsomovematerialsfromthePMtocytoplasmiccompartmentsalongtheendocyticpathway.TheTGNofGolgiistheSourseofClathrin-coatedvesicle.(2)Clathrin-coatscontain:

proteinclathrin-----whichformsastructuralscaffold,adaptors----multisubunit,whichformsaninnershell.

现在是56页\一共有62页\编辑于星期四B.TheSNAREHypothesisforTransportVesicleTargetingandFusionSpecificityinvesicledockingandfusionisthoughttobeattainedthroughspecificinteractionsbetweenspecificv-SNAREproteinsonthevesiclemembranesandt-SNAREproteinsonthemembranesofthetargetcompartment.SNAREsareaproteinfamily.Thereareatleast20differentSNAREsinananimalcell.TheroleofSNAREsinguidingvesiculartransport.现在是57页\一共有62页\编辑于星期四我劝一个草率结婚的朋友离婚。她平静的告诉我，如果说当初鲁莽结婚是个错误。那么，现在草率离婚是一错再错。这位朋友后来还是离婚了，大家一致认为她的行为很理性。

同样的故事正在互联网搜索巨头谷歌身上发生，但是谷歌选择了草率“离婚”。

饮鸩止渴

由于急于抑制苹果iphone手机翻天覆地的产业冲击，谷歌采取急功近利的粗糙型开放策略。饮鸩止渴的策略一时取得了成果。市场研究公司尼尔森最近公布的数据显示，在通过VerizonWireless、AT&T和SprintNextel三大运营商经销后，谷歌Android手机在美国市场上的销售量已经超过iPhone。另一家市场研究公司iSuppli甚至认为，全球范围内使用Android操作系统的手机数量将在2012年超过苹果iPhone。

表面繁华的背后，是Android生态系统的一团糟，谷歌正在为自己的粗放型开放策略买单。

用户对谷歌手机的态度从开始的好奇、后来的犹豫，变成强烈的批评。“大多Android手机程序都是垃圾，乱七八糟的”，一位手机发烧友迅速投奔了iphone的阵营：“同样的植物人大战僵尸游戏，在谷歌手机和iphone手机上的体验简直没法比”

混乱，还是混乱。一切一切的乱象，折射出谷歌已经失去对Android生态系统的控制。这一切的根源，我的判断是开放策略初期过于宽松，导致失去控制权。混乱的生态系统表现在用户手机上，就是应用程序的混乱和粗燥。

一错再错

为此，谷歌开始采取对策。最近，有国内厂商称新的Android3.0开始关闭应用程序的API(应用程序编程接口)，统一Android界面。这意味着，谷歌将放弃其初始开放策略，开始封闭管理。

粗看之下，谷歌认识到自己的错误。既然是过度开放导致的错误，那么收紧开放尺度是很自然的逻辑，无懈可击。但我认为，谷歌仓促收紧开放策略仍然是个错误。打个比喻。如果过度开放的政策是草率结婚，那么草率的封闭就是草率离婚。这么判断的原因很简单，谷歌把Android开放出去的那一天，Android已经不属于谷歌。谷歌没有认识到这一点，还以为Android只是自己的。

合作伙伴对谷歌封闭政策的反应加强了我的判断结论。经济观察报报道，国内第一家生产基于Android平台手机的设计公司创杨通信，近日已经被迫出售。创杨通信负责人给出的出售理由是，“因为不愿意甘当炮灰而选择放弃。”

按照目前Android3.0将统一界面的想法，未来的手机市场将出现毫无差异化的产品。这对于企业来说，几乎意味着不可避免的价格战。利润空间的微薄，导致合作伙伴生存环境恶劣。于是大量退出几乎是一种必然。

除了为合作伙伴找到新的利益空间，谷歌还将面临开放阵营精神层面的声讨，这对谷歌的挑战会更大。如果说谷歌为了自己竞争的私利利用了开放，赢得了名声。那么，谷歌不能一脚把开放踢开，他现在还需要为这种名声买单。

如果只顾自己收网，谷歌会被面临铺天盖地的道德谴责。谷歌，希望你准备好了，三思而行。

木桶效应就是指一个水桶无论有多高，它盛水的高度取决于其中最低的那块木板。这在选购手机的时候也同样适用。尤其是很多用户在购买手机的时候，都会专注于某一个参数，比如要求处理器主频要高达1GHz，但一部手机的整机表现是由多个因素组成，所以在购买手机的时候一定要从整体的角度上来看一部手机的性除了处理器主频以外，其实还有很多影响整机表现的元素，比如运行内存(RAM)、机身内存(ROM)、操作系统、厂商对系统的优化都会有所影响。不过在很多用户眼中，这几项却远没有处理器主频重要。而如果忽略这几项的话，可能买到一个主频很高，但整机性能却仍然不令人满意的机型。

用户在选机过程中切勿只关注一个硬件参数，这样很可能并不能买到一款理想的机型，就算买的手机主频再高，运行内存低的话仍然无法同时运行数个程序、机身内存小的话则无法把太多的软件安装到机器上，这对整机耗电和运行速度方面都有所影响、而厂商优化更是决定着一部手机的稳定性和部分运行速度。综上所述，大家在选购手机的时候一定要综合考虑一款手机的硬件规格。除此之外，也不要把硬件看的太过重要，就比如苹果iPhone3GS在硬件配置上并不出众，但却在操控手感以及软件资源上目前难有机型企及。更高分辨率能获得更为逼真细腻的显示效果，所以对于屏幕的分辨率绝大多数人都会偏向于分辨率更高的机型。但对于笔者所说的高分辨率未必是好事会有所怀疑。其实这里说的高分辨率“不好”更多是指采用非主流的高分辨率机型。在此前，就有几款“悲情”机型在分辨率上吃了不小的亏。

大名鼎鼎的HTCDiamond就是一款颇具代表意义的机型，Diamond上市的手机市场还处于QVGA时代、只有少数旗舰机皇采用WVGA这样级别的屏幕，由于HTCDiamond却采用了VGA这一过渡型的分辨率，而也正是因为这一点，Diamond很多软件都未有支持或无法完美运行，可谓是一个不小的遗憾。除此之外，曾经非常经典的

现在是58页\一共有62页\编辑于星期四附赠人生心语人生太短，聪明太晚人生太短，聪明太晚(1)

我们都老得太快

却聪明得太迟把钱省下来，等待退休后再去享受结果退休后，因为年纪大，身体差，行动不方便，哪里也去不成。钱存下来等养老，结果孩子长大了，要出国留学，要创业做生意，要花钱娶老婆，自己的退休金都被拗走了。人生太短，聪明太晚(2)

当自己有足够的能力善待自己时，就立刻去做，老年人有时候是无法做中年人或是青少年人可以做的事，年纪和健康就是一大因素。小孩子从小就告诉他，养你到高中，大学以后就要自立更生，要留学，创业，娶老婆，自己想办法，自己要留多一点钱，不要为了小孩子而活我们都老得太快却聪明得太迟，我的学长去年丧妻。这突如其来的事故，实在叫人难以接受，但是死亡的到来不总是如此。学长说他太太最希望他能送鲜花给他，但是他觉得太浪费，总推说等到下次再买，结果却是在她死后，用鲜花布置她的灵堂。这不