普通生物學(xué)課件

Biology普通生物學(xué)

Biology(7thedition)Campbell,Reece授課老師:賴金美(LS303)bio2028@.twBiology普通生物學(xué)Overview:TheImportanceofCellsAllorganismsaremadeofcells.Thecellisthesimplestcollectionofmatter

thatcanlive.10μmOverview:TheImportanceofCeConcept6.1:Tostudycells,biologistsusemicroscopesandthetoolsofbiochemistryLightmicroscopes(LMs)PassvisiblelightthroughaspecimenMagnifycellularstructureswithlensesScientistsusemicroscopestovisualizecellstoosmalltoseewiththenakedeyeConcept6.1:Tostudycells,bLightmicroscope(LM)

Twoimportantparameters:

---magnification

1000X

~theratioofanobjectsimagetoitsrealsize---resolvingpower(orresolution)

~ameasureoftheclarityoftheimageLimit:

~0.2mm(200nm)

Resolution:badgoodLightmicroscope(LM)ResolutiDifferenttypesofmicroscopesCanbeusedtovisualizedifferentsizedcellularstructuresUnaidedeye1m0.1nm10m0.1m1cm1mm100μm10μm1μm100nm10nm1nmLengthofsomenerveandmusclecellsChickeneggFrogeggMostplant

andAnimalcellsSmallestbacteriaVirusesRibosomesProteinsLipidsSmallmoleculesAtomsNucleus

Mostbacteria

MitochondrionLightmicroscopeElectronmicroscopeElectronmicroscopeFigure6.2HumanheightMeasurements1centimeter(cm)=102meter(m)=0.4inch1millimeter(mm)=10–3m1micrometer(μm)=10–3mm=10–6m1nanometer(nm)=10–3mm=10–9mDifferenttypesofmicroscopesUsedifferentmethodsforenhancingvisualizationofcellularstructuresTECHNIQUERESULTBrightfield(unstainedspecimen).Passeslightdirectlythroughspecimen.Unlesscellisnaturallypigmentedorartificiallystained,imagehaslittlecontrast.[Parts(a)–(d)showahumancheekepithelialcell.](a)Brightfield(stainedspecimen).

Stainingwithvariousdyesenhances

contrast,butmoststainingprocedures

requirethatcellsbefixed(preserved).(b)Phase-contrast.Enhancescontrastinunstainedcellsbyamplifyingvariationsindensitywithinspecimen;especiallyusefulforexaminingliving,unpigmentedcells.(c)50μmFigure6.3UsedifferentmethodsforenhaDifferential-interference-contrast(Nomarski).

Likephase-contrastmicroscopy,itusesopticalmodificationstoexaggeratedifferencesindensity,makingtheimageappearalmost3D.Fluorescence.Showsthelocationsofspecificmoleculesinthecellbytaggingthemoleculeswithfluorescentdyesorantibodies.Thesefluorescentsubstancesabsorbultravioletradiationandemitvisiblelight,asshownhereinacellfromanartery.Confocal.Useslasersandspecialopticsfor“opticalsectioning”offluorescently-stainedspecimens.Onlyasingleplaneoffocusisilluminated;out-of-focusfluorescenceaboveandbelowtheplaneissubtractedbyacomputer.Asharpimageresults,asseeninstainednervoustissue(top),wherenervecellsaregreen,supportcellsarered,andregionsofoverlapareyellow.Astandardfluorescencemicrograph(bottom)ofthisrelativelythicktissueisblurry.50μm(d)(e)(f)Differential-interference-contElectronmicroscope(EM)

---Focusabeamofelectronsthroughaspecimen(TEM)orontoitssurface(SEM)

Limit:

~2nm(0.002nmtheoretically)

