【生物課件】細胞質基質與細胞內膜系統(tǒng)

1.TheCompartmentalizationinEukaryoticCellsMembranesdividethecytoplasmofeukaryoticcellsintodistinctcompartments.

Threecategoriesineukaryoticcells:(1)theendomembranesystem:ER,Golgicomplex,Lys.,secretoryvesicles.(2)thecytosol.(3)mitochondria,chloroplasts,peroxisomes,andthenucleus.Membrane-boundstructures(organelles)arefoundinalleukaryoticcells.當前第1頁\共有62頁\編于星期五\17點CytoplasmicmatrixanditsfunctionsCytoplasmicMatrix:Theregionoffluidcontentofthecytoplasmoutsideofthemembranousorganelles.Aqueoussolutionoflargeandsmallmoleculesincludingfilamentsofcytoskeletonwhichactasorganizerforsomeorder.TheCytosolisthesiteofproteinsynthesisanddegradationormodification.Italsoperformsmostofthecell’sintermediarymetabolism.Cytoplasmicmatrix(Cytosol)andEndomembraneSystem當前第2頁\共有62頁\編于星期五\17點Functionsofcytoplasmicmatrix:Theproteinsynthesis,degradationandmodification.Cellscarefullymonitortheamountofmisfoldedproteins.Anaccumulationofmisfoldedproteinsinthecytosoltriggersaheat-shockresponse,whichstimulatesthetranscriptionofgenesencodingcytosolicchaperonesthathelptorefoldtheproteins.當前第3頁\共有62頁\編于星期五\17點當前第4頁\共有62頁\編于星期五\17點B.EndomembraneSystemEndomembraneSystem:ThestructuralandfunctionalrelationshiporganellesincludingER,Golgicomplex,lysosome,endosomes,secretoryvesicles.Membrane-boundstructures(organelles)arefoundinalleukaryoticcells.當前第5頁\共有62頁\編于星期五\17點Intracellularcompartment%oftotalcellvolumeCytosol54Mittchondria22RoughERcisternae9SmoothERcisternaeplusGolgicisternae6Nucleus6Peroxisome1Lysosomes1Endosomes1RelativevolumesoccupiedbythemajorintracellularcompartmentsinLiverCell當前第6頁\共有62頁\編于星期五\17點C.TheDynamicNatureoftheEndomembraneSystemMostorganellesarepartofadynamicsysteminwhichvesiclesmovebetweencompartments.Biosyntheticparthwaysmoveproteins,carbohydratesandlipidswithinthecell.Secretorypathwaysdischargeproteinsfromcells.Endocyticparthwaysmovematerialsintocells.Sortingsignalsarerecognizedbyreceptorsandtargetproteinstospecificsites.當前第7頁\共有62頁\編于星期五\17點D.Afewapproachestothestudyofcytomembranes

Insightsgainedfromautoradiography;Insightsgainedfromthebiochemicalanalysisofsubcellularfractions;Insightsgainedfromthestudyofgeneticmutants;Thedynamicactivitiesofendomembranesystemsarehighlyconserveddespitethestructuraldiversityofdifferentcelltypes.當前第8頁\共有62頁\編于星期五\17點DeDuve,A.ClaudeandG.Palade,1974NobelPlrize當前第9頁\共有62頁\編于星期五\17點2.ThestructureandfunctionsofEndoplasmicReticulum(ER)RoughendoplasmicreticulumandSmoothendoplasmicreticulum

RERhasribosomesonthecytosolicsideofcontinuous,flattenedsacs(cisternae);SERisaninterconnectingnetworkoftubularmembraneelements.當前第10頁\共有62頁\編于星期五\17點A.FunctionsoftherERProteinssynthesizedonribosomesofrERinclude:

secretoryproteins,integralmembraneproteins,solubleproteinsoforganelles.

