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Chapter2UniformityandDiversityofthecellLearningObjectives1.Lookbrieflyatthehistoryofcelltheory;2.Considerthebasicpropertiesofcells;3.Comparesomecharacteristicsoftwodifferentclassesofcells:prokaryotesandeukaryotes;4.Comprehendaspeciallife:viruses1.TheCellTheory:ABriefHistoryIn1665,RobertHookesawanetworkoftinyboxlikecompartmentsthatremindedhimofahoneycomb.ThenHecalledtheselittlecompartmentscellulae,aLatintermmeaninglittleroom.Itisfromthiswordwegetourpresent-dayterm,cell.ThemicroscopeusedbyRobertHookeandthehoneycomb-likenetworkofcellhedrawedin1665ThediscoveryofcellsfollowedfromtheinventionofthemicroscopeCelltheoryhasthreebasictenets:1.Allorganismsarecomposedofoneormorecells.2.Thecellisbasicunitofstructureandfunctionforallorganisms.3.Allcellsariseonlyfrompreexistingcellsbydivision.2.Whyarecellsthebasicunitsoflife?A.Thecellisthestructuralunitoflife,Allorganismsismakeupofcells.B.Thecellisthefunctionalunitoforganisms.Allmetabolicactivityisbasedoncells.C.Thecellisthefoundationofreproduce,andthebridgeofinheritance.Thecellpossesscommongeneticlanguage.D.ThecellisthegrowinganddevelopingbasisoflifeHumanfetaldevelopment.(a)At5weeks,limbbuds,eyes,theheart,theliverandrudimentsofallotherorganshavestartedtodevelopintheembryo,whichisonlyabout1cmlong.(b)Growthanddevelopmentoftheoffspring,nowcalledafetus,continueduringthesecondtrimester.Thisfetusis14weeksoldandabout6cmlong.(c)Thefetusinthisphotographis20weeksold.Nowthefetusgrowstoabout30cminlength.E.Cell(nucleus)istotipotent,whichcancreateaneworganismofthesametypeAsageneralrule,thecellsofamulticellularorganismallcontainthesamesetofgenes.Foranimals,thefirstevidencethatevenhighlyspecializedcellcarryafullcomplementofgeneswasverifiedbytheexperimentoftadpolenucleitransplantingintounfertilizedeggthathadbeendeprivedofitsownnucleus.Somecandevelopswimmingtadpoles.Thisisanimalcloning.Anespeciallydramaticexampleofanimalcloningwasreportedin1997.Dollythefirstanimaleverclonedfromacellderivedfromanadult.DollyandherdaughterTheprocessofcloningDollyIsthereanypracticalvaluetosuchtechnology?F.Cellisend-resultoflifeoriginandfundationoforganismevolutionG.Nocell,Nofulllife.Virus:Euvirus(virus):DNAorRNAandproteinscomplexViroid:TheinfectiveRNAconstitute,discoverGrowabout20remainingsVirusof朊(prion):infectiveproteins3.BasicpropertiesofcellsA.Cellsarehighlycomplexandorganized,capableofself-regulation;B.Cellsacquireandutilizeenergy.C.Allcellssharesimilarstructure,compositionandmetabolicfeatures:Plasmamembrane,DNA/RNA,andRibosome.D.Cellscancapableofproducingmoreofthemselves,evengrowandreproduceincultureforextendedperiods.HeLacellsareculturedtumorcellsisolatedfromacancerpatientnamedHenriettaLacksin1951.Itisthefirsthumancelltobekeptincultureforlongperiodsoftimeandisstillusedtoday.JohnsHopkinsunivesity,in1951E.Cellsareabletorespondtostimuliviasurfacereceptorsthatsensechangesinthechemicalenvironment.Cellswithinplantoranimalrespondtostimulilessobviouslythansingle-celledprotist.Buttheyrespond.Theypossesreceptorsthatinteractwithsubstancesintheenvironmentinhighlyspecificways.Forexample,thereceptoronthecellsurfacecanrespondtohormonesandgrowthfactors.5.TheSizeofCellsa)diameterb)MeasuredinunitsofCellmicrometers:1um=10-6meternanometers:1nm=10-9meterc)Cellsizeislimited:nucleus/cytoplasmratio;surfacearea/volumeratio;substancescanefficientlytravelthroughthecytoplasmviadiffusion.几种显微镜观察样品大小的范围6.Twofundamentallydifferentclassesofcells:ProkaryotesandeukaryotesA.Prokaryoticandeukaryoticcellsaredistinguishedbythesizeandthetypesofinternalstructures,ororganelles,especiallyifthereisnuclearenvelope.Bacteriaareprokaryotes,theyarose3.5billionyearsago;Protists,fungi,plants,andanimalsareeukaryotes.Thefirsteukaryotesarose1.5billionyearsago.B.Characteristicsthatdistinguishprokaryoticandeukaryoticcells(1)Complexity:Prokaryotesarerelativelysimple,eukaryotesaremorecomplexinstructureandfunctionpp.36Table2-2;2-3真核细胞与原核细胞基本特征的比较特征原核细胞真核细胞细胞膜核膜染色体核外DNA胞质区域化细胞骨架核糖体细胞增殖有（行使多种功能）有无有裸露DNA，无组蛋白DNA与组蛋白结合含有质粒DNA线粒体与叶绿体DNA简单（无细胞器）复杂有各种细胞器无有（MT、MF、IF）70S型（30S和50S）80S型（40S和60S）无丝分裂有丝分裂、减数分裂真核细胞与原核细胞的遗传结构装置和基因表达的比较特征原核细胞真核细胞遗传信息量基因组DNA重复序列内含子RNA聚合酶DNA复制转录与翻译加工与修饰表达调控小大n2n环状、裸露DNA线形、染色体罕见大量存在无有一种复合体三种：polⅠ、Ⅱ、Ⅲ无明显周期性有明显周期性（S期）同时、同地先转录（核）后翻译（质）无有复杂的加工过程操纵子形式多层次、多环节特征动物细胞植物细胞有无质体（叶绿体）有无细胞壁有无大的中央液胞细胞膜离子泵营养吸收无，异养营养有，自养营养无有（纤维素和果胶质）无有（代谢调节作用）钠-钾ATP酶质子ATP酶Na+驱动共运转H+驱动共运转植物细胞与动物细胞的比较(2)Geneticmaterial:AllCellsStoreTheirHereditaryInformationintheSameLinerChemicalCode(DNA)a.Packaging:Prokaryoteshaveanucleoidregionwhereasekukaryotehaveatrue,membrane-boundnucleus.b.Amount:Eukaryoteshaveseveralordersofmagnitudemoregeneticmaterialthanprokaryotes.c.Form:EukaryoteshavemanychromosomesthataremadeofbothDNAandproteinwhereasprokaryoteshaveasingleDNAchromosomea.Packaging:Prokaryoteshaveanucleoidregionwhereasekukaryotehaveatrue,membrane-boundnucleus.(bacterinm:0.25-3.0mm,toencodebetweenseveralhundredandseveralthousandproteins,Thesimplestknowncellshavejustunder500genes).b.Amount:Eukaryoteshaveseveralordersofmagnitudemoregeneticmaterialthanprokaryotes.(yeast:4.6mmDNA,encod