《微生物学》双语教学授课教案参考模板范本

PAGEPAGE31《微生物学》双语教学授课教案iculardisease.Koch’spostulates：Koch'spostulatesareanumberofcriteriathathavebeenusedinthepasttoprovethatabacteriumisresponsibleforaparticulardisease.Thebacteriashouldbefoundinallcasesandatallsitesofthedisease.Thebacteriashouldbeisolatedfromtheinfectedpersonandmaintainedinpureculture.Thepureculturedmicrobeshouldcausesymptomsofthediseaseoninoculationintoasusceptibleindividual.Thebacteriashouldbereisolatedfromtheintentionallyinfectedhost.Theimportanceofmicrobiology：microbesinourbodyEveryonehasmicroorganismsinandonthebodySomemicroorganismsliveinhumansandotheranimalsandareneededtomaintaintheanimalshealth.thesemakeupthenormalflora（正常菌群）;SomeMicroorganismscausedisease.Thedisease-producingpropertiesofaspeciesofmicrobeandthehost'sresistanceareimportantfactorsindeterminingwhetherapersonwillcontractadisease.2.MicrobesandHumanWelfareMicroorganismsdegradedeadplantsandanimalsandrecyclechemicalelementstobeusedbylivingplantsandanimals.BacteriaareusedtodecomposeorganicmatterinsewBioremediationprocessesusebacteriatocleanuptoxicwastes.Bacteriathatcausediseasesininsectsarebeingusedasspecificforthepestanddonotharmtheenvironment.UsingrecombinantDNA,bacteriacanproduceimportanthumanproteins,suchasinsulin,beta-endorphin,andhepatitisBvaccine.Microorganismscanbeusedtohelpproducefoods.Theyarealsofoodsources(single-cellprotein)them3.Asabasicbiologicalscience：microorganismsarethebestmodelsystemsforunderstandingbasiclifeprocesses.Allcellshavemuchincommon,whatistrueforE.coliisalsotrueforelephant,onlymoresoSimpleyetrepresentativeEasinessandquicknesstogrowlargequantityCommoncharacterizesofmicroorganism•Bigsurface/volume•Highabsorptionandtransformation•Rapidgrowthandreproduction•Easinesstovariation••highadaptationtoenvironment•Diversityquestion1.Matchthefollowingpeopletotheircontributiontowardtheadvancementofmicrobiology. (a)Firsttoobservebacteria (b)Firsttoobservecellsin Hooke plantmaterialandname_Koch them Lister (c)Disprovedspontaneous Pasteur generation VanLeeuwenhoek(d)ProvedthatmicroorganismscancausediseaseDiscoveredpenicillinUsedthefirstsyntheticchemotheraputicagentFirsttoemploydisinfectantsinsurgicalprocedures Matchthefollowingmicroorganismstotheirdescriptions. (a)Notcomposedofcells (b)Cellwallmadeofchitin Fungi (c)Cellwallmadeof Protozoom peptidoglycan (d)Cellwallmadeofcellulose;photosynthetic(e)Complexcellstructurelackingacellwall3.Brieflystatetheroleplayedbymicroorganismsineachofthefollowing.BiologicalcontrolofpestsRecyclingofelementsNormalfloraSewagetreatmentHumaninsulinproduction4Themicrobeswerefirstformallyobservedinthemid-1600's,butthecelltheorywasn'tenunciateduntil1839.WriteabriefessayexplainingwhymicrobiologydidnotbecomeaformallyrecognizedscienceuntilPasteur'stime.5.CompareandcontrasttheworksofLouisPasteurandRobertKoch,intermsofbothappliedandbasicscience.6.Microorganismscanbebothbeneficialandharmfultohumans.Althoughwetendtoemphasizetheharmfulmicroorganisms(infectiousdiseaseagents),manymorearebeneficialthanharmful.●Inwhatwaysaremicroorganismsimportantinthefood,agriculture,andindustries?7.LouisPasteur´sworkonspontaneousgenerationledtothedevelopmentofmethodsforcontrolofthegrowthofmicroorganisms.RobertKochdevelopedcriteriaforthestudyofinfectiousmicroorganisms,anddevelopedthefirstmethodsforthegrowthofpureculturesofmicroorganisms.BeijerinckandWinogradskystudiedbacteriainsoilandwater,anddevelopedtheenrichmentculturetechnique.Inthetwentiethcentury,basicandappliedmicrobiologyhaveworkedhandinhandtoyieldanumberofimportantpracticaladvancesandarevolutioninmolecularbiology.