當前第11頁\共有62頁\編于星期五\17點SynthesisofmembranelipidsMostmembranelipidsaresynthesizedenterlywithintheER.Therearetwoexceptions:sphingomyelinandglycolipids,(beginsinER;completedinGolgi);(2)someoftheuniquelipidsoftheMitandChlmembranes(themself).Themembranesofdifferent0rganelleshavemarkedlydifferentlipidscomposition.Transportbybudding：ER→GC、Ly、PMTransportbyphospholipidexchangeproteins(PEP)：ER→otherorganelles（includingMitandChl）當前第12頁\共有62頁\編于星期五\17點B.FunctionsofthesERSynthesisofsteroidsinendocrinecells.Detoxificationoforganiccompoundsinlivercells.Systemofoxygenases---cytochromep450familyReleaseofglucose6-phosphateinlivercells.SequestrationofCa2+.Ca2+-ATPase當前第13頁\共有62頁\編于星期五\17點3.ThestructureandfunctionsofGolgicomplexA.ThepolarityofGolgicomplex當前第14頁\共有62頁\編于星期五\17點a)CiscisternaeofGolgicomplex:reducedosmiumtetroxide(OsO4);b)ReactionforenzymemannosidaseII,localizedinthemedial;c)Reactionforenzymenucleosidediphosphatase,localizedinthetranscisternae.RegionaldifferencesinmembranecompositionacrosstheGolgistack當前第15頁\共有62頁\編于星期五\17點B.TheFunctionsofGolgicomplexGlycosylationintheGolgicomplexGolgicomplexplaysakeyroleintheassemblyofthecarbohydratecomponentofglycoproteinsandglycolipids.當前第16頁\共有62頁\編于星期五\17點ThecorecarbohydrateofN-linkedoligosaccharidesisassembledintherER.ModificationstoN-linkedoligosaccharidesarecompletedintheGolgicomplex.O-linkedoligosaccharidestakesplaceinGolgicomplex.當前第17頁\共有62頁\編于星期五\17點StructureoftypicalO-andN-linkedoligosaccharidesCoreRegionAfterR.KornfeldandS.Kornfeld,1985,Annu.Rev.Biochem.

45:631當前第18頁\共有62頁\編于星期五\17點Whatisthepurposeofglycosylation?N-linkedglycosylationisprevalentinalleucaryotes,butisabsentfromprocaryotes.Itdon’trequireatemplate.ThereisanimportantdifferencebetweentheconstructionofanoligosaccharideandthesynthesisofDNA,RNA,andprotein.Importantfunctions:

(1)Onemightsuspectthattheyfunctiontoaidfoldingandthetransportprocess;forexample,carbohydrateasamarkerduringproteinfoldinginERandtheuseofcarbohydrate-bindinglectinsinguidingER-to-Golgitransport.(2)Limittheapproachofothermacromoleculestotheproteinsurface,moreresistanttodigestionbyproteases.(3)Regulatoryrolesinsignalingthroughthecell-surfacereceptorNotch,toallowsthesecellstorespondselectivelytoactivatingstimuli.當前第19頁\共有62頁\編于星期五\17點TheGolginetworksareprocessingandsortingstationswhereproteinsaremodified,segregatedandthenshippedindifferentdirections.當前第20頁\共有62頁\編于星期五\17點

VesivulartransportwithintheGolgiapparatus:

Twoviews:cisternalmaturationmodelandvesiculartransportmodelTwopossiblemodelsexplainingtheorganizationoftheGolgicomplexandthetransportfromonecisternatothenext.當前第21頁\共有62頁\編于星期五\17點十

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.當前第22頁\共有62頁\編于星期五\17點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.當前第23頁\共有62頁\編于星期五\17點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.當前第24頁\共有62頁\編于星期五\17點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.當前第25頁\共有62頁\編于星期五\17點4.ThestructureandfunctionsofLysosomesA.CharacteristicsofLysosomes①Lysosomeisaheterogenousorganelle:PrimarylysosomesSecondlysosomesheterophagicautophagicResidualbodyPrimaryLys.SecondLys當前第26頁\共有62頁\編于星期五\17點

Figure

6-19

Histochemicalvisualizationoflysosomes.