(ahundredfoldimprovementoverthelightmicroscope)“Cellultrastructure“However,mostsubcellularstructures,ororganelles,aretoosmalltoberesolvedbytheLM.Until1950s,withtheintroductionoftheelectronmicroscopeElectronmicroscope(EM)“CelThescanningelectronmicroscope(SEM)Providesfordetailedstudyofthesurfaceofaspecimen.TECHNIQUERESULTSScanningelectronmicro-scopy(SEM).Micrographstakenwithascanningelectronmicro-scopeshowa3Dimageofthesurfaceofaspecimen.ThisSEMshowsthesurfaceofacellfromarabbittrachea(windpipe)coveredwithmotileorganellescalledcilia.Beatingoftheciliahelpsmoveinhaleddebrisupwardtowardthethroat.(a)Cilia1μmFigure6.4(a)ThescanningelectronmicroscoThetransmissionelectronmicroscope(TEM)ProvidesfordetailedstudyoftheinternalultrastructureofcellsTransmissionelectronmicro-scopy(TEM).Atransmissionelectronmicroscopeprofilesathinsectionofaspecimen.Hereweseeasectionthroughatrachealcell,revealingitsultrastructure.InpreparingtheTEM,someciliawerecutalongtheirlengths,creatinglongitudinalsections,whileotherciliawerecutstraightacross,creatingcrosssections.(b)LongitudinalsectionofciliumCrosssectionofcilium1μmFigure6.4(b)ThetransmissionelectronmicrCellfractionationTakescellsapartandseparatesthemajororganellesfromoneanotherIsolatingOrganellesbyCellFractionationThecentrifugeIsusedtofractionatecellsintotheircomponentparts(separatethecellcomponentsbysizeanddensity)Why?

tostudythefunctionoftheorganellesCellfractionationIsolatingOrCellfractionationisusedtoisolate(fractionate)cellcomponents,basedonsizeanddensity.First,cellsarehomogenizedinablendertobreakthemup.Theresultingmixture(cellhomogenate)isthencentrifugedatvariousspeedsanddurationstofractionatethecellcomponents,formingaseriesofpellets.TheprocessofcellfractionationAPPLICATIONTECHNIQUEFigure6.5CTissuecellsHomogenizationHomogenate1000g(1000timestheforceofgravity)10minDifferentialcentrifugationSupernatantpouredintonexttube20,000g20minPelletrichinnucleiandcellulardebrisPelletrichinmitochondria(andchloro-plastsifcellsarefromaplant)Pelletrichin“microsomes”(piecesofplasmamem-branesandcells’internalmembranes)Pelletrichinribosomes150,000g3hr80,000g60minFigure6.5usedmicroscopytoidentifytheorganellesineachpelletusedbiochemicalmethodstodeterminethemetabolicfunctionsassociatedwitheachtypeoforganelle.TissueHomogenizationHomogenateCellbiologistscanisolateorganellestostudytheirfunctionsCytologyBiochemistryrpm(revolutionsperminute)(b)xg(forceofgravity)Cytologyandbiochemistrycomplementeachotherincorrelatingcellularstructureandfunction.CellbiologistscanisolateorConcept6.2:EukaryoticcellshaveinternalmembranesthatcompartmentalizetheirfunctionsTwotypesofcellsmakeupeveryorganismProkaryoticEukaryoticAllcellshaveseveralbasicfeaturesincommonTheyareboundedbyaplasmamembraneTheycontainasemifluidsubstancecalledthecytosolTheycontainchromosomesTheyallhaveribosomesConcept6.2:EukaryoticcellsProkaryoticcellsDonotcontainanucleusHavetheirDNAlocatedinaregioncalledthenucleoid(b)AthinsectionthroughthebacteriumBacilluscoagulans(TEM)Pili:attachmentstructuresonthesurfaceofsomeprokaryotesNucleoid:regionwherethecell’sDNAislocated(notenclosedbyamembrane)Ribosomes:organellesthatsynthesizeproteinsPlasmamembrane:membraneenclosingthecytoplasmCellwall:rigidstructureoutsidetheplasmamembraneCapsule:jelly-likeoutercoatingofmanyprokaryotesFlagella:locomotionorganellesofsomebacteria(a)Atypicalrod-shapedbacterium0.5μmBacterial

