www.siemensstemday.com 1 Topic: DNA as the blueprint for a living cell Real World Science Topics: • An exploration to discover how biological information is stored • An exploration of DNA, the molecule used to store biological information Objective Students will learn that DNA encodes the information necessary for specifying biological traits. Materials Needed for Demonstration: chalkboard or overheard projector Materials Needed for Each Student: blank paper colored markers or pencils 1 T raw wheat germ 1 t dish detergent 4 T rubbing alcohol bowl of ice 4 T warm water (50–60° C) 2 clear plastic beverage cups permanent marker or masking tape and a pen (for labeling the cups) coffee stirrers bent paper clip (see illustration) measuring spoons (teaspoon and tablespoon) BLUEPRINT FOR LIFE (2 Hours) multicolored chalk or pens Addresses NGSS Level of Difficulty: 3 Grade Range: 6-8 OVERVIEW In this activity, students will explore DNA as a code for biological traits and extract samples of DNA from the interior of living cells.
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Topic: DNA as the blueprint for a living cell
Real World Science Topics:• Anexplorationtodiscoverhowbiologicalinformationisstored
• AnexplorationofDNA,themoleculeusedtostorebiologicalinformation
ObjectiveStudentswilllearnthatDNAencodestheinformationnecessaryforspecifyingbiologicaltraits.
Materials Needed for Demonstration:
chalkboardoroverheardprojector
Materials Needed for Each Student:blankpaper
coloredmarkersorpencils
1Trawwheatgerm
1tdishdetergent
4Trubbingalcohol
bowlofice
4Twarmwater(50–60°C)
2clearplasticbeveragecups
permanentmarkerormaskingtapeandapen(forlabelingthecups)
coffeestirrers
bentpaperclip(seeillustration)
measuringspoons(teaspoonandtablespoon)
Blueprint for life (2Hours)
multicoloredchalkorpens
Addresses NGSS Level of Difficulty: 3 Grade Range: 6-8
OVERVIEW
In this activity, students will explore DNA as a code for biological traits and extract samples of DNA from the interior of living cells.
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Note:rawwheatgermisavailableatnaturalfoodstores(suchasWholeFoodsorTraderJoe’s).Itmayalsobeavailableinthenaturalfoodsectionofalocalgrocerystore.Ifrawwheatgermisnotavailable,thisexperimentmaybedonewithpeas,frozenspinach,fruit,oronions.Athermoswithapumpprovidesaneffectivewaytomakewarmwateravailabletostudents.Anicebucketcontainingabottleofrubbingalcoholprovidesaneffectivewaytomakeice-coldalcoholavailabletostudents.Adultsupervisionwillberequiredtoassiststudentswithobtainingtheirwarmwaterandalcoholsamples.
Teacher PreparationPreparematerialsforthelabactivityaheadoftime.Setupacentralstationfordistributingthewarmwaterandice-coldrubbingalcoholduringthelabactivity.
Forthewarm-upactivity,groupsoftwotofourstudentswillneedtoworktogetheratatablewhereeachstudentcanwriteonhisorherownhandoutsheet.
Forthelabactivity,studentsshouldworkindividuallytoextractasampleofDNAfromwheatgerm.Thesametablesetupusedearlierwillworkwellforthissecondactivityalso.
Blueprint for life
Science and Engineering Practices
NGSS Three-Dimensions
Developing and Using Models
• Develop and use a modelto describe phenomena.
DisciplinaryCore Ideas
Crosscutting Concepts
• Complex andmicroscopic structuresand systems can bevisualized, modeled, andused to describe howtheir function dependson the shapes,composition, andrelationships among itsparts, therefore complexnatural structures/systems can be analyzedto determine how theyfunction.
• Genes are located in thechromosomes of cells, wtiheach chromosome paircontaining two variants ofeach of many distinct genes.Each distinct gene chieflycontrols the production ofspecific proteins, which in turnaffects the traits of theindividual.
• Changes (mutations) togenes can result in changes toproteins, which can affect thestructures and functions ofthe organism and therebychange traits.
Structure and Function
LS3.A: Inheritance and Traits
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1. Warm-up Activity:Writethefollowingontheboard:
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Tellstudentsthatitisagreetingandaskthemiftheycanfigureoutwhatitsays.Leadstudentstorecognizethatyouhavewrittentheword“hello”incode.Eachletterisrepresentedasanumber,witha=1,b=2,c=3,andsoon.
Askstudentsiftheyknowthatthecellsintheirbodiescontainmoleculesthatcodeforinformation.Provideafewexamplesofthetypeofinformationencodedbythesemoleculesinahuman:blueeyecolororcurlyhair,forexample.Askforvolunteerstosuggestwhatmoleculemightcontainthisinformation.LeadstudentstosuggestDNAastheinformation-carryingmoleculeinacell.