●HowdidPasteur´sfamousexperimentdefeatthetheoryofspontaneousgeneration?●HowcanKoch´spostulatesprovecauseandeffectinadisease?●Whowasthefirstpersontousesolidculturemediainmicrobiology?●Whatadvantagesdosolidmediaofferforthecultureofmicroorganisms?●Whatistheenrichmentculturetechniqueandwhywasitausefulnewmethodinmicrobiology?Chapter2prokayoticmicroorganism(原核微生物)第二章原核微生物prokaryoticcellsThechiefdistinguishingcharacteristicsofprocaryoticcellsare:geneticmaterial(DNA)isnotenclosedwithinamembrane.Theylackothermembraneboundedorganelles.TheirDNAisnotassociatedwithhistoneproteins(specialchromosomalproteinsfoundineucaryotes).Theircellwallsalmostalwayscontainthecomplexpolysaccharidepeptidoglycan（肽聚糖）.Bacteria(细菌)andarchaeobacteria（古细菌）Bacteriaaresmall,single-celled,microorganismsthatbelongtoagroupcalledprokaryotes.Bacteriaareubiquitous.Theyareahighlysuccessfulanddiversegroupoforganismsthatcanobtainenergyandcarbonfromawiderangeofsourcesandthereforecancolonizeeverynicheonourplanetfromdeepoceantrenchestovolcaniccraters.Inthe1970s,usingDNAsequencinginformation,itwasfoundthatthegroupweknowasthebacteriacouldbesplitintotwo,theeubacteriaandthearchaeobacteriaanditappearsthatthesetwogroupsevolvedawayfromeachotherveryearlyinthehistoryoflivingthingsataboutthesametimethatthefirstgroupofeukaryoticcellsevolved.MembersoftheeubacteriaincludesomeofthemorefamiliarbacteriasuchasEscherichiacolt（大肠埃希氏菌）andStaphylococcusaureus（金黄色葡萄球菌）andaretheprokaryotesthatarebeststudiedandunderstood.Thearchaebacteriaareaverydiversegroupoforganisms,whichdifferfromtheeubacteria（真细菌0inanumberoffeatureshaving,inparticular,verydifferentcellwallsandmembranes.ThisgroupincludesbacteriathatarecapableofexistinginextremeenvironmentsSize,Shape,andArrangementofMostbacteriaarefrom0.20to2.0/µmindiameterandfrom2to8µminlength.Thethreebasicbacterialshapesarecoccus(spheres),bacillus(rods),andspiral(twisted).Inadditiontothethreebasicshapes,therearestar-shapedcells(genusStella)andrecentlydiscoveredsquare,flatcells(halophilic(嗜盐的)archaeobacteria)andtriantheshapeofabacteriumisdeterminedbyheredity.However,anumberofenvironmentalconditionscanalterthatshape.Pleomorphic(多型性的)bacteriacanassumeseveralshapes.GramStain：TheeubacteriaarefrequentlydividedintotwogroupsonthebasisoftheirreactiontoastaindevisedbyChristianCramin1884.Thedifferentialreactiontothestainingprocedureisbecauseofthestructureofthecellwallinthesetwogroupsofbacteria.Gram-positivebacteriahaveasinglemembranecalledglycan(20-80nm).TheGram-negativebacteriahaveonlyathinlayerofpeptidoglycan(1-3nm)butontheoutsideofthisthereisafurtheroutermembranewhichactsasanadditionalbarrier.TheprocedurefortheGramstainisasfollows.Fixedcellsarestainedwithadarkstainsuchascrystalviolet,followedbyiodinewhichcomplexeswiththestaininthecellwallofthebacteria.Alcoholisadded,whichwashesthedarkstainofcrystalviolet-iodineoutofceilsthathavethincellwallsbutnotfromthosethathavethickcellwalls.Finally,apalerstainsuchascarbolfuschin,calledacounterstain,isaddedwhichstainsthedecolorizedcellspinkbutisnotseenonthedarkstainingcellsthatretainedthefirststain.Thecellsthatretainthestain(withthickcellwalls)arecalledGram-positiveandappeardarkpurpleunderlightmicroscopy.Theonesthatlosethestain(withthincellwallsandanoutermembrane)arecalledGram-negativeandstainpinkorpalepurpleThecellwallsurroundstheplasmamembraneandprotectsthecellfromchangesinosmoticpressure（渗透压）andprovidesrigidityandstrength.Thebacterialcellwallconsistsofpeptidoglycan（肽聚糖）,apolymerconsistingofNAGandNAMandshortchainsofaminoacids.Gram-positive（革兰氏阳性）cellwallsconsistofmanylayersofpeptidoglycanandalsocontainteichoicacids（垣酸）.Gram-negative（革兰氏阴性）bacteriahavealipidprotein-lipopolysaccharide-phospholipidoutermembranesurroundingathinpeptidoglycanlayer.Theoutermembraneprotectsthecellfromphagocytosisandpenicillin（青霉素）,lysozyme（溶菌酶）,andotherchemicals.Porins（孔蛋白）areproteinsthatpermitsmallmoleculestopassthroughtheoutermembrane;specificchannelproteinsallowothermoleculestomovethroughtheoutermemThelipopolysaccharide（脂多糖，LPS）componentoftheoutermembraneconsistsofsugarsthatfunctionasantigensandlipidA,whichisanendotoxin（内毒素）.teichoicacid:teichoicacid,madeupofglycerolorribitoljoinedbyphosphategroups.D-Ala,glucoseorsugarsmaybeattachedtotheglycerolorribitolandthepolymersareattachedeitherdirectlytotheNAMinthepeptidoglycanortolipidsinthemembrane(inthiscasetheyarecalledlipoteichoicacids).Thefunctionofthesemoleculesisunclearbuttheymayhavearoleinmaintainingthestructureofthecellwallandinthecontrolofautolysis.periplasmicspace（周质空间）TheoutermembraneofGram-negativebacteriaactsasanadditionalbarrierprotectingthepeptidoglycanfromtoxiccompoundssuchaslysozymewhichactonthecellwall.Itcreatesanaqueousspacebetweenthetwomembranescalledtheperiplasmicspacewhichisthoughttohaveagel-likestructurewithaloosenetworkofpeptidoglycanrunningthroughit.Estimatesastothewidthofthepeptidoglycanvaryfrom1-71nmbutithasprovedtobedifficulttoobtainarealdefinitivevalue.Theperiplasmicspacecontainsarangeofproteinsassociatedwith:transportofnutrientsintothecell;enzymesthatareinvolvedinnutrientacquisitionsuchasproteases;enzymesthatdefendthecellagainsttoxicchemicalssuchasв-lactamasesthatdestroypenicillin.outermembraneTheoutermembraneofGram-negativebacteriaismadeupofphospholipidsbutitalsocontainssomeuniquefeaturesPoresformedbyproteinscalledporinssuchasOmpFandOmpCthatallowthepassivediffusionofsmallmoleculesintotheperiplasmicspace.AnabundantsmalllipoproteincalledBraun'slipoproteinthatiscovalentlyboundtothepeptidoglycanandisembeddedintheoutermembranebyitshydrophobiclipid,thereforeholdingthepeptidoglycanandoutermembraneclosetogether.LPSmoleculesarefoundintheouterleafletoftheoutermembraneprojectingintothesurroundingmedium.Mycoplasma（支原体）isabacterialgenusthatnaturallylackscellArchaeobacteriahavepseudomurein（假肽聚糖）;theylackpeptido.lformsaremutantbacteriawithdefectivecellwalls.ArchaeobacterialcellwallsOneofthedistinctivefeaturesofarchaebacteriaisthenatureofthelipidsintheplasmamembranewhich,unliketheester-linkedlipidsofeubacteriaandeukaryotesareether-linkedtoglycerol.Theyarealsolongchainedandbranched.Archaebacterialcellwallsandenvelopesshowgreatdiversityandcomplexityinstructure.TheydonotcontainpeptidoglycanalthoughsomedohaveasimilarcompoundcalledpseudomureinwhichcontainsN-acetyl-typeofcellwallistheS-layer,atwo-dimensional,paracrystalline,arrayofproteinorglycoproteinonthecellsurface