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

當前第27頁\共有62頁\編于星期五\17點②Lysosomescontainplentyacidhydrolasesthatcandigesteverykindofbiologicalmolecule.---theprincipalsitesofintracellulardigestion.Markerenzyme:acidphosphatase③Lysosomemembrane:H+-pumps:internalprotonconcentrationiskepthighbyH+-ATPaseGlycosylatedproteins:mayprotectthelysosomefromself-digestion.

Transportproteins:transportingdigestedmaterials.當前第28頁\共有62頁\編于星期五\17點Figure

13-18

ThelowpHinlysosomesandendosomes.

ProteinslabeledwithapH-sensitivefluorescentprobe(fluorescein)andthenendocytosedbycellscanbeusedtomeasurethepHinendosomesandlysosomes.ThedifferentcolorsreflectthepHthatthefluorescentprobeencountersintheseorganelles.ThepHinlysosomes(red)isabout5,whilethepHinvarioustypesofendosomes(blueandgreen)rangesfrom5.5to6.5.(CourtesyofFredMaxfieldandKennethDunn.)當前第29頁\共有62頁\編于星期五\17點Figure

13-20

Theplantcellvacuole.

Thiselectronmicrographofcellsinayoungtobaccoleafshowsthatthecytosolisconfinedbytheenormousvacuoletoathinlayer,containingchloroplasts,pressedagainstthecellwall.Themembraneofthevacuoleiscalledthetonoplast.(CourtesyofJ.Burgess.)當前第30頁\共有62頁\編于星期五\17點B.TheFunctionsofLysosomesLysosomesareinvolvedinthreemajorcellfunctions:①phagocytosis;②autophagy;③endocytosis.Primarylysfusewitheitherphagocyticorautophagicvesicles,formingresidualbodiesthateitherundergoexocytosisorareretainedinthecellaslipofuscingranules.當前第31頁\共有62頁\編于星期五\17點C.LysosomesandDiseasesDisordersresultingfromdefectsinlysosomalfunction:①Autolysis:Abreakorleakinthemembraneoflysreleasesdigestiveenzymesintothecellwhichdamagesthesurroundingtissues(Silicosis).②

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

Tay-Sachsdiseaseresultsfromadeficiencyoftheenzyme(-N-hexosaminidaseA)whosefunctionistodegradegangliosides,amajorcomponentofbraincellmembranes.當前第32頁\共有62頁\編于星期五\17點表1.神經鞘脂貯積病疾病缺失酶類主要貯積底物后果GM1神經節(jié)苷脂貯積癥GM1-半乳糖苷酶神經節(jié)苷脂GM1智力遲鈍，肝臟肥大，骨骼受累，2歲前死亡泰－薩二氏病己糖胺酶A神經節(jié)苷脂GM2智力遲鈍，失明，3歲前死亡法布萊氏病-半乳糖苷酶A三己糖神經酰胺皮疹，腎功能喪失，下肢疼痛山霍夫氏病己糖胺酶A和B神經節(jié)苷脂GM2和紅細胞糖苷酯與泰－薩氏疾病癥狀相似，但發(fā)展更快高歇氏病葡糖腦苷酯酶葡糖腦苷脂肝臟和脾臟腫大，長骨腐蝕，只在嬰兒期發(fā)生智力遲鈍尼-皮二氏病鞘磷脂水解酶鞘磷脂肝臟和脾臟腫大，智力遲鈍Farber’s脂肪肉芽腫病神經酰胺水解酶神經酰胺疼痛性與退行性的關節(jié)變形，皮膚瘤，幾年內死亡Krabbe’s病半乳糖腦苷酯酶半乳糖腦苷脂髓磷脂缺失，智力遲鈍，2歲前死亡腦硫脂沉積芳基硫酸酯酶腦硫脂智力遲鈍，前十年死亡當前第33頁\共有62頁\編于星期五\17點D.BiogenesisofLysosomesFigure

6-23

Thetransportofnewlysynthesizedlysosomalhydrolasestolysosomes.