Drawacircleontheboardtorepresentacell.Drawanothercirclewithinthefirsttorepresentthecellnucleus.Insidethenucleus,drawasimplesketchofDNAastwostraightstrandswithconnecting“rungs”likealadder.ExplainthattheDNArepresentsacodeformoleculescalledproteins,muchliketheseriesofnumbers
representsacodeforthewordhello.DrawanarrowfromtheDNAtothecytoplasmportionofthecell(outsidethenucleus)andwritethewordproteinsattheendofthearrow.ExplainthatthesequencewithintheDNAislikeacodethattellsthecellthespecificproteinstomakeinthecytoplasm.DifferentDNAsequencesmakedifferentproteins.
TellstudentsthattheyaregoingtodecodetheDNAofsomeplantseedstopredictwhattheplantswilllooklikeaftertheyhavegrown.Explainthattheactivityisonlyasimulationtoshowhowacodecanwork.DNAusesacodethatisdifferentthanthecodestudentswilluseinthesimulation.
2. DistributetheBlueprint for Lifehandoutandmaterialstoeachgroupoftwotofourstudents.
3. StudentsshouldfirstdecidehowtheywilldecodetheirDNA.TheyaregivenaclueinthestrandofDNA
ontheirhandout:thewordstartisassociatedwiththefirstfivelettersinthesequenceandthewordstopis
associatedwiththelastfourletters.Donottellstudentsthis;onlyprovidethemwiththehintthattheyhavealloftheinformationnecessarytodecodetheirDNAsequence.Circulateamonggroupstoassistifnecessary,butallowteamsenoughtimetodiscussandsolvetheproblemthemselves.
4.onceeachteamhasfiguredoutthekeytothecode,havetheteammembersdivideuptheirDNA
sequencesothateachstudenttranslatesthecodedsequenceofoneportion.Teamsshouldworktogether
tocollectallthedecodedsequencesintoonecompletedecodedsequence.
5. Thetranslatedsequencewillprovidetheteamtheinformationnecessarytoidentifythetraitstheirplantwillhavewhenitgrowstoadulthood.Havetheteamcreateapictureoftheirplantandgiveitaninventivenameoftheirchoice.
6. Lab activity:HavestudentsextractDNAfromfreshwheatgermoranotherplantsource.TellstudentsthatDNAispresentinalllivingcells,soasimilarprocedurecouldbeusedtoextractDNAfromtheircells.
7. Beforestudentsgetstartedontheextraction,gobacktothedrawingofthecellontheboard.AskstudentswhatwillhavetohappentoremoveDNAfromacell.Leadstudentstounderstandthatcellswillhavetobe
STEPS fOR Blueprint for life
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brokenopeninordertoallowtheDNAtoberemoved.Inanimals,cellsaresurroundedbyacellmembrane;plantcellshavebothacellmembraneandacellwall.
8. Explaintostudentsthatdetergentwillhelpdisruptthecellmembranesandcellwallsoftheplantcellstheywillbeworkingwith.Whentheyadddetergenttothewheatgermmixture,thedetergentmoleculesmixwiththecellwallandcellmembranemolecules,causingthemtomoveawayfromoneanother.
9.oncetheDNAisreleasedintothedetergentsolution,itmustbeisolatedfromtheothercellmaterial.DNAtendstoclumptogetherandcomeoutofsolutionifalcoholisadded.Studentswillcarefullyaddice-coldalcoholasalayerontopoftheirwheatgermmixtureasawaytodothis.Itisimportantthattheydothiscarefullysothatthewaterandalcoholdonotmixtoomuch.ItisatthisstagethatstudentscanactuallyseeevidenceoftheDNA—itturnsthealcohollayermilkywhite.Ifthealcoholandwateraremixedtogether,noDNAprecipitatewillbeformedandthestudentswillnotbeabletoseetheDNA.Itisadvisabletodemonstratethissteptohelpguidestudentstoavoidthispotentialproblem.
10. Havestudentsbeginbygettingtwoplasticcups,labelingthem”1”and”2,”andpreparingthemasfollows:
a. Leavecup1alonefornow.Later,studentswillplaceice-coldrubbingalcoholinit.
b. Tocup2,add1Trawwheatgermand4Thotwater(50–60°C).Mixthesetogetherwithacoffeestirrer.
11. Tocup2,add1teaspoon(t)ofdishdetergent.Mixverygentlyeveryminuteforfiveminutes.Cautionstudentsnottomixthesolutiontoovigorously;iftheymixittoohard,theDNAwillbreakintomanysmallfragments,andthefinalstepwillnotworkproperly.