.Othershavethickpolysaccharidewallsoutsidetheirplasmamembrane. peptidoglycanusedtobeatargetforantimicrobialagentsthatdestroyprokaryoticcellsspecifically,butdonotharmeukaryoticcells;anexampleofthisistheantibioticpenicillin(TopicF7).Lysozyme,anaturalantibacterialagentfoundintearsandnaturalsecretions,breaksdownthelinkagebetweenNAMandNAG.Removalofthecellwallunderconditionswheretheosmolarityofthemediumisthesameastheinsideofthecell(isotonicsolution)resultsintheformationofroundprotoplasts(原生质体)(Gram-positives)orspheroplasts(球形体)(Gram-negatives)whichsurviveaslongastheisotonicityismaintained.Thesestructureslyse,however,ifplacedinadiluteInthepresenceoflysozyme,gram-positivecellwallsaredestroyedandtheremainingcellularcontentsarereferredtoasaprotoplast.Inthepresenceoflysozyme,gram-negativecellwallsarenotcompletelydestroyedandtheremainingcellularcontentsarereferredtoasaspheroplast.Protoplastsandspheroplastsaresubjecttoosmoticlysis.Antibioticssuchaspenicillininterferewithcellwallsynthesis.Theplasmamembraneenclosesthecytoplasmandisaphospholipidbilayerwithprotein(fluidmosaic).mostofbacterialackofsteriol（固醇）Theplasmamembraneisselectivelypermeable.Plasmamembranescarryenzymesformetabolicreactions,suchasnutrientbreakdown,energyproduction,andphotosynthesis.Mesosomes—irregularinfoldingsoftheplasmamembrane—arenowconsideredartifacts.Plasmamembranescanbedestroyedbyalcoholsandpolymyxin.Cytoplasmisthefluidcomponentinsidetheplasmamembrane.Thecytoplasmismostlywater,withinorganicandorganicmolecules,DNA,ribosomes,andinclusions.Thecytoplasmofaprocaryotecontainsnumerous70Sribosomes;ribosomesconsistofrRNAandprotein.Proteinsynthesisoccursatribosomes;thiscanbeinhibitedbycertainantibiotics.Inclusions（内含物）arereservedepositsfoundinprocaryoticandeucaryoticcells.Amongtheinclusionsfoundinbacteriaaremetachromaticgranules（异染粒）(inorganicphosphate),polysaccharidegranules(，多糖，usuallyglycogenorstarch),lipidinclusions（脂滴）,sulfurgranules（硫粒）,carboxysomes(，羧酶体，ribulose1,5-diphosphatecarboxylase),andgasvacuoles（气泡）.1.ThenuclearareacontainstheDNAofthebacterialchromosome.Bacteriacanalsocontainplasmids,whichareextrachromosomalDNAcircles.capsuleorslimelayercapsule（荚膜）orslime（黏液层）layerisagelatinouspolysaccharideand/orpolypeptidecovering.Capsulesmayprotectpathogensfromphagocytosis（吞噬）.Capsulesprovideadherencetosurfaces,preventdesiccation,andmayprovidenutrients.Flagella（鞭毛）arerelativelylongfilamentousappendagesconsistingofafilament,hook,andbasalbody.Procaryoticflagellarotatetopushthecell.Motile（运动）.bacteriaexhibittaxis（趋性）—positivetaxisismovementtowardanattractantandnegativetaxisismovementawayfromarepellent.Ffimbriae（菌毛）andpili（性毛）areshort,thinappendages.Fimbriaehelpcellsadheretosurfaces.PilijoincellsforthetransferofDNAfromonecelltoanother.Endosporesarerestingstructuresformedbysomebacteriaforsurvivalduringadverseenvironmentalconditions.Theprocessofendosporeformationiscalledsporulation;thereturnofanendosporetoitsvegetativestateiscalledgermination.Endosporesareamethodassurvival,notoneofreproduction.Certainbacteriawillformasporewithintheircellmembrane(anendospore)thatallowsthemtowaitoutdeterioratingenvironmentalconditions.Certaindiseasecausingbacteria(suchastheonethatcausesthediseaseAnthrax)canbevirulent(capableofcausinganinfection)1300yearsafterformingtheirendospore!）BACTERIALDIVISIONThenormalreproductivemethodofbacteriaisbinaryfission,inwhichasinglecelldividesintotwoidenticalSomebacteriareproducebybudding.,aerialsporeformation,orfragmentation.binaryfission（二分裂）Themethodbywhichbacteriareproduce.ThecircularDNAmoleculeisreplicated;thenthecellsplitsintotwoidenticalcells,eachcontaininganexactcopyoftheoriginalcell'sDNA.Actinomycetesarefilamentous,gram-positivebacillithatformabranchingmycelium.Cyanobacteria（蓝细菌）：Blue-greenbacteria;unicellularorfilamentouschainsofcellsthatcarryoutphotosynthesis.existintwoforms:theelementarybody,whichistheformbodysecretions,andthereticulatebody,whichmultipliesyoungadultsandasthmatics.Althoughmostspeciesareparasitic,mycoplasmascanbeculturedoncomplexartificialmedia.Theyareconsideredmembraneparasitesbecausetheybindtightlytoepithelialliningsoftherespiratoryandurogenitaltracts.systemicinfectionbysuppressingtheimmunesystem.question Diagrameachofthefollowingflagellararrangements:LophotrichousMonotrichousPeritrichous Endosporeformationiscalled Itisinitiatedby__.Formationofanewcellfromanendo..Thisprocessistriggeredby3.Drawthebacterialshapeslistedina,b,andc.Showhowd,e,andfarespecialconditionsofa,b,andc, (d)Spirochete (e)Streptobacilli Listthreedifferencesbetweenprocaryoticandeucary5.Matchthestructurestotheirfunctions.CellwallEndosporeFlagellaPlasmamembraneA:ProtectionfromosmoticA:ProtectionfromosmoticAttachmentC:ProtectionfromphagocytesD:RestingE:ProteinsynthesisF:SelectivelypermeableI:Transferofgeneticmaterial Ofwhatvalueiseachofthefollowingtothecell?MetachromaticgranulesPolysaccharidegranulesLipidinclusionsSulfurgranulesCarboxysomesGasvacuolesWhyisanendosporecalledarestingstructure?Ofwhatadvantageisanendosporetoabacterialcell?Compareandcontrastthefollowing:ProtoplastsandspheroplastspenicillinandlyzosomeFlagellaandfimbriaerickttsiaeandchlamydias9.Answerthefollowingquestionsusingthediagramsbelow,whichrepresentcrosssectionsofbacterialcellWhichdiagramrepresentsagram-positivebacterium?Howcanyoutell?ExplainhowtheGramstainworkstodistinguishbetweenthesetwotypesofcellwalls.Whydoespenicillinhavenoeffectonmostgramnegativecells?HowdoessentialmoleculesentercellsthrougheachLipoproteinPeptidoglycanCellmembranePeptidoglycanCellmembrane10.Whycanprocaryoticcellsbesmallerthaneucaryoticcellsandstillcarryonallthefunctionsforlife?11.Twotypesofprocaryoticcellshavebeendistinguished:eubacterialandarchaeobacterial.Howdothesecellsdifferfromeachother?Howaretheysimilar?12.WhatistheevolutionaryadvantageofthemonolayeroftenfoundinArchaealmembranes?13.Bacillussubtilisisacommonsoilbacterium.WhatgenusdoesB.subtilisbelongto?14.Althoughprokaryotesandeukaryotesaredistinguishedbynuclearstructure,otherimportantdifferencesexistbetweenthesetwocelltypes.Prokaryotesaresmallerinsizethaneukaryotes,andeukaryotescontainamembrane-enclosednucleusandorganelleswithinwhichmanyimportantfunctionsarecarriedout.Thesmallsizeofprokaryoticcellsaffectstheirphysiology,growthrate,andecology.●Listthreemorphologicaltypesofprokaryotes.●Whatisaflagellum,andwhatdoesitdo?●Whatphysicalpropertyofcellsincreasesascellsbecomesmaller?15.ThecellwallsofBacteriacontainapolysaccharidecalledpeptidoglycan.ThismaterialconsistsofstrandsofalternatingrepeatsofN-acetylglucosamineandN-acetylmuramicacid,withthelattercross-linkedbetweenstrandsbyshortpeptides.Archaealackpeptidoglycanbutcontainwallsmadeofotherpolysaccharidesorofprotein.Theenzymelysozymedestroyspeptidoglycan,leadingtocelllysis.