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1、19MICROFILAMENTSANDINTERMEDIATEFILAMENTSThemacrophagecytoskeleton.Prominentstructuresincludeanetworkofintermediatefilaments(red)andthepunctatedis-tributionsofcelladhesions(yellow)containingbothactinandvimentin.[CourtesyofJ.Evans.]heabilityofcellstomigrateis
2、oneofthecrowningdiscretestructures—primarilybundles,geodesic-dome-likeachievementsofevolution.Primitivecellsprobablynetworks,andgel-likelattices.Inthischapter,weextendourTlackedsuchself-generatedmovement(motility),de-earlierconsiderationofactinmicrofilament
3、sandintermediatependingoncurrentsintheprimordialmilieutomovethemfilaments(Figure19-1).Bothofthesecytoskeletalcompo-about.Inmulticellularorganisms,however,themigrationofnentsareusuallyattachedtoplasmamembraneproteinsandsinglecellsandgroupsofcellsfromoneparto
4、fanembryotoformaskeletonthathelpssupporttheplasmamembrane.anotheriscriticaltothedevelopmentoftheorganism.InHowever,actinfilamentsparticipateinseveraltypesofcelladultanimals,singlecellssearchoutforeigninvadersaspartmovements,whereasintermediatefilamentsareno
5、tdirectlyofahost’sdefensesagainstinfection;ontheotherhand,un-engagedincellmovements.controlledcellmigrationisanominoussignofacancerousAllcellmovementsareamanifestationofmechanicalcell.Somebacterialcellscanmovebythebeatingofflagellawork;theyrequireafuel(ATP)
6、andproteinsthatconvertthepoweredbyarotarymotorinthecellmembrane(seeFigureenergystoredinATPintomotion.Cellshaveevolvedtwo3-22b).Motileeukaryoticcells,however,usedifferentmech-basicmechanismsforgeneratingmovement.Onemechanismanismstogeneratemovement.entailsth
7、eassemblyanddisassemblyofmicrofilamentsandEvenstationarycells,whichpredominateinthebody,microtubules;itisresponsibleformanychangesincellmayexhibitdramaticchangesintheirmorphology—thecon-shape.Theothermechanismrequiresaspecialclassofen-tractionofmusclecells,
8、theelongationofnerveaxons,thezymescalledmotorproteins,firstdescribedinChapter3.formationofcell-surfaceprotrusions,theconstrictionofaTheseproteinsuseenergyfromATPtowalkorslidealongdividingcellinmitosis.
