Medical Microbiology

7 GeneralVirology

K.A.Bienz

Definition

&VirusesarecomplexesconsistingofproteinandanRNAorDNAgenome.

Theylackbothcellularstructureandindependentmetabolicprocesses.They

replicatesolelybyexploitinglivingcellsbasedontheinformationintheviral

genome. &

Virusesareautonomousinfectiousparticlesthatdifferwidelyfromother

microorganismsinanumberofcharacteristics:theyhavenocellularstruc-

ture,consistingonlyofproteinsandnucleicacid(DNAorRNA).Theyhaveno

metabolicsystemsoftheirown,butratherdependonthesyntheticmecha-

nismofalivinghostcell,wherebythevirusesexploitnormalcellularmeta-

bolismbydeliveringtheirowngeneticinformation,i.e.,nucleicacid,intothe

hostcell.Thehostcellacceptsthenucleicacidandproceedstoproducethe

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Table 7. 1 EssentialCharacteristicsofViruses

Size 25 nm(picornavirus)to 250! 350 nm(smallpoxvirus).Resolving

powerofalightmicroscope: 300 nm,bacteria: 500 – 5000 nm.The

comparativesizesareillustratedinFig. 7. 1.

Genome DNAorRNA.Double-strandedorsingle-strandednucleicacid,

dependingonthespecies.

Structure Virusesarecomplexescomprisingvirus-codedproteinand

nucleicacid;someviralspeciescarrycell-codedcomponents

(membranes,tRNA).

Reproduction Onlyinlivingcells.Thevirussuppliestheinformationinthe

formofnucleicacidsandinsomecasesafewenzymes;thecell

providestheremainingenzymes,theproteinsynthesizing

apparatus,thechemicalbuildingblocks,theenergy,andthe

structuralframeworkforthesyntheticsteps.

Antibiotics Virusesareunaffectedbyantibiotics,butcanbeinhibitedby

interferonandcertainchemotherapeuticagents.

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Kayser, Medical Microbiology © 2005 Thieme