Demonstration
Viral Lysis and Budding
Educator Materials
VIRALLYSISANDBUDDING
OVERVIEW
Thisactivityispartofaseriesofactivitiesanddemonstrationsfocusingonvariousaspectsofthehuman
immunodeficiencyvirus(HIV)lifecycle.Inthisactivity,studentslearnhowvirusesleaveahostcellbyeitherlysisor
budding.
Viruses,atypeofinfectiousagent,cancausediseaseineukaryoticandprokaryoticorganisms,includinganimals,plants,
fungi,orbacteria.Someviruses(adenovirus,Norwalkvirus,orpapillomavirus)arecharacterizedas“nonenveloped”or
“naked.”Theseviruseshaveatypicalviralstructureofanucleicacidcoresurroundedbyaproteincoat(capsid).Other
viruses(influenza,hepatitisA,Ebola,orHIV)arecharacterizedas“enveloped.”Theseviruseshavethetypicalviral
structure,buttheyhaveanadditionalcoatcomprisedofproteinsandlipidsderivedfromthemembraneoftheinfected
hostcell.
Studentswillexploreaninteractivethatdiscussessomeofthecharacteristicsofviruses.Theywillthenobservetwo
demonstrationsthatillustratehowvirusesexitcells.Envelopedvirusesexitacellbybudding,takingthehostcell
membranewiththem.Inthefirstdemonstration,thisprocessisshownusingaplasticbagfilledwithStyrofoamballsor
PingPongballs.Nonenvelopedvirusesexitaninfectedcellbylysis,orbyburstingoutofanddestroyingtheinfectedcell.
Intheseconddemonstration,thisprocessisshownusingaballoonfilledwithbitsofpaper.
Thisactivitycanbedoneonitsownorfollowingsomeoftheotheractivitiesintheseries,suchastheintegrationactivity
orthereversetranscriptionactivity.
KEYCONCEPTSANDLEARNINGOBJECTIVES
• Virusesexithostcellsbyeitherlysisorbudding.
• Throughbudding,partofthehostcellmembranebecomespartofthevirus.
• Lysisdestroysthehostcell.
Studentswillbeableto:
• explainthedifferencebetweennonenvelopedvirusesandenvelopedviruses.
• describetwostrategiesthatvirusesusetoexitinfectedcells.
• evaluatethelimitationsofmodelstoillustratebiologicalprocesses.
CURRICULUMCONNECTIONS
Curriculum
NGSS(2013)
APBiology(2013)
Standards
HS.LS1-1
2.B.3;2.D.3;3.A.1;3.C.3;4.A.1
KEYTERMS
Virus,enveloped,nonenveloped,protein,genome,capsid,lysis,budding,host,eukaryotic
TIMEREQUIREMENT
Thisactivityisdesignedtobecompletedina50-minuteclassperiod.
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Demonstration
Viral Lysis and Budding
Educator Materials
SUGGESTEDAUDIENCE
Thisactivityisappropriateforalllevelsofhighschoolbiology(Honors,AP,andIB).
PRIORKNOWLEDGE
Studentsshouldknowthatvirusesinfectcellsandreplicatewithinhostcellstoproducemoreviruses.Itwouldbe
helpfulforstudentstobefamiliarwiththebasicstructureofcells,includingknowingthatanimalcellsaresurroundedby
alipidmembraneembeddedwithproteins.
MATERIALS
Demonstration1:BuddingbyEnvelopedVirus
• LargeZiplocbag(1gallon)torepresentthehostcell
• 4to8Styrofoamballs(orPingPongballs)torepresentvirusparticles
• 4to8rubberbandstowrapatintervalsaroundtheindividualStyrofoamballsinsidethebag
• Scissors
Demonstration2:LysisbyNonenvelopedVirus
• Largeballoon(8”to12”)torepresentthehostcell
• Cut-uppiecesofpapertorepresentvirusparticles.Thepiecesofpapermustbesmallenoughtoinsertintothe
balloon.Youcanalsouseconfetti.
• Funnel(optional)toinsertthepiecesofpaperintheballoon.Ifafunnelisused,besurethattheneckiswide
enoughforthesmallpiecesofpapertofitthroughbutsmallenoughtofitintothemouthoftheballoon.
• Pintopoptheballoon
PROCEDURE
1.Reviewstudents’answerstoquestions1to6intheirworksheet.
2.Explainthatyouwillmodelhowanenvelopedvirusexitsacell.CarryoutstepsatodbelowasshowninFigure1.
Demonstration1:BuddingbyEnvelopedVirus
a.PlaceasingleStyrofoamballinaplasticbag.ThisstepmodelsaviruslikeHIVinfectingacell.
b.Insidethecell,theviruswillreplicate.Addthreetosevenadditionalballstoillustratethisstep.
c.OnceHIVhasreplicatedandnewvirusparticlesform,theywillbudfromthecellsurface,takingbitsofthehostcell
membranewiththem.Toillustratethisstep,wraptheplasticaroundeachballandkeepitinplacewitharubberband.
