CellStructureChapter3ExamplesofCells3.2What,Exactly,IsaCell?CellsarethefundamentalunitsofalllifeAllcellsstartlifewithaplasmamembrane,cytoplasm,andaregionofDNAwhich,ineukaryoticcellsonly,isenclosedbyanucleusCellStructureAplasmamembranesurroundsthecellandcontrolswhichsubstancesmoveinandoutPlasmamembraneAcell’soutermostmembraneLipidbilayerStructuralfoundationofcellmembranes;mainlyphospholipidsarrangedtail-to-tailinabilayerCytoplasmAnimportantpartofhomeostasisismaintainingthecompositionofcytoplasm,whichdiffersfromfluidoutsidethecellCytoplasmSemifluidsubstanceenclosedbyacell’splasmamembraneOrganellesCellmetabolismoccursincytoplasmandinternalcompartments,includingorganellesOrganelleStructurethatcarriesoutaspecializedmetabolicfunctioninsideacellProkaryotesandEukaryotesCellsareclassedaseukaryotesorprokaryotesbasedonhowDNAishousedinthecell

NucleusOrganellewithtwomembranesthatholdsaeukaryoticcell’sDNANucleoidRegionofcytoplasmwhereDNAisconcentratedinaprokaryoticcellTheCellTheoryCelltheoryisthefundamentaltheoryofbiologyCelltheoryAllorganismsconsistofoneormorecellsThecellisthesmallestunitoflifeEachnewcellarisesfromanothercellAcellpasseshereditaryinformationtoitsoffspring3.3MeasuringCellsMostcellsarevisibleonlywiththehelpofmicroscopesDifferenttypesofmicroscopesuselightorelectronstorevealdifferentdetailsofcellsBacteriaontheTipofaPinBacteriaarethesmallestandsimplestcells“AnimalculesandBeasties”Nooneknewcellsexisteduntilmicroscopeswereinvented1600s:vanLeeuwenhoek’smicroscopeHooke,Schleiden,andSchwann1600s:RobertHookeimprovedthemicroscopeandcoinedtheterm“cell”1839:MatthiasSchleidenandTheodoreSchwannrealizedcellswerealiveandproposedthecelltheory3.4TheStructureofCellMembranesTheplasmamembraneisbasicallyalipidbilayerballoonfilledwithfluidThenonpolartailsofbothlayersaresandwichedbetweenthepolarheadsTheFluidMosaicModelAcellmembraneisamosaicofproteinsandlipids(mainlyphospholipids)thatfunctionsasaselectivelypermeablebarrierthatseparatesaninternalenvironmentfromanexternaloneFluidmosaicmodelAcellmembranecanbeconsideredatwo-dimensionalfluidofmixedcompositionMembraneProteinsProteinsassociatedwithamembranecarryoutmostmembranefunctionsTransportproteinspassivelyoractivelyassistspecificionsormoleculesacrossamembraneEnzymesspeedchemicalprocessesAdhesionproteinshelpcellssticktogetherRecognitionproteinstagcellsas“self”Receptorproteinsbindtoaparticularsubstanceoutsidethecell3.5IntroducingProkaryoticCellsDomainsBacteriaandArchaeamakeuptheprokaryotesProkaryotesaresingle-celledorganismswithnonucleus,butmanyhaveacellwallandoneormoreflagellaorpili3.6APeekInsideaEukaryoticCellAlleukaryoticcellsstartlifewithanucleus,ribosomes,organellesoftheendomembranesystem(includingendoplasmicreticulum,vesicles,Golgibodies),mitochondria,andotherorganellesTheNucleusPores,receptors,andtransportproteinsinthenuclearenvelopecontrolthemovementofmoleculesintoandoutofthenucleusNuclearenvelopeAdoublemembranethatconstitutestheouterboundaryofthenucleusTheEndomembraneSystemTheendomembranesystemincludesroughandsmoothendoplasmicreticulum,vesicles,andGolgibodiesEndomembranesystemSeriesofinteractingorganellesbetweenthenucleusandplasmamembraneMakesandmodifieslipidsandproteinsRecyclesmoleculesandparticlessuchasworn-outcellparts,andinactivatestoxinsTheEndomembraneSystemEndoplasmicreticulum(ER)AcontinuoussystemofsacsandtubesthatisanextensionofthenuclearenvelopeRoughERisstuddedwithribosomes(forproteinproduction)SmoothERhasnoribosomesTheEndomembraneSystemVesicleSmall,membrane-enclosed,saclikeorganelleStores,transports,ordegradesitscontentsPeroxisomeEnzyme-filledvesiclethatbreaksdownaminoacids,fattyacids,andtoxicsubstancesLysosomeVesiclewithenzymesforintracellulardigestionTheEndomembraneSystemGolgibodyOrganellethatmodifiespolypeptidesandlipidsSortsandpackagesthefinishedproductsintotransportvesiclesVacuoleAfluid-filledorganellethatisolatesordisposesofwastes,debris,ortoxicmaterialsMitochondriaandChloroplastsMitochondriaandchloroplastshavetheirownDNA–theyresemblebacteriaandmayhaveevolvedbyendosymbiosisMitochondrionDouble-membranedorganellethatproducesATPChloroplastOrganelleofphotosynthesisTheCytoskeletonCytoskeletonDynamicnetworkofproteinfilamentsthatsupport,organize,andmoveeukaryoticcellsandtheirinternalstructuresThecytoskeletoninteractswithaccessoryproteins,suchasmotorproteinsCiliaandFalseFeetCiliaShort,hairlikestructuresthatprojectfromtheplasmamembraneofsomeeukaryoticcellsCoordinatedbeatingstirsfluid,propelsmotilecellsMovedbyorganizedarraysofmicrotubulesExample:clearsparticlesfromairwaysFlagellaEukaryoticflagellaarewhiplikestructuresthatpropelcellssuchasspermthroughfluidDifferentinternalstructureandmotionthanprokaryoticflagellaFalseFeetPseudopod(falsefoot)Extendablelobeofmembrane-enclosedcytoplasmformovementortoengulfpreyMovedbymotorproteinsattachedtomicrofilaments