chromosomeProkaryoticcells(b)AthinseEukaryoticcellsContainatruenucleus,boundedbyamembranousnuclearenvelope.AregenerallyquiteabitbiggerthanprokaryoticcellsRoughERSmoothERCentrosomeCYTOSKELETONMicrovilliLysosomeGolgiapparatusRibosomesNucleolusChromatinNUCLEUSFlageliumENDOPLASMICRETICULUM(ER)MitochondrionNuclearenvelopePlasmamembranecytoplasm-Containingavarietyofmembrane-boundedorganelles.EukaryoticcellsRoughERSmoothProkaryoticvsEukaryoticcells(原核)(真核)DifferinsizeandcomplexityBasicfeatures:plasmamembrane,cytosol,chromosomes,ribosomes,…Difference:asindicatedbytheirnames:ProkaryoticEukaryotic

nucleoidnucleus(nomembrane)

(containingmembranousnuclearenvelope)Chromosomeslocationonlyribosome(organelles)1-10mm10-100mmcytoplasmsizeProkaryoticvsEukaryoticSurfaceareaincreaseswhiletotalvolumeremainsconstant511Totalsurfacearea(heightwidth

numberofsides

numberofboxes)Totalvolume(heightwidthlengthnumberofboxes)Surface-to-volumeratio(surfaceareavolume)6161501251.27501256ThelogisticsofcarryingoutcellularmetabolismsetslimitsonthesizeofcellsAsmallercellHasahighersurfacetovolumeratio,whichfacilitatestheexchangeofmaterialsintoandoutofthecellSurfaceareaincreaseswhile51TheplasmamembraneFunctionsasaselectivebarrierAllowssufficientpassageofnutrients

andwasteFigure6.8A,BCarbohydratesidechainOutsideofcellInsideofcellHydrophilicregionHydrophobicregionHydrophilicregion(b)StructureoftheplasmamembranePhospholipidProteinsTEMofaplasmamembrane.Theplasmamembrane,hereinaredbloodcell,appearsasapairofdarkbandsseparatedbyalightband.(a)0.1μmTheplasmamembraneFigure6.8EukaryoticcellsHaveextensiveandelaboratelyarrangedinternalmembranes,whichformorganellesAPanoramicViewoftheEukaryoticCellRoughERSmoothERCentrosomeCYTOSKELETONMicrofilamentsMicrotubulesMicrovilliPeroxisomeLysosomeGolgiapparatusRibosomesInanimalcellsbutnotplantcells:LysosomesCentriolesFlagella(insomeplantsperm)NucleolusChromatinNUCLEUSFlageliumIntermediatefilamentsENDOPLASMICRETICULUM(ER)MitochondrionNuclearenvelopePlasmamembraneEukaryoticcellsAPanoramicViAplantcellInplantcellsbutnotanimalcells:ChloroplastsCentralvacuoleandtonoplastCellwallPlasmodesmataCYTOSKELETONRibosomes(smallbrwondots)CentralvacuoleMicrofilamentsIntermediatefilamentsMicrotubulesRoughendoplasmicreticulumSmoothendoplasmicreticulumChromatinNUCLEUSNuclearenvelopeNucleolusChloroplastPlasmodesmataWallofadjacentcellCellwallGolgiapparatusPeroxisomeTonoplastCentrosomePlasmamembraneMitochondrionFigure6.9AplantcellInplantcellsbutConcept6.3:Theeukaryoticcell’sgeneticinstructionsarehousedinthenucleusandcarriedoutbytheribosomes.ThenucleusContainsmostofthegenesintheeukaryoticcell

(somegenesarelocatedinmitochondriaandchloroplasts)ThenuclearenvelopeEnclosesthenucleus,separatingitscontentsfromthecytoplasmNucleusNucleolusChromatinNuclearenvelope:InnermembraneOutermembraneNuclearporeRoughERPorecomplexConcept6.3:TheeukaryoticceNucleusNucleusNucleolusChromatinNuclearenvelope:InnermembraneOutermembraneNuclearporeRoughERPorecomplexSurfaceofnuclear

envelope.Porecomplexes(TEM).Nuclearlamina(TEM).

