天才一秒记住【畅想小说网】地址：http://www.cxtra.net
Microtubules（Mt）—dynamiccytoskeletalpos，whistantlyassembledaiditywithioplasm，andactas‘rails’foriransport.
Mitoi）—arethesiteseionforallcellularauu）—sthe‘blueprint’forallcellactivity，storediheDNA，whiecessitatestaiooplas
Nuvelope（hedoublemembraingnud.Theoutermembrainuouswiththeendoplasmicreticulu
Nuclearpores（NP）—thousandsofelsinthehattroltherapidexgesbetweennud.
Nuo）—siteoftratedRNAandribosomeprodu.
Plasmamembrane（Pm）—alipidbilayerihproteihecell，withspecializedsitesforattaduniwithneighbcells.
Ribosomes（R）—numerous（millionsperaesthatassembleproteins.
Vadvesicles（V）—avarietyofmembraments，whichfulfllspecializedfunparticularcells
speitodria，forexample，produergyforallofthecell’sactivitiesfromthebreakdownoffoodmoleanimalcells.Plantiquelyhavechloroplasts，whivertsunlightandtosugarsasaneoitodria.Bothmitodriaandaythemselveshavebeenfree-livinganismsearlyiion，beforebealyier，plexcell.Everycellhasa‘blueprint’foritsowioheDNAofitsgenes.Inanyparti，theDNAinformatiohesameiype，whethertheyarebrain，gut，orskiatictaintwocopiesofeaAmolecule（theyaresaidtobediploid），exceptthegermlinecells（eggsandsperm）inwhiAexistsasasihesegermlinecellsarehaploid）.ermfusetoproducethefirstbryo（thezygote），twocopiesoftheDored.HowtheDofhaplcellsisreducedwillbedisChapter4.
IheDNAiscirdlieshients，butinplantandaisedwithinananelleknownasthenuLatin nucula，‘littleisfoldedintoes.Cellswithermedeukaryotes（aGreekword，meaning‘trueker’），rokaryreek，‘beforenuts’）suchasbacteriahaverelativelylittlespecializatioentsiernalanelles.
Allcellsreproducethemselvesbysplittingintotwo.Setoiheirtsrapidlyenoughtodivisionbyaproasbinaryfissioninaslittleas20mihemuchlargereukaryotecellsmay takethebestpartofadaytodoubletheirsizebeforedivision.Cellsasmaeshaveanunparalleledeffianddiversityofpohebasigblocksofcellareproteinmoledeverycellhastensofthousandsofdifferentproteins，inmillionsofcopies.Aumbersofthevariousmoleaeukaryoticcellareextremelydifficulttoquantify，butestimatesdoexistforbacteria，whichhave40%oftheirvolumemadeupofaroundonemillionmoleculesofsolubleproteins.Avarietyoffivemillionsmallmoleculesatfor3%，thenDNA2%.Thecellmembraerbacterialcell20%，andtheremaihetsaremadeupofthemolecularmaeededtosyeins，ing2000ribosomes.Thesefiguresberoughlyscaledup1000-foldfortheinvolumeofanimalandplantcells，whitainhundredsofindividualanellessuchasmitodria，andaroundtenmillionribosomes.Ribosomesaresmallmolecularmaesthatprovidefortheassemblyofein，acrucialrequiremeeheprovisioeinpriortocelldivision.
Itishardtofindman-mademaerythatmatchesthewsecell.Perhapsthebiggestsuperputerohwouldeclose，butitwouldalsoytophysicallyreproduceitselfwithfasterandfasterprocessors.Whilethismaysouatement，itbeorereasonablewhenyousiderthatcellshavehadaroundfourbilliettheiracttogether，tlydriveingpressuresofion.Ierms，ioifacelladaptstoitse，feedsandreproduitsurvives，butfailuremeahisprocesshasproducedaself-propagatiainingandrepairifunswithalevelofefficyrarelyapproachedbyman-mademaery.Muchoftheeofnanoteology—theengineeringoffunalsystemsatamolecularscale—isaimedatrepliolecularreaswiththeefficylevelsfoundinlivingcells.Aswellastheirhighlyeffitmetabolism（life-sustaiivity），cellsarealsocapableuuralrigidity，asfouhatgivewood，palms，andbamboovaluesofmeiaareexalinas（skystheFarEastoftenuselocalbambooratherthansteelsg）.
Tissuesaion
Themaiicofeukaryoticcellsistheirabilitytoaltertheirshape，pos，aabolismtofulfllaparticulartask—todifferentiate—afacilitywhitoetogetherandformmulticellulartissues，tobiissuesintans，andthenformaireanismsuchasahumanbeing.Weareformedfromaround200differenttypesofcellsthefourmaihelia（surfaectivetissue（blood，bone，andcartilage），muservoustissue.Cellsareproducedatwidelydifferentrates，fromsperm（atarateof1000iimeasaheartbeat）toamaysurvivealifetime.Someofourbloodcellssurvivefhthourswhereastheredcellscirculateforabout120days.
