biology: cell division and cancer

HS9-12,Biology:CellDivision&Cancer©AmbitiousScienceTeaching2017

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CancerCells [PhotobyDr.CecilFoxviaWikimediaCommons]

Biology:CellDivisionandCancer

HighSchool9-12 CorinMaloneAuburnRiversideHighSchool,AuburnSchoolDistrictMaterialsadaptedfrom“NotAnOldPerson’sDisease”byNationalCenterforCaseStudyTeachinginScience*and“ACaseofSkinCancer”byScienceTake-Out**

* http://sciencecases.lib.buffalo.edu/cs/ ** http://www.sciencetakeout.com/


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Anchoringphenomenon:

Sofia,ayoungfair-skinnedwoman,observedconcerningchangestoamoleonherleg.Sofia’smoledemonstratedthecharacteristicsofmelanomaasdefinedbytheABCDEs1.Herconcernledhertoaskindoctorforfurtherdiagnosisthroughbiopsy.Thebiopsyrevealsthatshedoesinfacthavemelanoma,anaggressiveformofskincancer.

Essentialquestionaboutphenomenon/unit:

● Howdodifferentcellswithintheskinfunctiontoprovideprotectionagainsttheelementslikeultraviolet(UV)light?

● WhateffectdoesUVlighthaveoncellsandDNA?● Whataretheeffectsofmutationsonthefunctioningoftheproteins?

● Whyandhowdocellsdivide?

● Whatismelanomaandwhyisitsodangerous?

Scientificexplanation:Sofia’sskiniscomposedofthreelayers,theepidermis,dermisandhypodermis.Itisthefirstlayer,theepidermis,whichprovidesherbodyprotectionfromtheelements,includingUVlight.Theepidermisismadeoftwotypesofcells,keratinocytesandmelanocytes.Keratinocytesformmostoftheepidermisandtakethebruntoftheenvironmentalexposure;whilemelanocytesproducethepigmentmelaninthatisdistributedtokeratinocytes.Melaninnotonlygivesskinitspigmentation,butmoreimportantlyprotectstheDNAthatlieswithineachcell’snucleusagainstUVdamagebyabsorbingandscatteringtheenergy.ThemoremelaninapersonproducesthemoreUVprotectiontheyhave.Molesareclumpsorclustersofmelanocytesthatappearatthesurfaceoftheskinduringthecourseofagingandmoresunexposure.

Sofia’squestforatanthroughoutherlifeexposedhertomoreandmoreUVlight.WhenexposedtoUVlight,theenergycausedtwonucleotideswithinDNAtosticktogethercausingakinkinthedoublehelix.Mostofthetimethekinkcanbefixedwithcellmachinery,butifthekinkcannotbefixedthecellwilldieduetotheinabilitytoreplicateitsDNA.{WhencellsareexposedtotoomuchUV,morepartsoftheDNAaredamagedandthecelldies.}Onsomeoccasions,thecellmachineryinaccuratelyfixedtheDNAbyreplacingthejoinednucleotideswithdifferentnucleotides,causingamutationorachangeintheDNAsequence.

Whetheramutationisharmful,helpful,orneutraldependsonseveralfactors,butmostimportantlywhetherornotthemutationoccurredinasectionofDNAcalledagene.Genescontaintheinstructionsformakingproteinsthatcarryoutlifefunctions.Whenthesequenceofnucleotidesinthegeneisaltered,thestructureandfunctioningoftheproducedproteinisalteredaswell.

1asymmetrical,bordersuneven,colorsvaried,diameterlarger,evolving


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OneimportantlifefunctionwithinSofia’sskinisthecontinualregenerationofskincells.Inhealthycells,regenerationthroughcelldivisionoccursviaacontrolledprocesscalledthecellcycle,inwhichcellsgothroughphasesofgrowth,DNAreplicationandmitosiswithcheckpointsinbetweeneachphase.Ateachcheckpoint,proteinsproducedbycellcyclegenes(proto-oncogenesandtumorsuppressorgenes)assessifeachphasewassuccessfullycompleted.Innormalfunctioningcells,successfulcheckpointsleadtocontrolledcelldivisionanddifferentiation,whileunsuccessfulones’leadtoaprogrammedcelldeath,alsocalledapoptosis.

UnfortunatelyforSofia,oneormoregenesresponsibleforproducingtheproteinsneededforcheckpointsbecamemutated.Functioningcellcyclegenes(andcellcycleproteins)arenecessaryforthecontrolledcelldivision.Withoutthisability,hermelanocytesbegantodivideuncontrollablyleadingtothechangessheobservedinhermoleandthediagnosisofmelanoma.