Close-upof

nuclearenvelopeRibosome1μm1μm0.25μmThenuclearenvelopeIsadoublemembrane(separatedbyaspaceof20-40nm)Nuclearpore

(100nmindiameter)NuclearlaminaNuclearmatrixChromatin

(acomplexofproteinsandDNA)nucleolus

(rRNA&protein)NucleusNucleusNucleolusChromatRibosomesAreparticlesmadeofribosomalRNAandproteinCarryoutproteinsynthesis---freeribosomes:incytosol

boundribosomes:attachedtooutsideoftheERornuclearenvelopRibosomes:ProteinFactoriesintheCellERRibosomesCytosolFreeribosomesBoundribosomesLargesubunitSmallsubunitTEMshowingERandribosomesDiagramofaribosome0.5μmEndoplasmicreticulum(ER)StructurallyidenticalandcanalternatebetweenthetworolesRibosomesRibosomes:ProteinFa~includingthenuclearenvelope,endoplasmicreticulum(ER),Golgiapparatus,lysosomes,vacuoles,andtheplasmamembrane.(relatedeitherthroughdirectphysicalcontinuity

orbythetransferofmembranesegmentastinyvesicles.)Concept6.4:Theendomembranesystemregulatesproteintrafficandperformsmetabolicfunctionsinthecell

TheendomembranesystemIncludesmanydifferentstructures~includingthenuclearenveloTheendoplasmicreticulum(ER)AccountsformorethanhalfthetotalmembraneinmanyeukaryoticcellsEndoplasmicreticulum(ER)

endoplasmic-“withinthecytoplasm”reticulum-“l(fā)ittlenet”

*cisternae(membranoustubulesandsacs;reservoirforaliquid)

cytosol---ERlumen(cisternalspace)*smoothER:lacksribosomesroughER:containingribosomes(cytoplasmicsurface)Theendoplasmicreticulum(ER)TheERmembraneIscontinuouswiththenuclearenvelopeSmoothERRoughERERlumenCisternaeRibosomesTransportvesicleSmoothERTransitionalERRoughER200μmNuclearenvelopeFigure6.12TherearetwodistinctregionsofERSmoothER,whichlacksribosomesRoughER,whichcontainsribosomesTheERmembraneSmoothERRoughSmoothER:

functionsindiversemetabolicprocessesinvariouscelltypes,includingsynthesisoflipids,metabolismofcarbohydrates,

storeCa2+

anddetoxification

ofdrugsandpoisons.

*steroids:sexhormones(testesandovariesarerichinsmoothER)*Livercells

(detoxificationex.sedativephenobarbitalhowever,increasetoleurance)*Musclecell:sERstoreCa2+

Ca2+pump(cytosolERlumen)SmoothER:(detoxificationex.TransportvesiclesSmoothERRoughERERlumenCisternaeRibosomesTransportvesicleTransitionalERNuclearenvelopeRoughER:

*synthesizesecretoryproteins.ex.Pancreas:insulin~mostsecretoryproteinsareglycoproteins(thecarbohydrateisattachedtotheproteinintheER)

*membranefactory:

membraneproductionTransportvesiclesSmoothERRouTheGolgiapparatusReceivesmanyofthetransportvesiclesproducedintheroughERAsacenterofmanufacturing,warehousing,sorting,andshippingConsistsofflattenedmembranoussacscalledcisternaeTheGolgiApparatus:ShippingandReceivingCenterFunctionsoftheGolgiapparatusincludeModificationoftheproductsoftheroughERManufactureofcertainmacromolecules(ex.pectinandnon-cellulosepolysaccharides)TheGolgiapparatusTheGolgiAGolgiapparatusTEMofGolgiapparatuscisface(“receiving”sideofGolgiapparatus)VesiclesmovefromERtoGolgiVesiclesalsotransportcertainproteinsbacktoERVesiclescoalescetoformnewcisGolgicisternaeCisternalmaturation:Golgicisternaemoveinacis-to-transdirectionVesiclesformandleaveGolgi,carryingspecificproteinstootherlocationsortotheplasmamem-braneforsecretionVesiclestransportspecificproteinsbackwardtonewerGolgicisternaeCisternaetransface(“shipping”sideofGolgiapparatus)0.10μm165234Golgiapparatus:hasadistinctpolarityFigure6.13“cisternalmaturationmodel”GolgiTEMofGolgiapparatuscisAlysosome---acidic