●Listthemonomericcomponentsofpeptidoglycan.●Whyispeptidoglycansuchastrongmacromolecule?●Howdoespsuedopeptidoglycanresemblepeptidoglycan?Howdothetwomoleculesdiffer?●Howisaprotoplastgenerated?16.Inadditiontopeptidoglycan,Gram-negativeBacteriacontainanoutermembraneconsistingoflipopolysacchaaride,aprotein,andlipoprotein.Proteinscalledporinsallowforpermeabilityacrosstheoutermembrane,andaspacecalledtheperiplasmispresent,whichcontainsvariousproteinsinvolvedinimportantcellularfunctions.●WhatcomponentsconstitutetheLPSlayerofGram-negativeBacteria?●Whatisthefunctionofporins,andwherearetheylocatedinaGram-negativecellwall?●WhydoesalcoholreadilydecolorizeGram-negativebacteria?17.TheendosporeisahighlyresistantdifferentiatedbacterialcellproducedbycertaintypesofGram-positiveBacteria.Sporeformationleadstoanearlydehydratedsporecorethatcontainsessentialmacromoleculesandavarietyofsubstances,suchascalciumdipicolinateandsmallacid-solubleproteins,absentfromvegetativecells.Sporescanremaindormantindefinitelybutgerminatequicklywhentheappropriatetriggerisapplied.●Whatisdipicolinicacid,andwhereisitfound?●WhatareSASPs,andwhataretheirfunctions?●Whathappenswhenanendosporegerminates?chapter3eukaryoticmicroorganisms第3章真核微生物EukaryotecellAtypeofcellfoundinmanyorganismsincludingsingle-celledprotozoomandmulticellularfungi,plants,andanimals;characterizedbyamembrane-boundednucleusandothermembraneousorganelleseukaryoticcellsconstructAppendages(cilia,flagella),glycocalyx,cellwall,cytoplasmic(orcell)membrane,ribosomes,organelles(nucleus,nucleolus,endoMaincharactersticofeukaryticcellsThenucleus,whichcontainsDNAintheformofchrolelmembranesinthecytoplasm,calledtheendoplasmicreticulum.Theendoplasmicreticulumprovidesasurfaceforchemicalreactions,servesasatransportingnetwork,andstoressynthesizedmolecules.805ribosomesarefoundinthecytoplasmorattachedtotheendoplasmicreticulum.TheGolgicomplexconsistsofcisternae.Itfunctionsinsecretion,carbohydratesynthesis,andglycoproteinformation.MitochondriaaretheprimarysitesofATPproduction.Theycontainsmall70SribosomesandDNA,andtheymultiplybyfission.Chloroplastscontainchlorophyllandenzymesforphotosynthesis.Likemitochondria,theycontain70SribosomesandDNAandmultiplybyfission.LysosomesareformedfromGolgicomplexes.Theystorepowerfuldigestiveenzymes.Apairofcylindricalstructurescalledcentriolesthatareinvolvedincelldivisionarenearthenucleus.Bothflagellaandciliacontaina"ninepairs+twopairs"arrangementofmicrotubules.Fungiamongtheterrestrialfungi,givenwithsexualsporetype,areZygomycota（接合菌纲）(ascospores，子囊孢子),Basidiomycota（担子菌纲）(basidiospores，担孢子),andDeuteromycota（半知菌纲）YeastYeastcellwallsconsistofglucanandmannan.plasmamembranescontaincarbohydratesattachedtotheproteinsandsterolsnotfoundinprokarvacuolars(液泡).buddingisthemainreproductionstyleofyeast.ascospore.MoldsHyphaeofmoldsHyphaecanalsobeclassifiedaccordingtotheirparticulariblemassofgrowththatappearsonthesurfaceofasubstrateandpenetratesittodigestandabsorbnutrients.Duringthedevelopmentofafungalcolony,thevegetativehyphaegiverisetostructurescalledreproductive,oraerialhyphae（繁殖菌丝）,whichorientvertifortheproductionoffungalreproductivebodiescalledspores.Themainmaterialoffungalcellwallsischitin.AsexualSporeidentified,butwewillconsiderthethreemostcommon:zyformsasporangium.MeiosisofdiploidcellsofthesporangiumChapter4VIRUSES第四章病毒Avirusisasubmicroscopicinfectiousparticlecomposedofaproteincoatandanucleicacidcore.Viruses,likecells,carrygeneticinformationencodedintheirnucleicacid,andcanundergomutationsandreproduce;however,theycannotcarryoutmetabolism,andthusarenotconsideredalive.Virusesareclassifiedbythetypeofnucleicacidtheycontain,andtheshapeoftheirproteincapsule.ofVirusesDependingonone'sviewpoint,virusesmayberegardedasexceptionallycomplexaggregationsofnonlivingchemicalsorasexceptionallysimplelivingmicrobes.Virusescontainasingletypeofnucleicacid(DNAorRNA)andaproteincoat,sometimesenclosedbyanenvelopecomposedoflipids,proteins,andcarbohydrates.Virusesareobligatoryintracellularparasites.Theymultiplybyusingthehostcell'ssynthesizingmachinerytocausethesynthesisofspecializedelementsthatcantransfertheviralnucleicacidtoothercells.Avirionisacomplete,fullydevelopedviralparticlecomposedofnucleicacidsurroundedbyacoat.HOSTHostrangereferstothespectrumofhostcellsinwhichaviruscanmultiply.Dependingonitshostrange,avirusisgenerallyclassifiedasananimalvirus,bacterialvirus(bacteriophage),orplantvirus.Aviruscaninfectonlycertainspecieswithineachclass.Hostrangeisdeterminedbythespecificattachmentsiteonthehostcell'ssurfaceandtheavailabilityofhostcellularfactors. Viralsizeisdeterminedbyfiltrationthroughmembranefilters,ultracentrifugation,andelectronmicroscopy.Virusesrangefrom20to300nmindiameter.NUCLEICACID Theproportionofnucleicacidinrelationtoproteininvirusesrangesfromabout1%toabout50%.VirusescontaineitherDNAorRNA,neverboth,andthenucleicacidmaybesingle-ordouble-stranded,linearorcircular,ordividedintoseveralseparatemoleCAPSIDANDENVELOPE Theproteincoatsurroundingthenucleicacidofavirusiscalledthecapsid（衣壳）.Thecapsidiscomposedofsubunits,thecapsomeres（衣壳粒）,whichcanbeasingletypeofproteinorseveraltypes.Thecapsidofsomevirusesisenclosedbyanenvelopeconsistingoflipids,proteins,andcarbohydrates.Someenvelopesarecoveredwithcarbohydrate-proteincomplexescalledspikes（刺突）.Viruseswithoutenvelopesarecallednakedviruses.GENERALMORPHOLOGY Helical（螺旋对称）viruses(forexample,tobaccomosaicvirus)resemblelongrods,andtheircapsidsarehollowcylinderssurroundingthenucleicacid.Polyhedral（多面体）viruses(forexample,adenovirus，腺病毒)aremanysided.Usuallythecapsidisanicosahedron（二十面体）.Envelopedvirusesarecoveredbyanenvelopeandareroughlysphericalbuthighlypleomorphic（多型性的）.Therearealsoenvelopedhelicalviruses(forexample,influenzavirus)andenvelopedpolyhedralviruses(forexample,herpessimplexvirus).manybacteriophageshaveapolyhedralcapsidwithahelicaltailattached.TaxonomyofVirusesmorphologicalclass,sizeofcapsid,andnumberofcapsomeres.Otherclassificationschemestakeintoaccountthevilogicalproperties,siteofmultiplication,andmethodoftransmission.Isolation,Cultivation,andIdentificationofViruses Virusesmustbegrowninlivingcells.Theeasiestvirusestogrowarebacteriophages.GROWTHOFBACTERIOPHAGESINTHELABORATORYteriaandnutrientagar.Afterseveralviralmultiplicationcycles,thebacteriaintheareasurroundingtheoriginalvirusaredestroyed;theareaoflysisiscalledaplaque.asplaque-formingunits.THELABORATORY CultivationofsomeanimalvirusesrequireswholeaniSomeanimalvirusescanbecultivatedinembryonatedCellculturesarecellsgrowinginculturemediainthelaboratory.