Theprecursorsoflysosomalhydrolasesarecovalentlymodifiedbytheadditionofmannose6-phosphateintheCGN.TheythenbecomesegregatedfromallothertypesofproteinsintheTGNbecauseaspecificclassoftransportvesiclesbuddingfromtheTGNconcentratesmannose6-phosphate-specificreceptors,whichbindthemodifiedlysosomalhydrolases.Thesevesiclessubsequentlyfusewithlateendosomes.AtthelowpHofthelateendosomethehydrolasesdissociatefromthereceptors,whicharerecycledtotheGolgiapparatusforfurtherroundsoftransport.Inlateendosomesthephosphateisremovedfromthemannoseonthehydrolases,furtherensuringthatthehydrolasesdonotreturntotheGolgiapparatuswiththereceptor.當前第34頁\共有62頁\編于星期五\17點Mannose6-phosphateresiduestargetproteinstolysosomesTargetingofsolublelysosomalenzymestoendosomesandlysosomesbyM-6-Ptag當前第35頁\共有62頁\編于星期五\17點

PhosphorylationofmannoseresiduesonlysosomalenzymescatalyzedbytwoenzymesRecognitionsitebindstoSignalpatchGlcNAcphosphotransferasephosphodiesterase當前第36頁\共有62頁\編于星期五\17點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]當前第37頁\共有62頁\編于星期五\17點5.ProteinSorting

Overviewofsortingofnuclear-encodedproteinsineukaryoticcellsProteinsareimportedintoorganellesbythreemechanisms:GatedTransport:TransportthroughnuclearporesTransmembranetransport:ER,Mit,Chl,PerVesiculartransport:ER-Golgi-PM-Lys,Endosome當前第38頁\共有62頁\編于星期五\17點

Roadmapofproteinsorting

當前第39頁\共有62頁\編于星期五\17點Proteinsorting:Proteinmoleculesmovefromthecytosoltotheirtargetorganellesorcellsurfacedirectedbythesortingsignalsintheproteins.當前第40頁\共有62頁\編于星期五\17點SignalpeptidesandSignalpatchesFigure

6-8

Twowaysthatasortingsignalcanbebuiltintoaprotein.

(A)Thesignalresidesinasinglediscretestretchofaminoacidsequence,calledasignalpeptide,thatisexposedinthefoldedprotein.Signalpeptidesoftenoccurattheendofthepolypeptidechain,buttheycanalsobelocatedelsewhere.(B)Asignalpatchcanbeformedbythejuxtapositionofaminoacidsfromregionsthatarephysicallyseparatedbeforetheproteinfolds;alternatively,separatepatchesonthesurfaceofthefoldedproteinthatarespacedafixeddistanceapartcouldformthesignal.當前第41頁\共有62頁\編于星期五\17點Gatedtransport:

Throughgatedpores—Nuclearpores;Nuclearlocalizationsignal(NLS);Foldedandassemblyformtotransport.TransmembranetransportERsignalsequence,Mit,Chl,Per:Leadersequence;Throughtranslocononthemembrane;SingleandUnfoldform;Helpedbymolecularchaperons當前第42頁\共有62頁\編于星期五\17點VesiculartransportBudding,transporting,dockingandatlastfusionwithtargetmembrane;Assemblycoatedproteinsonthevesicles(Clathrin,COPIIandCOPI);OnlyProperlyfoldedandassembledproteins;Theorientationoftransportedproteinsandlipidsisnotchangedduringtransporting.當前第43頁\共有62頁\編于星期五\17點B.SignalHypothesis