pH(pH5)IsamembranoussacofhydrolyticenzymesCandigestallkindsofmacromoleculesHydrolyticenzymesandlysosomalmembranearemadebyrERGolgiLysosomes:DigestiveCompartmentsLysosomescarryoutintracellulardigestionbyPhagocytosis(吞噬作用)digestionproducts

passintothecytosolandbecomethe

nutrientsforthecell.

-autophagy:recyclethecell’sownorganicmaterial.ex.Liver.Alysosome---acidicpH(pH5)LysosomescarryoutintracellulardigestionbyPhagocytosisFigure6.14A(a)Phagocytosis:lysosomedigestingfood1μmLysosomecontainsactivehydrolyticenzymesFoodvacuole

fuseswith

lysosomeHydrolyticenzymesdigestfoodparticlesDigestionFoodvacuolePlasmamembraneLysosomeDigestiveenzymesLysosomeNucleusLysosomescarryoutintracelluAutophagyFigure6.14B(b)Autophagy:lysosomebreakingdowndamagedorganelleLysosomecontainingtwodamagedorganelles1μmMitochondrionfragmentPeroxisomefragmentLysosomefuseswithvesiclecontainingdamagedorganelleHydrolyticenzymesdigestorganellecomponentsVesiclecontainingdamagedmitochondrionDigestionLysosome*Tay-Sachsdisease:alipid-digestingenzymeismissingorinactiveAutophagyFigure6.14B(b)AutoAplantorfungalcellMayhaveoneorseveralvacuolesVacuoles:DiverseMaintenanceCompartmentsFoodvacuolesAreformedbyphagocytosisContractilevacuolesPumpexcesswateroutofprotistcellsAplantorfungalcellVacuolesCentralvacuolesArefoundinplantcells,enclosedbytonoplast.HoldreservesofimportantorganiccompoundsandwaterCentralvacuoleCytosolTonoplastCentralvacuoleNucleusCellwallChloroplast5μmFigure6.15largest~80%function:storage,wastedisposal,protection,andgrowth.CentralvacuolesCentralvacuolPlasmamembraneexpandsbyfusionofvesicles;proteinsaresecretedfromcellTransportvesiclecarriesproteinstoplasma

membraneforsecretionLysosomeavailableforfusionwithanothervesiclefordigestion456NuclearenvelopeisconnectedtoroughER,

whichisalsocontinuouswithsmoothERNucleusRoughERSmoothERcisGolgitransGolgiMembranesandproteinsproducedbytheERflowintheformoftransportvesiclestotheGolgiNuclearenvelopGolgipinchesofftransportVesiclesandothervesicles

thatgiverisetolysosomesandVacuoles132PlasmamembraneRelationshipsamongorganellesoftheendomembranesystemFigure6.16TheEndomembraneSystem:AReviewPlasmamembraneexpandsTConcept6.5:MitochondriaandchloroplastschangeenergyfromoneformtoanotherMitochondriaArethesitesofcellularrespirationChloroplastsFoundonlyinplants,arethesitesofphotosynthesisConcept6.5:MitochondriaandOthermembranousorganelles

Mitochondria&Chloroplasts

---mainenergytransformersofcells.---notpartoftheendomembranesystem.membraneproteinsaremadebyfreeribosomesinthecytosol

andby

ribosomescontainedwithinthemselves.