Makesuretherubberbandistight.
d.Cutthebagbelowtherubberbandsandreleasetheballs.Callattentiontothefactthateachballiscoveredwitha
sectionoftheplasticbag.
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Demonstration
Viral Lysis and Budding
Educator Materials
Figure1.Modelofhowanenvelopedvirusbuddingfromahostcell.
3.WatchtheanimationoftheHIVlifecycleathttps://www.hhmi.org/biointeractive/hiv-life-cycle.Discusswithstudents
thedifferencesbetweenthismodelandhowHIVactuallyexitsfromacell.Showstudentsthatthereareholesinthe
Ziplocbagwherethescissorswereusedtocutoffthebuddingvirus.Whenvirusesbudfromcells,thecellmembrane
closesaroundwheretheviruswas,sothereisn’taholeinthecellmembrane(atleastnotatfirst;oncethousandsof
viruseshavebud,thenalotofthemembranegetsusedupandmaydevelopholesasthecelldies).
4.Tellstudentsthatyouwillnowmodelhowanonenvelopedornakedvirusexitsfromacellbyaprocessknownas
lysis.CarryoutstepsatodbelowasshowninFigure2.
Demonstration2:LysisbyNonenvelopedVirus
a.Cutuppiecesofpaper.Youwillneedabout100piecesofpaperforagoodeffect.Besuretocutthepapersmall
enoughtoeasilyslipthroughtheneckoftheballoon.Thisshouldbedonebeforeclass.(Notethatyoucanalsouse
confettiforthisdemonstration.)Staticelectricitymaycausethesmallpiecesofpapertobecomeattractedtothe
balloon(bothinsideandout).Positionthepileofcutpiecesawayfromtheballoonsothattheydonotbecomeattracted
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Demonstration
Viral Lysis and Budding
Educator Materials
butcloseenoughforyoutogatherseveralatatime.
b.Insertthepiecesofpaperintheballoon.Afterinsertingafew,gentlyblowintotheballoontomovethepiecesoutof
theneckbeforeaddingmore.
c.Afteraddingatleast100piecesofpaper,finishblowinguptheballoonandknotitshut.Then,giveitacoupleof
shakes.
d.Holdtheballoonhighupoverstudents’headsandpopitusingthepin.Makecertaintogeteveryone’sattention
whenyouarereadytopoptheballoon.Ithappensveryquicklyandthepiecesscatterquiteadistance.
Figure2.Modelofhowanonenvelopedvirusexitsacellbylysis.
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Demonstration
Viral Lysis and Budding
Educator Materials
TEACHINGTIPS
• Studentscancompletethestudenthandoutquestions1-6forhomeworkbeforeclassorinclass.Students
shouldexploredifferenttypesofviralstructureandhowvirusescausediseasebyusingtheHHMIinteractive
“VirusExplorer”(https://www.hhmi.org/biointeractive/virus-explorer)toinvestigatethedifferenttypesof
viruses.Studenthandoutquestions4-6arebasedonthisonlineresource.
• Question9inthehandoutrequiresstudentstocalculaterelativesize.Dependingonthelevelofyourstudents,
youmaywanttohavethemworkonthequestionasaclassexercise.
• Afterthefirstdemonstration,studentsareaskedtowatchananimationoftheviruslifecycle.Ifstudentshave
doneanyotheractivitiesinthisseries,theywillhavealreadyseenthisanimationandyoumayjustskiptothe
sectionattheendwhereHIVbudsfromthecell.Explainthatthemembraneismadeprimarilyoflipidsand
closesbackupwhenthevirusisreleased.
• Thisactivityprovidesanopportunitytodiscussthelimitationsofmodels.Onelimitationinthefirstmodelisthat
thebuddingseemstoimplythatholesareleftinthecellmembraneasthevirionsexit,whichisnotaccurate.
Alsotherelativesizesofthevirusparticlesandcellsarenotaccurate.Modelsarehoweverusefulinillustrating
generalconcepts,suchasthekeydifferencesbetweenlysisandbudding.
•
Reviewwithstudentsthedifferencesbetweenlysisandbudding.Buddingdoesnotcausecompletedestruction
ofthehostcell,meaningitcontinuestoproducemoreviruses.Eachnewlysynthesizedvirusnowhaspartofthe
hostcell’smembranearoundit,forminganenvelope.Becausethevirusisenvelopedinthehost’scell
membrane,itismoredifficultforimmunecellstorecognizethevirusandeliminateit(althoughthehost’s
antibodiescanbindtoviralproteinsembeddedintheenvelope).Ontheotherhand,becausenonenveloped
virusesdonothaveacellmembranearoundthemtheyaremoreresistanttoheat,acids,anddrying.
Nonenvelopedvirusescanpersistonsurfaces,forexample,foralongertime.
ANSWERKEY
1.Listthreetofivedistinguishingcharacteristicsofviruses.