Asanexampleofdifferentiation，webrieflysiderthosecellsthatformourbarriertotheehecellsatthesurfaceofourskinhaveundergoneamajor‘remodelliion）tobeeeocytes，whicharefiattenedpolygonalplatesmademaihesameproteinthatmakesnails，hair，ahersinbirds）.Eaeodsaboutadayatthesurface，befshedaheohatwepresentanewlayerofskiheworldeverydayofourlives.Theshedcellsarereplacedbydivisionofuhatdiffereheypassupwardsthroughthe24celllayersthatmakeuptheoverallthianskihetoplayerofeocyteseffitlyremovesaccumulateddebris，alongwiththe7.5millionbacteriapersquaretimetreandthevariousfungalgrowthsthattlyattempttoizeouroutersurfaces.Thereare1000eocytespersquaremillimetre，andouroverallskinsurfaceareaisjustuwosquaremetres，leadingtoadailyloss（a）ofaroundtwothousandmillioncellseachday.
Theshedskincellsmakeupabout60%ofhouseholddust，andthoseweloseinbedprovidethedailybreadofthemillionorsodustmitesthatliveinourmattresses.Notallpartsofourbodiesarereplacedatthisrate，buttheskin，an，providesagoodexampleofthebasicpropertiesofcells—repli，divisioioasafunalpartofatissue，andultimatelydeath.
Aresingle-ssimple?
Instarktrasttothesinglepurposeiaskincellaspiresto，weshouldsiderwhatlifeislikefle-celledeukaryaheyaresmall，theycouldbesidered‘simple’and‘primitive’.Tosurvive，however，theyfood，mailees，reprodudavoidbeiheranisms.Protozoaarethelargestgroupofsingled-imalserhapsthemostfamiliar.AmoebaehavebeeopursueandcatchotherprotozoasuchasParamecium—perhapstheunicellularequivalentofaliongazebra.Possiblyeveillareagroupofprotozoaoria.Theseunissudroetesparadoxusdoheirfoodbutiachthemselvestovarioussurfadtheirtentadwaitforsomeuozoan，suchasaParamecloseby.Iftheteouched，the‘prey’isinstantlyparalysed，asofitsbodyaresuthetehebodyofthesu，redugthepreytoashrivelledhuskinamatterofmimethodforthetransferofpreytsisunknown，butitisdriveaculararraysoficstructurescalledmicrotubulesioriaacles（see Figure 6c;microtubuleswillbedesChapter2）.Havinghadagoodmeal，suayate’，aprtheattaodifiedteoeachhwhichtheyexuclei（theyhaveone‘maudthreesmallones）.Ifbingeingaeeshasanfacility.Deeslivesattachedtothegillplatesof Gammarus，afreshwatershrimp. Gammarusmularly，sothatDeesrisksbeibehiyshell，losiflowofwaterillplatesahisbrings.However，Deesreizestheearlieststagesofmoulting（possiblybyrespondingtomoultinghormone），aamorphosesintstruownasciliawhichallowsitto‘upstidfiofgillplates（ciliawillbedesChapter2）.Thus，‘simple’single-shavejustasplexalifestyleasthatfoundinmanymultis.
Althoughprotozoa（andsis）mustihtheireosurvive，theirperislargelylimitedtophysidchemiterasattheirmembrawithsfeatures.Insissuchasthegreenalgae onas，a’isvisiblewithinthechloroplastumicroscope.Theeyespotisaplexsandwibrahrowsofgraaround200differentproteins，ingthesamerhodopsinsfouinaofourowneye.Signalsfromthephotoreceptiveeyespotcausetheflagella（whip-liketailsonthesurfaceofthealgae）tobeatiways，sothealgaeswimthterlight，butawayfromlightthatistht.Whilsttheeyespotmightbethoughtofasarudimehereisnoimaginginvolved，orrequired，astheeyespotsuppliesalltheinformatioheanism’stoight（）rhythms，andoptimizephotosyivity.
Tissueculture
Anenormousamountofinformationaboutmammaliancellshas invitrostudies;cellsgrowninaglassorplasticflask，maintainedihat37degreesinanatmosphereof5%dioxide，repligthesinthebodyascloselyaspossible.Plantalsobecultured，oftenwiththeircelledoff.Growthofdtissuesoutsidethebodygoesbackasfarasthelate19thtury，ahodologyfortissueaurewasestablishedbyRossHarrisoninBaltimore，USAaround1910.Tissuessugfromlaboratorymiceembryosusuallygrowwellassingleing‘primarycultures’，buttheyalmostalwayshavealimitedlifespan，dyingoffafter50orsoroundsofcelldivisioareisolatedfromsolidtissuesrequireattattothesurfaceoftheplasticgrowthvesseltodivideandgrow，butbloodcells，whiallyexistinaliquid，doadgroension’culture.Cellsareusuallyculturedasasimixedcellculturessuchasthosegrownfromisolatedbonemarrowwillbothsurviveandmaintainthecellulariionsthatothebody.ieceofsolidtissueisexdputintocultures，thecellsthatgrowthemostreadilyarethosethatrespondtowoundinginthelivinganimal.Theseownasfibroblasts，arethecellsthatmaintaiissuethatformsthestructuralframeworkofthebody，suchasligamentsandtendons.Afterinjury，fibroblastspulltheedgesofwouher，ahethatformsscartissue.Iionstheyarelongandthin，withaleadifansoutatthefrontofthecellasitmrowingsurface（Figure 3c）.Withinafewdays，uousroundsofcelldivisiohesurfaceoftheflasktobeeinglycrowded，ahereisnomoreroomfornewlydividedcellstoreattachtsurface，divisiohisissity-depeinhibitionofgrowth，andischaracteristialcells，butnotthosecellsderivedfromtumours.Atthispointthecellsaresub-culturedintonewflasksataredusity.Becauseprimaryculturesdieoffafterabout50divisions，thisputsatimelimitonanyseriesofexperiments，so‘perma’es（usuallyderivedfromtumours）whichdivideielyareoftenpreferredbyresearchers.
&ypesandtheirshape.（a）Haemopoieticell（spherical），（b）epithelial（polygonal）cell，（c）fibroblast，（d）adipocyteorfatcell.Allthesecellshavebeengrowniure.Althoughthesurfaceofthefatcellissmooth，theothercellsaremoretypical，withmembranefolds，ruffles，andfiensions（microvilli）overtheirsurfaces.Thedifferensizebetweedanormalcellisshownbytherouhebottomleft.（e）DeesparadoxusfeedingonaParameciumattachedtoitstentacles
HeLacells，thefirstpermahumane
Althoughpermaesfromhumansaregenerallyderivedfromtumours，tumourbiopsiesarenotoriouslytrickytoestablishihabout1issuccessful.Thefirsttimethathumancellsweregrownincultureasapermaewasin1951，byGeeyinBaltimore，USA.ThesewereHeLacells，socalledbecauseoftheirsource—acervicaltumourbiopsyfromaladyriettaLarietta’swasdiagnosedinJohnsHopkiheveryfewhospitalsintheUSAin1951thatwouldtreatamemberoftheblackpopulationwithouthealthihetime，althoughourbiopsieseretlyputintocultures，nonewerthanafewdays.Hea’scells，hantodoublewithindays，sadlyiheextremelyaggressiveandfastgrowingtumthroughoutherbody，whichkilledherwithinmonths.Thea’scellsveryquicklyspreadaroundtheworldofcellbiology.Iheworldwidedemapermahumane，theTuskegeeInstitutebeganmassprodugthecells，shipping20，000tubesor6trillioncellseveryweek.Thismeansthateveryfewmonths，thesamevolumeofcellsthathadbeeoformHeaherselflefttheprodue.HeLacellswereexperimentedonineveryceivableway，noneofwhichossibleusing‘whole’humans.Theywereexposedtthatmightbetoxiours，everytypeofradiationpossible，aoxinsahemostparttheydidinasignifitlydifferentwaytodifferentspealiaitortanttoshowthathumaurecellsdidnotbehaveinanyuniqueways.Ashercellshavenowbeengroideforoverhalfatury，thereisprobablyenoughofHeheflecells）aroundtheworldforhertopopulateherowntown.Infaehters，afterseeingthefilmJurassicPark，wasbrieflycedthattherewere‘otherinLondon，whereshehadreadthatmuchresearchhadbeeonHeLarietta’swouldprobablyneverhaveknownabouttheirmother’scellsexceptthattheyweretrabyJohnsHopkinsresearcherswhowaoparetheDNAfromHeLacellswithitsanmatch.Thisiedthemtothemultimilliondollarindustrythathadbeeheirmother’stumour，and，notunreasoheirlawyers）triedtoextrathesituation.Uhem，in1951nhtstopatieed，aeofiahassubseque‘aperson’sdiscardedtissuesarenottheirpropertyandercialized’.Evea’sarestilluoaffordhealthiheUSA.Despite60yearsofintensivereseargreAanalysis，theactualreasonsfortheprolifiatureofHeLacellgrowtharestillunknown.HeLaostbesideredthe‘weeds’oftissueculture，havingtakeheresbyatalination，afaetolightwhenculturedcellsbegaerizedbytheirDNAsome2o.
Fordecades，researedonvitrohasbeeioojusthowrepreseis，becauseallyinathree-dimensionaleinamanismatoavarietyofstressesandfaotexperiencedbyasinglelayerofcellsgrolasticdish.Remarkably，inoverhalfaturyoftratedresearch，culturehaveproducedverylittleinthewayofmisleadinginformation，andwithoutthisaccumulatedkisuhetpotentialofstemantherapywouldexistatall.
本章未完，请点击下一章继续阅读！若浏览器显示没有新章节了，请尝试点击右上角↗️或右下角↘️的菜单，退出阅读模式即可，谢谢！