---containingribosomes,andasmallamountofDNA.---semiautonomousorganelles(growthandreproduce)

Mitochondria:cellularrespiration(generatesATPbyextractingenergyfromsugars,fats,andotherfuelswiththehelpofO2)

Chloroplasts:photosynthesis(onlyinplantsandalgae)

OthermembranousorganellesMitochondriaArefoundinnearlyalleukaryoticcellsMitochondria:ChemicalEnergyConversionMitochondriaareenclosedbytwomembranesAsmoothoutermembraneAninnermembranefoldedintocristaeMitochondrionIntermembranespaceOutermembraneFreeribosomesinthemitochondrialmatrixMitochondrialDNAInnermembraneCristaeMatrix100μmMitochondriaMitochondria:ChemThechloroplastIsaspecializedmemberofafamilyofcloselyrelatedplantorganellescalledplastids(ex.amyloplast,chromoplast)ContainschlorophyllArefoundinleavesandothergreenorgansofplantsandinalgaeChloroplasts:CaptureofLightEnergyChloroplastChloroplastDNARibosomesStromaInnerandoutermembranesThylakoid1μmGranumChloroplaststructureincludes-Thylakoids,membranoussacs-Stroma,theinternalfluidThechloroplastChloroplasts:CPeroxisomes

SinglemembraneContainenzymethattransferhydrogenfromvarioussubstratestooxygen,producinghydrogenperoxideasaby-product.ChloroplastPeroxisomeMitochondrion1μmFigure6.19Peroxisomes:Oxidation*Breakfattyaciddowntosmallermoleculesmitochondria*DetoxificationinliverAlsocontainenzymethatconvertstheH2O2towater(proteinsaremadeprimarilyinthecytosol,lipidsaremadeintheER,andwithintheperoxisomeitself)PeroxisomesChloroplastPeroxisoConcept6.6:ThecytoskeletonisanetworkoffibersthatorganizesstructuresandactivitiesinthecellThecytoskeletonIsanetworkoffibersextendingthroughoutthecytoplasmMicrotubule0.25μmMicrofilamentsFigure6.20Concept6.6:ThecytoskeletonCytoskeleton

---composedofthreewell-definedfilamentousstructures

-Microtubules(tubulin)-Microfilaments(actin)-IntermediatefilamentsCytoskeletonRolesoftheCytoskeleton:Support,Motility,andRegulationThecytoskeleton~Givesmechanicalsupporttothecell(maintainshape)~providesanchorageformanyorganellesandcytosolicenzymemolecules~Isinvolvedincellmotility

(changesincelllocationormorelimitedmovementsofpartofthecell)whichutilizesmotorproteinsRolesoftheCytoskeleton:SupVesicleATPReceptorformotorproteinMotorprotein(ATPpowered)Microtubuleofcytoskeleton(a)Motorproteinsthatattachtoreceptorsonorganellescan“walk”theorganellesalongmicrotubulesor,insomecases,microfilaments.MicrotubuleVesicles0.25μm(b)Vesiclescontainingneurotransmittersmigratetothetipsofnervecellaxonsviathemechanismin(a).InthisSEMofasquidgiantaxon,two

vesiclescanbeseenmovingalongamicrotubule.(Aseparatepartofthe

experimentprovidedtheevidencethattheywereinfactmoving.)Figure6.21A,BCytoskeletalelementsandmotorproteinsworktogetherwithplasmamembranemoleculestoallowwholecellstomovealongfiversoutsidethecell.(changeincelllocation)ThevesiclesthatbudofffromtheERtraveltotheGolgialongtracksbuiltofcytoskeletalelements.(movementsofpartofthecell)

VesicleATPReceptorforMotorprTherearethreemaintypesoffibersthatmakeupthecytoskeletonTable6.1TherearethreemaintypesofMicrotubules

---hollowtubes;25nm(13columnsoftubulinmolecules)---tubulinmolecules:adimerconsisting

a-,andb-tubulin---dynamic(200nm~25mminlength)---*compression-resisting---1.shapeandsupportthecell2.serveastracksformovingtheorganelles(withmotorprotein)ex.~guidesecretoryvesicles:(Golgiapparatusplasmamembrane)~chromosomemovementsincelldivision---constructionofcentrosomes,ciliaandflagella

MicrotubulesCentrosomesandcentrioles“microtubule-organizingcenter”(MTOC)~inmanycells,microtubulesgrowoutfromacentrosome