--G.Blobel&D.Sabatini,1971.AmodelfortheSignalMechanismofCotranslationalImportEvidenceThatProteinSynthesizedonRibosomesAttachedtoERMembranesPassDirectlyintotheERLumen(D.Sabatini)Milstein:IgG當前第44頁\共有62頁\編于星期五\17點Milsteinetal:StudyingthesynthesisoflightchainofIgG(incell-freesystems,20AalongeratN-terminalendthantheauthenticlightchain)AddingERmembranestothissystemleadstotheproductionofanIgGlightchainofthecorrectsize.當前第45頁\共有62頁\編于星期五\17點

ASchematicmodelforthesynthesisofasecretoryproteinonamembrane-boundribosomeoftheroughER當前第46頁\共有62頁\編于星期五\17點Signal-recognitionparticle,SRP:Sixdifferentpolypeptidescomplexedwitha300-nucleotide(7S)moleculeofRNA.ERsignalsequence:Typically15-30aminoacids:Consistofthreedomains:apositivelychargedN-terminalregion,acentralhydrophobicregion,andapolarregionadjoiningthesitewherecleavagefromthematureproteinwilltakeplace.AsignalsequenceonnascentseretoryproteinstargetsthemtotheERandisthencleavedoffSRPreceptor(GTPbindingprotein)SRPhavethreemainactivesites:OnethatrecognizesandbindstoERsignalsequence;Onethatinteractswiththeribosometoblockfurthertranslation;OnethatbindstotheERmembrane(dockingprotein))當前第47頁\共有62頁\編于星期五\17點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]當前第48頁\共有62頁\編于星期五\17點Start-transferSequence&Stop-transferSequence當前第49頁\共有62頁\編于星期五\17點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.]

當前第50頁\共有62頁\編于星期五\17點TheOrientationofNascentPolypeptide

TheNascentpolypeptideisorientedwithintransloconsothatthepositivelychargedflankingsequencefacesthecytosol當前第51頁\共有62頁\編于星期五\17點C.

AModelforthePostranslationalImportofPolypeptidesintotheMit.Post-translationalmodificationandqualitycontrolintherERDisulfidebondsareformedandrearrangedintheERlumenOnlyinERlumenistherearedoxenvironmentforoxidationof–SHgroups.PDI:proteindisulfideisomerase,foundinabundanceintheERlumen當前第52頁\共有62頁\編于星期五\17點6.

TypesofVesicleTransportandTheirFunctionsA.Thethreedifferenttypesofcoatedvesicles.Differentcoatproteinsselectdifferentcargoandshapethetransportvesiclesthatmediatethevariousstepsinthebiosynthetic-secretoryandendocyticpathways.當前第53頁\共有62頁\編于星期五\17點COPII-coatedvesiclesmovematerialsfromtheERtotheGolgi.TheassemblyofaCOPII-coatedvesicles.Sar—GTPbindingprotein:Sar-GTPbindstotheER;Sar-GDPdissociatesfromtheERAntibodiesisabletoblockthebuddingofvesiclefromERbuthavenoeffectonvesicletransportfromoneGolgicompartmenttoanotherinmammaliancell.當前第54頁\共有62頁\編于星期五\17點COPI-coatedvasiclestransportingEscapedERresidentProteinsBacktotheER.TheassemblyofaCOPI-coatismediatedbyADP-ribosylationfactor(ARF),GTPbindingprotein,whichisrequiredforvesicletransferbetweencisternae.COPIcoatedvesiclesmayselectspecificcargo.

ERisanopenprison.SolubleERproteinbearRetrievingsignal—KDEL(Lys-Asp-Glu-Leu)inmammalandHDELinyeast,whereasERmembraneproteinsbearthesignalKKXX.TheKDELreceptorpresentinvesiculartubularclustersandtheGolgiapparatus..(3)COPI-coatedvesiclewerefirstidentifiedbytreatmentofGTPanalogues---COPI-coatedvesicleaccumulatedwithinthecellandcouldbeisolatedbycentrifugation.當前第55頁\共有62頁\編于星期五\17點Clathrin-coatedvesicle:TransportingCargofromtheTGNtoendosomes,Lysosomes,andplantvacuolesandalsomovematerialsfromthePMtocytoplasmiccompartmentsalongtheendocyticpathway.TheTGNofGolgiistheSourseofClathrin-coatedvesicle.(2)Clathrin-coatscontain:

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

當前第56頁\共有62頁\編于星期五\17點B.TheSNAREHypothesisforTransportVesicleTargetingandFusionSpecificityinvesicledockingandfusionisthoughttobeattainedthroughspecificinteractionsbetweenspecificv-SNAREproteinsonthevesiclemembranesandt-SNAREproteinsonthemembranesofthetargetcompartment.SNAREsareaproteinfamily.Thereareatleast20differentSNAREsinananimalcell.TheroleofSNAREsinguidingvesiculartransport.當前第57頁\共有62頁\編于星期五\17點我勸一個草率結婚的朋友離婚。她平靜的告訴我，如果說當初魯莽結婚是個錯誤。那么，現(xiàn)在草率離婚是一錯再錯。這位朋友后來還是離婚了，大家一致認為她的行為很理性。

同樣的故事正在互聯(lián)網(wǎng)搜索巨頭谷歌身上發(fā)生，但是谷歌選擇了草率“離婚”。

飲鴆止渴

由于急于抑制蘋果iphone手機翻天覆地的產業(yè)沖擊，谷歌采取急功近利的粗糙型開放策略。飲鴆止渴的策略一時取得了成果。市場研究公司尼爾森最近公布的數(shù)據(jù)顯示，在通過VerizonWireless、AT&T和SprintNextel三大運營商經銷后，谷歌Android手機在美國市場上的銷售量已經超過iPhone。另一家市場研究公司iSuppli甚至認為，全球范圍內使用Android操作系統(tǒng)的手機數(shù)量將在2012年超過蘋果iPhone。

表面繁華的背后，是Android生態(tài)系統(tǒng)的一團糟，谷歌正在為自己的粗放型開放策略買單。

用戶對谷歌手機的態(tài)度從開始的好奇、后來的猶豫，變成強烈的批評。“大多Android手機程序都是垃圾，亂七八糟的”，一位手機發(fā)燒友迅速投奔了iphone的陣營：“同樣的植物人大戰(zhàn)僵尸游戲，在谷歌手機和iphone手機上的體驗簡直沒法比”

混亂，還是混亂。一切一切的亂象，折射出谷歌已經失去對Android生態(tài)系統(tǒng)的控制。這一切的根源，我的判斷是開放策略初期過于寬松，導致失去控制權?；靵y的生態(tài)系統(tǒng)表現(xiàn)在用戶手機上，就是應用程序的混亂和粗燥。

一錯再錯

為此，谷歌開始采取對策。最近，有國內廠商稱新的Android3.0開始關閉應用程序的API(應用程序編程接口)，統(tǒng)一Android界面。這意味著，谷歌將放棄其初始開放策略，開始封閉管理。

粗看之下，谷歌認識到自己的錯誤。既然是過度開放導致的錯誤，那么收緊開放尺度是很自然的邏輯，無懈可擊。但我認為，谷歌倉促收緊開放策略仍然是個錯誤。打個比喻。如果過度開放的政策是草率結婚，那么草率的封閉就是草率離婚。這么判斷的原因很簡單，谷歌把Android開放出去的那一天，Android已經不屬于谷歌。谷歌沒有認識到這一點，還以為Android只是自己的。

合作伙伴對谷歌封閉政策的反應加強了我的判斷結論。經濟觀察報報道，國內第一家生產基于Android平臺手機的設計公司創(chuàng)楊通信，近日已經被迫出售。創(chuàng)楊通信負責人給出的出售理由是，“因為不愿意甘當炮灰而選擇放棄?！?/p>