TheobservedchangesofSofia’smolewerethesignsofalargerproblemoccurringbeneaththeskin.AfteryearsofUVlightexposure,atleastoneofSofia’smelanocyteswithinhermolehadmutatedcellcyclegenes.Thesemutatedcellcyclegenesdisruptedthefunctionoftheproteinsthattheycodeforandresultedintheuncontrolledcelldivisionofthatmelanocyte.Asthatmelanocytebegantodivideuncontrollably,itproducedtheobservedchangesinthemolebutalsoproducedatumorbeneaththeskin.Continuedgrowthofthetumorcouldleadtomoreseriousformsofmelanoma,inwhichindividualmelanocytesbreakofffromthetumorandspreadthroughthebloodstreamtootherpartsofthebody.Whenacancercellspreadsfromitsoriginaltumortootherpartsofthebodyitcandisruptthefunctioningofotherorgansandpotentiallyleadtodeath.Thebestapproachforreducingone’sriskfordevelopingmelanomaandothertypesofskincanceristoreduceUVlightexposure.

NGSSPerformanceExpectationsaddressedinthisunit:

Standard PE DCI CCC

HS-LS1-2 Developanduseamodeltoillustratethehierarchicalorganizationofinteractingsystemsthatprovidespecificfunctionswithinmulticellularorganisms.

LS1.A:StructureandFunctionMulticellularorganismshaveahierarchicalstructuralorganization,inwhichanyonesystemismadeupofnumerouspartsandisitselfacomponentofthenextlevel.

SystemsandSystemModels

HS-LS1-4 Useamodeltoillustratetheroleofcellulardivision(mitosis)anddifferentiationinproducingandmaintainingcomplexorganisms.

LS1.B.GrowthandDevelopmentofOrganismsInmulticellularorganismsindividualcellsgrowandthendivideviaaprocesscalledmitosis,therebyallowingtheorganismtogrow.Theorganismbegins

SystemsandSystemModels


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asasinglecell(fertilizedegg)thatdividessuccessivelytoproducemanycells,witheachparentcellpassingidenticalgeneticmaterial(twovariantsofeachchromosomepair)tobothdaughtercells.Cellulardivisionanddifferentiationproduceandmaintainacomplexorganism,composedofsystemsoftissuesandorgansthatworktogethertomeettheneedsofthewholeorganism.

MS-LS3-1 Developanduseamodeltodescribewhystructuralchangestogenes(mutations)locatedonchromosomesmayaffectproteinsandmayresultinharmful,beneficial,orneutraleffectstothestructureandfunctionoftheorganism.

LS3.A:InheritanceofTraitsGenesarelocatedinthechromosomesofcells,witheachchromosomepaircontainingtwovariantsofeachofmanydistinctgenes.Eachdistinctgenechieflycontrolstheproductionofspecificproteins,whichinturnaffectsthetraitsoftheindividual.Changes(mutations)togenescanresultinchangestoproteins,whichcanaffectthestructuresandfunctionsoftheorganismandtherebychangetraits.LS3.B:VariationofTraitsVariationsofinheritedtraitsbetweenparentandoffspringarisefromgeneticdifferencesthatresultfromthesubsetofchromosomes(andthereforegenes)inherited.

StructureandFunction

HS-PS4-4 Evaluatethevalidityandreliabilityofclaimsinpublishedmaterialsoftheeffectsthatdifferentfrequenciesofelectromagneticradiationhavewhenabsorbedbymatter.{Specifically,shorterwavelengthelectromagneticradiation(UV,X-rays,gammarays)canionizeatomsandcausedamagetolivingcells.}

PS4.B:ElectromagneticRadiationWhenlightorlongerwavelengthelectromagneticradiationisabsorbedinmatter,itisgenerallyconvertedintothermalenergy(heat).Shorterwavelengthelectromagneticradiation(ultraviolet,X-rays,gammarays)canionizeatomsandcausedamagetolivingcells.

CauseandEffect


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SummaryTableofActivitiesinUnit

Activity LearningTarget EvidenceStudentsCouldGain

ConnectiontoPhenomena

Activity1:Sofia,Melanoma&theABCDE’s(InitialModel)

Developamodeltoexplainyourthinkingaboutthegrowthanddevelopmentofawoman’smoleovertime.

Sofia’smoleshowsallsignsofmelanoma(allABCDEs).

Developinitialmodelsusingpriorknowledgeandbackgroundstory.

Activity2:

HowWeGetOurSkinColor

(Interactiveanimationusingmodelstoexplainthestructureandfunctionoftheskin).

Useamodeloftheskintodescribethestructureandfunctionoftheepidermis.