(nearnucleus)9tripletMT*Apairofcentrioles(notessentialfororganizingmicrotubuleassembly;mostplantslackcentrioles)Centrosomesandcentrioles“micCiliaandflagellaContainspecializedarrangementsofmicrotubulesArelocomotorappendagesthatprotrudefromsomecellsFlagellabeatingpatternDirectionofswimmingFigure6.23CiliarymotionCiliaandflagellaFlagellabeaCiliaandflagellashareacommonultrastructure(a)(c)(b)OutermicrotubuledoubletDyneinarmsCentralmicrotubuleOuterdoubletscross-linkingproteinsinsideRadialspokePlasmamembraneMicrotubulesPlasmamembraneBasalbody0.5μm0.1μm0.1μmCrosssectionofbasalbodyTripletFigure6.24A-C~eachhasacoremicrotubulessheathedinanextensionoftheplasmamembrane.“9+2”pattern

(9doublets&2centralmicrotubule)moterproteinstructurallyidenticaltoacentrioleCiliaandflagellashareacomTheproteindynein---motorprotein-Isresponsibleforthebendingmovementofciliaandflagella-“ATP”drivingtheconformationalchangeofdynein

MicrotubuledoubletsATPDyneinarmPoweredbyATP,thedyneinarmsofonemicrotubuledoubletgriptheadjacentdoublet,pushitup,release,andthengripagain.Ifthetwomicrotubuledoubletswerenotattached,theywouldsliderelativetoeachother.(a)Figure6.25ATheproteindynein---motorpOuterdoubletscross-linkingproteinsAnchorageincellATPInaciliumorflagellum,twoadjacentdoubletscannotslidefarbecausetheyarephysicallyrestrainedbyproteins,sotheybend.(OnlytwoofthenineouterdoubletsinFigure6.24bareshownhere.)(b)Figure6.25B132*radialspokesOuterdoubletsAnchorageATPInaMicrofilaments(ActinFilaments)0.25μmMicrovillusPlasmamembraneMicrofilaments(actinfilaments)IntermediatefilamentsFigure6.26“Cortex”outercytoplasmiclayer---

semisolidgel~Arebuiltfrommoleculesoftheproteinactin~beartension(pullingforces)~Incombinationwithotherproteins,theyforma3Dnetworkjustinsidetheplasmamembrane,helpingsupportthecell’sshape.~Ex.foundinmicrovilliMicrofilaments(ActinFilamentMicrofilamentsthatfunctionincellularmotilityContaintheprotein

myosin

inadditionto

actinContractionofthemusclecellresultsfromtheactinandmyosinfilamentsslidingpastonanother,shorteningthecellActinfilamentMyosinfilamentMyosinmotorsinmusclecellcontraction.(a)MusclecellMyosinarmFigure6.27AMicrofilamentsthatfunctioniAmoeboidmovement(localizedcontraction)InvolvesthecontractionofactinandmyosinfilamentsCortex(outercytoplasm):gelwithactinnetworkInnercytoplasm:solwithactinsubunitsExtendingpseudopodium(b)AmoeboidmovementFigure6.27BPseudopodiaextendandcontractthroughthereversibleassemblyofactinsubunitsintomicrofilamentsandofmicrofilamentsinnetworksthatconvertcytoplasmfromsoltogel.Amoeboidmovement(localizedcCytoplasmicstreamingNonmovingcytoplasm(gel)ChloroplastStreamingcytoplasm(sol)ParallelactinfilamentsCellwall(b)CytoplasmicstreaminginplantcellsFigure6.27C~Isanotherformoflocomotioncreatedbymicrofilaments~Bothactin-myosininteractionsandsol-geltransformation

broughtbyactinmayinvolvedin.~Commoninlargeplantcells,speedsthedistributionofmaterialswithinthecell.CytoplasmicstreamingNonmovingIntermediatefilaments

---8~12nm,specializedforbearingtension---areadiverseclassofcytoskeletalelements(belongtoafamilyofproteincontaining“keratins”)---aremorepermanentfixturesofcellsthanmicrofilamentsandmicrotubules.---Maintenanceofcellshape(reinforcingtheshapeofacell)fixorganellesinplace

FormationofnuclearlaminaIntermediatefil