按照目前Android3.0將統(tǒng)一界面的想法，未來的手機市場將出現(xiàn)毫無差異化的產品。這對于企業(yè)來說，幾乎意味著不可避免的價格戰(zhàn)。利潤空間的微薄，導致合作伙伴生存環(huán)境惡劣。于是大量退出幾乎是一種必然。

除了為合作伙伴找到新的利益空間，谷歌還將面臨開放陣營精神層面的聲討，這對谷歌的挑戰(zhàn)會更大。如果說谷歌為了自己競爭的私利利用了開放，贏得了名聲。那么，谷歌不能一腳把開放踢開，他現(xiàn)在還需要為這種名聲買單。

如果只顧自己收網(wǎng)，谷歌會被面臨鋪天蓋地的道德譴責。谷歌，希望你準備好了，三思而行。

木桶效應就是指一個水桶無論有多高，它盛水的高度取決于其中最低的那塊木板。這在選購手機的時候也同樣適用。尤其是很多用戶在購買手機的時候，都會專注于某一個參數(shù)，比如要求處理器主頻要高達1GHz，但一部手機的整機表現(xiàn)是由多個因素組成，所以在購買手機的時候一定要從整體的角度上來看一部手機的性除了處理器主頻以外，其實還有很多影響整機表現(xiàn)的元素，比如運行內存(RAM)、機身內存(ROM)、操作系統(tǒng)、廠商對系統(tǒng)的優(yōu)化都會有所影響。不過在很多用戶眼中，這幾項卻遠沒有處理器主頻重要。而如果忽略這幾項的話，可能買到一個主頻很高，但整機性能卻仍然不令人滿意的機型。

用戶在選機過程中切勿只關注一個硬件參數(shù)，這樣很可能并不能買到一款理想的機型，就算買的手機主頻再高，運行內存低的話仍然無法同時運行數(shù)個程序、機身內存小的話則無法把太多的軟件安裝到機器上，這對整機耗電和運行速度方面都有所影響、而廠商優(yōu)化更是決定著一部手機的穩(wěn)定性和部分運行速度。綜上所述，大家在選購手機的時候一定要綜合考慮一款手機的硬件規(guī)格。除此之外，也不要把硬件看的太過重要，就比如蘋果iPhone3GS在硬件配置上并不出眾，但卻在操控手感以及軟件資源上目前難有機型企及。更高分辨率能獲得更為逼真細膩的顯示效果，所以對于屏幕的分辨率絕大多數(shù)人都會偏向于分辨率更高的機型。但對于筆者所說的高分辨率未必是好事會有所懷疑。其實這里說的高分辨率“不好”更多是指采用非主流的高分辨率機型。在此前，就有幾款“悲情”機型在分辨率上吃了不小的虧。

大名鼎鼎的HTCDiamond就是一款頗具代表意義的機型，Diamond上市的手機市場還處于QVGA時代、只有少數(shù)旗艦機皇采用WVGA這樣級別的屏幕，由于HTCDiamond卻采用了VGA這一過渡型的分辨率，而也正是因為這一點，Diamond很多軟件都未有支持或無法完美運行，可謂是一個不小的遺憾。除此之外，曾經非常經典的

當前第58頁\共有62頁\編于星期五\17點附贈人生心語人生太短，聰明太晚人生太短，聰明太晚(1)

我們都老得太快

卻聰明得太遲把錢省下來，等待退休后再去享受結果退休后，因為年紀大，身體差，行動不方便，哪里也去不成。錢存下來等養(yǎng)老，結果孩子長大了，要出國留學，要創(chuàng)業(yè)做生意，要花錢娶老婆，自己的退休金都被拗走了。人生太短，聰明太晚(2)

當自己有足夠的能力善待自己時，就立刻去做，老年人有時候是無法做中年人或是青少年人可以做的事，年紀和健康就是一大因素。小孩子從小就告訴他，養(yǎng)你到高中，大學以后就要自立更生，要留學，創(chuàng)業(yè)，娶老婆，自己想辦法，自己要留多一點錢，不要為