12. Tocup1,add4tablespoons(T)ofice-coldrubbingalcohol.Tipcup2atanangleofabout45°andveryslowlypourthechilledalcoholfromcup1downthesideofcup2sothatitformsalayerontopofthewheatgerm/detergentmixture.Donotallowthetwoliquidstomix.Slowlyreturnthecuptoanuprightpositionandplaceitonthedeskortableforafewminutes.observeanysignsofDNAprecipitation(formationofamilkywhitesubstance)wherethetwoliquidsmeet.
13. Afterafewminutes,studentsshouldobserveamilkywhiteswirlofDNAinthealcohollayer.Dipthebentpaperclipintothealcoholandcarefullypullthewhiteprecipitateoutofthecup.ThisthickblobcontainsmostlyDNA,alongwithsomeproteinsandothercellularmaterial.
14. ExplaintostudentsthatthisextractionprocedureissimilartotheprocedureusedbyaforensicscientistwhenheorsheisolatesDNAfromhumancells.However,theforensicscientistmustperformseveralmorestepstoremoveallproteinsandothercelldebrisbeforesequencingtheDNA.
Blueprint for life Extension ActivityStudentsoneachteamcancreatetheirowncodeanddevelopblueprintsforalienlifeforms.Teamscan
challengeoneanothertodecodetheircreations.Encouragestudentstobecreativeintheircodes—forexample,theymightuseshapesorcolorsinsteadofnumbersorletters.Eachteamshouldfirstcreateakeyforitscode,toensurethatthetranslationisaccurate.
STEPS fOR Blueprint for life
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What is DNA? DNAisanenormousmoleculemadeupofaseriesofindividualunitscallednucleotides.Eachnucleotidecontainsaportioncalledabase.Therearefourpossiblebases:cytosine,guanine,adenine,andthymine.ItisthespecificsequenceofthesebasesalongastrandofDNAthatprovidestheinformationnecessaryforthecelltoconstructtheproteinsitneedsforitsvariousfunctions.
DNAisdouble-stranded,meaningthatitiscomposedoftwostrandsofnucleotides.Thetwostrandsarecomplementarybecauseeverycytosineispairedupwithaguanineandeveryadenineispairedupwithathymineinthefinaldouble-strandedDNAmolecule.Thetwostrandstwistintoahelixstructure,asshownbelow:
DNA contains two complemetary strands:
Strand1:<-G-C-T-A-C-G-A-A-T-G-C->
Strand2:<-C-G-A-T-G-C-T-T-A-C-G->
ItmaybeeasiertovisualizeDNAasaladderwiththebasepairslinedupalongtherungsoftheladder.Ifyouthenholdontothetopandbottomoftheladderandtwist,yougetadouble-strandedhelixthatresemblesDNA.
How large is a DNA molecule? Inahuman,DNAisdistributedamong23pairsofchromosomes.EachchromosomecontainsonestrandofDNA.Normally,thesestrandsofDNAaretightlycoiledintocompactstructuresheldinplacebyproteinsthatbindandstabilizethem.However,ifall46piecesofhumanDNAwereuncoiledandlaidendtoend,theresultingmoleculewouldbeabout2meterslong.
Blueprint for life BACkgROuND INfORMATION
PairedBases PolynucleotideBackbone
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Do humans have more DNA than other organisms? No.Therearealittlemorethan3billionpairsofnucleotidesintheDNAinasinglehumanbodycell,butmanyanimalsandplantshavesignificantlymorethanthat.Scientistsarestilltryingtodeterminewhythisis.onethingisknown:NotallDNAcodesforproteins,sothetotalamountofDNAisnotanindicationofthenumbersofproteinsthatanorganismcanproduce.DNAismuchmorecomplicated,withsomesectionsregulatingtheexpressionofotherportions.
Do we know the full sequence of human DNA? Yes.ThetotalsequenceofarepresentativehumanDNAsample—thehumangenome—wascompletedinMay2006.However,withtheexceptionofidenticaltwins,eachperson’sspecificDNAsequenceisunique.The“humangenome”isconsideredarepresentativeexampleofacompletehumanDNAsequence,butthetinydifferencesinthatsequencemakeeachpersonunique.
