Blueprint for life (2 Hours) - Siemens STEM Day

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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:

85121215

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.]