Answerswillvary,butstudentsmaysaythatvirusesaretiny,arenotcomposedofcells,cancausedisease,infect
cells,andareparasites.Studentsinmoreadvancedclassesmaysaythatvirusesconsistofgeneticmaterial(DNAor
RNA)andproteinsandthattheyreplicateusinghostcellproteins.Studentsmayalsosaythatvirusesarenot
consideredtobelivingorganisms.Somemayalsomentionthatinfectionscausesbyvirusescannotbetreatedwith
antibiotics.
2.Listthreetofivedistinguishingcharacteristicsoflivingorganisms.
Answerswillvary,butstudentsmaysaythatlivingorganismspossessacellmembraneandgeneticmaterial,havethe
capacitytoconvertanduseenergy(ATP),andareabletoreproduceontheirown(whichisgoodforfurther
discussion,asnotalllivingorganismscansuccessfullyreproduce).Alivingorganismundergoesbirthanddeath.While
alive,itcarriesoutmetabolicactivitiesandgeneratesthemoleculesnecessaryforlife.Theycangrowbyincreasingin
sizeand/ornumber.Studentsmayalsomentionthatlivingorganismsexcreteexcesssubstancesandthewaste
productsofmetabolism.
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Demonstration
Viral Lysis and Budding
Educator Materials
3.Provideevidencefromyouranswersabovetosupportaclaimthat
a.virusesarelivingorganisms.
Studentsmaymentionthatvirusesareabletoreproduceandsomeviruseshaveacellmembrane.Theycontain
geneticmaterial
b.virusesarenotlivingorganisms.
Virusesarenotabletoreproduceontheirown.Theyarealsounabletocollectanduseenergyontheirown.
4.Listthreecharacteristicsusedtoclassifydifferenttypesofviruses.
Studentsshouldmentionstructure,typeofgeneticmaterial,theorganismsitinfects,andwhetherithasanenvelope.
5.Whatisaviralenvelope?Wheredoesitcomefrom?
Theviralenvelopeisamembranethatsurroundssometypesofviruses.Itcomesfromthehostcell’smembrane.
6.Selectoneenvelopedandonenonenveloped(naked)virusandthencompletethechartbelow.
Virusname
Shape
Enveloped
Genome
Which
Doesitcause
(YesorNo)
(DNAorRNA)
organism(s)does disease?
itinfect?
InfluenzaA
spherical
Yes
RNA
Humans,pigs,
Yes
othermammals,
andbirds
papillomavirus icosahedral No
DNA
Manydifferent
Sometypesyes,
organisms
includingcancer
7.a.Inthisdemonstration,whatrepresentsthevirusparticles?
TheStyrofoamballsarethevirusparticles.
b.Whatrepresentsthehostcell?
Theplasticbagrepresentsthehostcell.
8.Whenanewvirusparticleisreleasedfromthecell,whatdoesithavesurroundingit?Bespecific.
Apieceofhostcellmembrane.
9.a.Ahumanbloodcell,whichisthetypeofcellinfectedbyHIV,isabout10micrometers(µm)insize.HIVisabout120
nanometers(nm)insize,or0.12micrometers.Abouthowmanytimessmalleristheviruscomparedtothebloodcell?
It’sabout100timessmaller.
b.Isthedemonstrationanaccuraterepresentationoftherelativesizeofthevirusversushostcell?Explainyouranswer.
No.TheStyrofoamballsarenot100timessmallerthantheplasticbag.
10.Identifyoneimportantdifferencebetweenhowtheviruswasshowntoexitthecellinthedemonstrationandhow
thevirusisactuallyreleasedfromtheinfectedcell.
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Demonstration
Viral Lysis and Budding
Educator Materials
Studentsshouldmentionthatinthedemonstration,theplasticbag(cell)isleftwithholes.Inreality,whenHIVbuds
fromacellitdoesnotcauseholestoform.
11.a.Inthisdemonstration,whatrepresentsthevirusparticles?
Thepiecesofpaperrepresentvirusparticles.
b.Whatrepresentsthehostcell?
Theballoonrepresentsthehostcell.
12.Whathappenstothecellwhenanonenvelopedvirusisreleased?
Thecellisdestroyed.
13.Insummary,whatarethetwostrategiesthatvirusesusetoexitinfectedcells?Writeasentencetodescribeeach
one.
Thetwostrategiesarebuddingandlysis.[addsamplesentencesforthedescriptions?]
AUTHORS
WrittenbyPatriciaNolanBertino,Scotia-GlenvilleHighSchool,andAnthonyBertino,CanandaiguaAcademy.JamesBlankenship,PhD,Cornell
University,advisedontheproject.AdditionalwritingbyMaryColvard.IllustrationsbyHeatherMcDonald,PhD.
EditedbyLeahM.Cataldo,PhD,BuckinghamBrowne&NicholsSchool;KarenGulliver,consultant;andLauraBonetta,PhD,HHMI.Reviewedby
MelissaCsikari,HHMI.
ScientificreviewbyAllenBateman,PhD,DebbyWalser-Kuntz,PhD,CarletonCollege,MunirSyed,PhD,HartwickCollege.
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