Blueprint for life BACkgROuND INfORMATION
key VocabularyDNA: deoxyribonucleicacid;themoleculethatencodesbiologicalinformationnecessaryforthecelltocarryoutlifefunctionsextraction: achemicalprocessusedtoseparatesubstancesinamixturetrait: aphysicalcharacteristic,suchashaircolornucleus: theportionofananimalorplantcellwhereDNAislocated cytoplasm: theportionofacellsurroundingthenucleus cell membrane: thestructurethatenclosesacellandcreatesabarrierbetweenthecellinteriorandthesurroundingenvironment cell wall: thestructurethatenclosesaplantcell;plantcellsalsohaveacellmembraneinsidethecellwallgene: thesequenceofDNAthatcodesforoneprotein chromosome: atightlypackedstrandofDNAheldinitspackedformbyproteinsprotein: alargemoleculemadeupofalinearstrandofunitscalledaminoacidsandcoiledinaseriesoftwistsandturnstocreateasphericalshapenucleotide: asmallmoleculethatcanbebondedtootherslikeittoformalongstrandofDNA base: theportionofaDNAmoleculeusedforencodingbiologicalinformation;eachbaseactsinafashionthatisanalogoustolettersinanalphabet
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STuDENT HANDOuT fOR
Blueprint for life
ThesequencebelowrepresentsastrandofDNAthatcodesforspecifictraitsinaplantseed.Asateam,worktogethertodeterminethekeytothecodeusingonlytheinformationprovided.
S t a r t
HGZIGYILZWoVZuHGLKHGZIGGZooHGLKIVWuoLDVIHHGLKHGZIGGSLIMBHGL
KHGZIGHDVVGHXVMGHGLKHGZIGGIZMTFoZIoVZuHSZKVHGLK
S t o p
onceyourteamhasdeterminedthekeytothecode,dividethesequenceintoportionsandalloweachteammembertodecodehis/herportion.Assembleallofthedecodedsequencestodeterminethespecifictraitsthatwillbeproducedinyourplant.
usetheinformationtodrawapictureofanadultversionofyourplant.Chooseaninventivename
foryourplant.
1. Howdidyoudeterminethekeytothecode?
2. DidtheDNAsequencecontaininformationotherthantraitdescriptions?Ifso,whatotherinformationwaspresent?
3. WhyisitimportantforaseedtohaveinformationencodedinitsDNA?
4. IfallplantscontainDNA,whydodifferenttypesofplants(suchaspinetreesandorchids)looksodifferentfromoneanother?
5. DoyouthinkthatyourDNAismoresimilartoyourfriend’sDNAortotheDNAofoneofyourparents?Why?
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TEACHER HANDOUT FOR
Blueprint for life
ThesequencebelowrepresentsastrandofDNAthatcodesforspecifictraitsinaplantseed.Asateam,worktogethertodeterminethekeytothecodeusingonlytheinformationprovided.
S t a r t
HGZIGYILZWoVZuHGLKHGZIGGZooHGLKIVWuoLDVIHHGLKHGZIGGSLIMBHGL
KHGZIGHDVVGHXVMGHGLKHGZIGGIZMTFoZIoVZuHSZKVHGLK
S t o p
[STArTBroADLEAFSToPSTArTTALLSToPSTArTrEDFLoWErSSToPSTArT
THorNYSToPSTArTSWEETSCENTSToPSTArTTrIANGuLArLEAFSHAPESToP]
[Note:thekeyisareversealphabet.Z=A,Y=B,X=C,andsoon.]
onceyourteamhasdeterminedthekeytothecode,dividethesequenceintoportionsandalloweachteammembertodecodehis/herportion.Assembleallofthedecodedsequencestodeterminethespecifictraitsthatwillbeproducedinyourplant.
usetheinformationtodrawapictureofanadultversionofyourplant.Chooseaninventivename
foryourplant.[Studentsshoulddrawpicturesofwhattheythinktheplantmightlooklike.]
1. Howdidyoudeterminethekeytothecode?
[Weusedthestartandstopsequencestofigureoutthatthecodewasthealphabetruninreverse.Z=A,Y=B,X=C,andsoon.]
2. DidtheDNAsequencecontaininformationotherthantraitdescriptions?Ifso,whatotherinformationwaspresent?
[Yes.Thesequencealsocontainedstartandstopsignalsinbetweenthetraitdescriptions.]
3. WhyisitimportantforaseedtohaveinformationencodedinitsDNA?
[Theseedneedstoknowwhatproteinstomakeasitgrows.Itwillacquireitstraitsasitgrows.]
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TEACHER HANDOUT FOR
Blueprint for life
4. IfallplantscontainDNA,whydodifferenttypesofplants(suchaspinetreesandorchids)looksodifferentfromoneanother?
[Plants differintheirDNAsequences.Thosesequencesdeterminetheproteinsthateachplantmakesandthesedifferencesresultindifferenttraitsthatwesee.]
5. DoyouthinkthatyourDNAismoresimilartoyourfriend’sDNAortotheDNAofoneofyourparents?Why?
[MyDNAwouldbemoresimilartomyparent’sDNAbecausemycellscamefrommyparents.]
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