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Download Viruses, Viroids, Prions and Parasites Differentiate a virus from a
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TopicNine:Viruses,Viroids,PrionsandParasites Differentiateavirusfromabacterium Generalcharacteristicsofviruses: • Obligatoryintracellularparasites–theycanonlyfunctioninsidea livingcell.Whenoutsidealivinghostcelltheyareinert.Once insidealivinghostcelltheviralnucleicacidsbecomeactiveand viralmultiplicationresults. • Containasingletypeofnucleicacid,eitherDNAorRNA(butnot both). • Containaproteincoatthatsurroundsthenucleicacid. • Someareenclosedbyanenvelopethatcanbeeitherhostderived orvirusderived. • Multiplyinsidelivingcellsbyusingthesynthesizingmachineryof thecell. • Someviruseshavespikes. • Mostvirusesinfectonlyspecifictypesofcellsinonehost.(havea hostrange) • Causethesynthesisofspecializedstructuresthatcantransferthe viralnucleicacidtoothercells. • Muchsmallerthanbacteria(20-1000nm). • Listthepropertiesofanenveloped&non-envelopedvirus Virion:acomplete,fullydeveloped,infectiousparticleofavirus. • ConsistsofeitherDNAorRNA(NEVERBOTH). • Coveredinacapsid,madeupofproteinsubunitscalled capsomeres.(Thecapsidislikeacoat,andthecapsomereislike patchesonthecoat.) • Canbecoveredinanenvelope(maybehostcellderived). Envelopedvirusesareroughlyspherical. • Spikesmayprotrudefromtheenvelope. • Thecapsidofanon-envelopedvirusprotectsthenucleicacidfrom enzymesinbiologicalfluidsandpromotesthevirus’sattachment tosusceptiblehostcells. • InHelicalvirusesthenucleicacidisfoundwithinahollow cylindricalcapsidthathasahelicalstructure. Describethestructureofacomplexvirus • Bacterialviruses(bacteriophagesorphages)areoftencomplex viruses. • Bacteriophagemeans“bacteriaeating.” • TheycanputspecificDNAintobacterialcells. • Haveacomplexvirionstructureincluding: o Head o Sheath o Baseplate o Tail Defineviralspecies • Aviralspeciesisagroupofvirusessharingthesamegenetic informationandecologicalniche(hostrange). • Specificepithetsarenotused.Virusspeciesaredesignatedby descriptivecommonnames.Theseareusefulbecausethey describethevirusinamoreunderstandableway. • Familynamesendin–viridae • Genusnamesendin–virus. • Subspeciesaredesignatedbyanumber(egH1N1) Giveanexampleofafamily,genus,andcommonnameforavirus Herpesviridae Herpesvirus Humanherpesvirus Describehowbacteriophagearecultured • Virusesmustbegrowninlivingcells. • Bacteriophagesaregrowneitherinsuspensionsofbacteriain liquidmediaorinbacterialculturesonsolidmedia. • Bacteriophagesformplaquesonalawnofbacteria. • Theplaqueisaclearingonthebacteriallawncausedbythelysisof abacterialcolony. • Eachplaquetheoreticallycorrespondstoasinglevirusinthe initialsuspension. Describehowanimalvirusesareculturedandtheirgrowthcurve Animalvirusesmaybegrowninthelaboratoryinthreeways: 1. Inlivinganimals 2. Inembryonatedeggs:needafertilizedeggwhichhasactively dividingcellstoallowviralgrowth.(usedtomakesomevaccines). 3. Cellcultures:nowthepreferredtypeofgrowthmediumformany viruses. ViralGrowthCurvesaredifferenttobacterialgrowthcurves.Theviruses gointothecellsandmultiplyandthenoncetherearenocellslefttoinfect, theystopgrowth.ItiscalledaViralOne-StepGrowthCurve.
