细胞结构 Cell Structure

1CellStructureChapter52CellTheory•Allorganismsarecomposedofoneormorecells.•Cellsarethesmallestlivingunitsofalllivingorganisms.•Cellsariseonlybydivisionofapreviouslyexistingcell.3CellCharacteristics•Geneticmaterial–singlecircularmoleculeofDNAinprokaryotes–doublehelixlocatedinnucleusineukaryotes–nuclearenvelope(doublemembrane•Cytoplasmfillscellinterior––sugars,aminoacids,–proteins-organelles•Plasmamembraneencloses–thecell–phospholipidbilayerPhospholipidMembraneproteins4GeneralizedEukaryoticCell5CellSize•Mostcellsarerelativelysmallbecauseassizeincreases,volumeincreasesmuchmorerapidly.–longerdiffusiontime6VisualizingCells•Resolution-minimumdistancetwopointscanbeapartandstillbedistinguishedastwoseparatepoints–Compoundmicroscopes-magnifyinstagesusingmultiplelenses–Transmissionelectronmicroscope-electronstransmittedthroughspecimen–Scanningelectronmicroscope-electronsbeamedontosurfaceofthespecimen7VisualizingCells8ProkaryoticCells•Simplestorganisms–Cytoplasmissurroundedbyplasmamembraneandencasedinarigidcellwallcomposedofpeptidoglycan.nodistinctinteriorcompartmentsgram-positive–thicksinglelayerwallthatretainsavioletdyefromGramstainproceduregram-negative–multilayeredwalldoesnotretaindyeSusceptibilityofbacteriatoantibioticsdependsoncellwallstructure.9ProkaryoticCells•Someuseflagellumforlocomotion–threadlikestructuresprotrudingfromcellsurfaceBacterialcellwallFlagellinRotarymotorSheath10EukaryoticCells•Characterizedbycompartmentalizationbyanendomembranesystem,andthepresenceofmembrane-boundorganelles.–Centralvacuole–plants,storage–Vesicles(smaller)–Chromosomes-DNAandprotein–Cytoskeleton(internalproteinscaffolding)–Cellwalls–plantsandfungi111213Nucleus•Repositoryforgeneticmaterial•Directsactivitiesofthecell•Usuallysingle,somecellsseveral,RBCnone–Nucleolus-regionofintensiveribosomalRNAsynthesis•Surfaceofnucleusboundbytwophospholipidbilayermembranes–nuclearmembrane–Nuclearpores–proteingatekeepersUsuallyproteinsgoinginandRNAgoingout14Nucleus15Chromosomes•DNAofeukaryotesisdividedintolinearchromosomes.–existasstrandsofchromatin,exceptduringcelldivision–associatedwithpackaginghistones,packagingproteinsnucleosomes16EndomembraneSystem•Compartmentalizescell,channelingpassageofmoleculesthroughcell’sinterior.–EndoplasmicreticulumRoughER-studdedwithribosomesSmoothER-fewribosomes17Endoplasmicreticulum•Largestinternalmembrane•ComposedofLipidbilayer•Servesassystemofchannelsfromthenucleus•Functionsinstorageandsecretion•RoughERis“rough”becauseofassociatedribosomes(sitesofproteinsynthesis•SmoothER-lackassociatedribosomes–containedembeddedenzymes,catalyzesynthesisofcarbohydrateandlipidmolecules18EndomembraneSystem•Golgiapparatus–collectionofGolgibodiescollect,package,anddistributemoleculessynthesizedatonelocationinthecellandutilizedatanotherlocationFront-cis,Back–transCisternae–stackedmembranefolds19VesiclebuddingfromroughendoplasmicreticulumFusionofvesiclewithGolgiapparatusMigratingtransportvesicleProteinProteinsTransportvesicleGolgiapparatusCisternaeRibosometransfacecisfaceCopyright©TheMcGraw-HillCompanies,Inc.Permissionrequiredforreproductionordisplay.20EndomembraneSystem•Vesicles–Lysosomes-membrane-boundvesiclescontainingdigestiveenzymes–fromGolgi–Microbodies-enzyme-bearing,membrane-enclosedvesicles.Peroxisomes-containenzymesthatcatalyzetheremovalofelectronsandassociatedhydrogenatomsPeroxisome–namedforhydrogenperoxideproducedasaby-productEnzymebreaksdowntowaterandoxygen21CytoplasmPhagocytosisFoodvesicleGolgiapparatusLysosomesPlasmamembraneDigestionofphagocytizedfoodparticlesorcellsEndoplasmicreticulumTransportvesicleOldordamagedorganelleBreakdownofoldorganelleExtracellularfluidCopyright©TheMcGraw-HillCompanies,Inc.Permissionrequiredforreproductionordisplay.22Ribosomes•RibosomesareRNA-proteincomplexescomposedoftwosubunitsthatjoinandattachtomessengerRNA.–siteofproteinsynthesis–assembledinnucleoli23OrganellesWithDNA•Mitochondria–boundedbyexteriorandinteriormembranes–interiorpartitionedbycristae•Chloroplasts–haveenclosedinternalcompartmentsofstackedgrana,containingthylakoids–foundinphotosyntheticorganisms24MitochondriaA.Powerhouseofthecell-cellularmetabolismB.Structure-outerandinnermembranes,cristaeC.HavetheirownDNA25Chloroplasts•Chloroplastsarelargerandmorecomplexthanmitochondria•Grana–closedcompartmentsofstackedmembranes•Thylakoids–discshapedstructure–lightcapturingpigment•Stroma–fluidmatrix26Endosymbiosis•Endosymbiotictheorysuggestsengulfedprokaryotesprovidedhostswithadvantagesassociatedwithspecializedmetabolicactivities.27TheoryofEndosymbiosis28Evidencefortheendosymbionttheoryisthatmitochondriaandchloroplasts:-Areappropriatesizetobedescendantsofeubacteria.-Haveinnermembranessimilartothoseonprokaryoticplasmamembranes.-Replicatebysplitting,asinprokaryotes.-DNAiscircularanddifferentfromtheDNAofthecell'snucleus.-ContaintheirowncomponentsforDNAtranscriptionandtranslationintoproteins.-Haveribosomessimilartoprokaryoticribosomes.-Molecularsystematicslendevidencetosupportthistheory.-Manyextantorganismsareinvolvedinendosymbioticrela