Thetoplayerofourskinismadeoftwocellsthatworktogethertoprovideprotection.One(keratinocytes)formawaterproofbarrier,theother(melanocytes)makemelanin.

MelaninhelpsprotectourskinfromUVlight.ItlookslikeanumbrellaoverthenucleusandabsorbsUVlight.ThishelpsprotectourDNAfromdamaging.

Amoleisaclusterofthecellsthatmakethepigmentmelanin,andarenotgenerallycancerous.

HS-LS1-2● Thetoplayerofourskin(epidermis)protectsusfromourenvironmentandismadeoftwocelltypes,melanocytesandkeratinocytes.

● Melanocytesmakemelaninandspreadthemelanintothesecondtypeofcell.

● Keratinocytesmakeupmostofthetoplayerofourskin.Thesecellseventuallydietoformawaterproofbarrier.

● MelaninmakesaprotectivecaplikeanumbrellaoverthenucleustoprotecttheDNAfromUVlight.

● Amoleisaclusterofmelanocytes.

Activity3:

SimulatingtheeffectsofUVlightonDNA

ModeltheeffectsofUVlightonDNA.

UVlightcancausechangesinourDNA.IftheDNAcannotbefixedamutationcouldresult.

HS-PS4-4● When exposed to UV light,

the energy caused two nucleotides within DNA to stick together causing a kink in the double helix.

● Most of the time the kink can be fixed with cell machinery, but if the kink cannot be fixed the cell will die due to the inability to replicate its DNA.


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Activity4:

TheEukaryoticCellCycle&CellDivision

Useamodelofthecellcycletoexplainthegrowthanddevelopmentofcellsovertime.

Thecellcycleisasequenceofeventsthatendswithcelldivision.Celldivisionallowslivingthingstogrowandrepairdamage.Checkpointsmakesurecelldivisionisnormal.

HS-LS1-4● Organisms require cell

division for growth and regeneration of dead cells.

● Cell division is a controlled process with phases.

● Between each phase are checkpoints that determine if the cell continues through to the next to ultimately divide.

● In normal cells, successful checkpoints lead to controlled cell division; while unsuccessful ones’ lead to apoptosis (cell death).

Activity5:

Genes,Mutations,andCancer

Criticallyreadscientificinformationtoexplainthecauseandeffectrelationshipbetweenmutationsandcancer.

Mutationshappeneverydayinourbodies.OurcellscanfixmostDNAdamage,sometimesitcan’t.Ifamutationhappensinspecialcellcyclegenes,itcouldleadcancer.Onecancercelldividesuncontrollablyandcantakeoverhealthycellsandmaybespreadtotherestofthebody.

MS-LS3-1● Whether a mutation is

harmful, helpful, or neutral depends on the mutation occurring in a section of DNA called a gene.

● Genes contain the instructions for making proteins. When the sequence of nucleotides in the gene is altered, the structure and functioning of the protein is also altered.

● When one or more genes responsible for producing the proteins needed for checkpoints in the cell cycle become mutated, uncontrolled cell division could result, leading to cancer.

Activity6:

SunSafetyLab

(Groupdesignedlabtocomparesunscreenandsunscreen

DesignandconductaninvestigationtocomparetheeffectivenessofsunscreentoreducingexposuretoUVlight.

DamagingUVlightcanbereducedthroughseveralmethods.

HS-PS4-4● The best approach for

reducing one’s risk for developing melanoma and other types of skin cancer is to reduce UV light exposure.


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alternatives.)

Activity7:

FinalModel/Explanation

Developamodelbasedexplanationtoexplainthegrowthanddevelopmentofawoman’smoleovertime.

TheobservedchangesofSofia’smolewerethesignsofalargerproblemoccurringbeneaththeskin.AfteryearsofUVlightexposure,atleastoneofSofia’smelanocyteswithinhermolehadmutatedcellcyclegenes.Thesemutatedcellcyclegenesdisruptedthefunctionoftheproteinsthattheycodeforandresultedintheuncontrolledcelldivisionofthatmelanocyte.Asthatmelanocytebegantodivideuncontrollably,itproducedtheobservedchangesinthemolebutalsoproducedatumorbeneaththeskin.Continuedgrowthofthetumorcouldleadtomoreseriousformsofmelanoma,inwhichindividualmelanocytesbreakofffromthetumorandspreadthroughthebloodstreamtootherpartsofthebody.Whenacancercellspreadsfromitsoriginaltumortootherpartsofthebodyitcandisruptthefunctioningofotherorgansandpotentiallyleadtodeath.

ModelTemplate


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AdditionalDocuments

InitialModelExample

ModelRevisionExample


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FinalModelExample