CellDivision

Celldivisionoccursinaseriesofstages,orphases.

Interphase•OccursBEFOREmitosisbegins•DNAiscopiedanddoubles.•DNAappearsasthreadlikecoils(chromatin)atthestart,buteachcopychangestosisterchromatidsandareconnectedbyacentromerebytheendofthisphase.• Interphaseisaperiodofgrowthanddevelopment(cellsspendmostoftheirlivesinthisphase)

centromere

Chromosome

Sisterchromatids

Chromosomes::• Every organism (species) has a

specific and unique number of chromosomes their cells.o Humans: 46 chromosomeso Dog: 78 chromosomeso Goldfish: 94 chromosomeso Lettuce: 18 chromosomes

THISMARKSTHEENDOFINTERPHASE

• Mitosisisaseparatesetofphasesthatoccursafterinterphase.• Celldivisionbeginsafter interphase.• Mitosis isthefirstpartofcelldivision.Inmitosis,thenucleus divides

MITOSIS BEGINS(PMAT)

Prophase(“earlier”/“before”)•Centriolesappearandbegintomovetooppositeendsofcell(poles)•Spindlefibersformbetweenthepoles

centriole

Spindlefibers

Metaphase(middlephase)

• Sisterchromatidsattachtothespindlefibersandlineupinthemiddleofthecell(attheequator).

equator

Anaphase(apart)

•Chromatidsseparateandbegintomovetooppositeendsofthecell

Telophase

•Twonewnucleiform•Chromosomesappearaschromatin(threadsratherthanrods)

MITOSISENDS

Cytokinesis•Divisionofthecytoplasm•Actuallybeginswhiletelophaseisending(phasesoverlap)•Mitosisendswhilecytokinesisisunderway.

Cytokinesis•Thecellmembranemovesinwardtocreatetwodaughtercells,eachwithitsownnucleusandidenticalDNA.• InAnimalcells• “Cleavagefurrow”•Cytoplasmpinchesin.

Cytokinesis• InPlantcells• “CellPlate”• Formsacrossthecell.

THISISTHEENDOFCELLDIVISIONTwonewdaugher cellsbegininterphase

CellCycleSummary:

Note thatmostofthecell’slifeisspentininterphase.

Celldivisionismadeupoftwoparts:mitosis– divisionofthenucleuscytokinesis– divisionofthecytoplasm

CellDivisionControl

•Somecellslosetheirabilitytocontroltheirrateofcelldivision– theDNAofthesecellshasbecomedamagedorchanged(mutated)•Thesesuper-dividingcellsformmassescalledtumors

•Benigntumors:notcancerous – thesecellsdonotspreadtootherpartsofthebody

•Malignanttumors:Cancerous- thesecellsbreaklooseandcaninvadeanddestroyhealthytissueinotherpartsofthebody

APOPTOSIS

• thedeathofcellsthatoccursasanormalandcontrolledpartofanorganism'sgrowthordevelopment.• Notonlydoorganismsneednewcellstobemade,oldcellsalsoneedtobe“retired”orremoved.• Wheneitherthedivisionofcellsortheretiringofcellsdoesnottakeplacenormally,irregularcellgrowthresults• Thesetypesofconditionsleadtocancer.

• Stage0. Thisisusedtodescribecancerinsitu,whichmeans“inplace.”Stage0cancersarestilllocatedintheplacetheystartedandhavenotinvadednearbytissues.Thisstageofcancerishighlycurable,usuallybyremovingthetumorwithsurgery.• StageI. Thisisusuallyasmallcancerortumorthathasnotgrowndeeplyintonearbytissuesandhasnotspreadtothelymphnodesorotherpartsofthebody.Itisoftencalledearly-stagecancer.• StageIIandIII. Thesestagesindicatecancersortumorsthatarelargerinsize,havegrownmoredeeplyintonearbytissue,andhavespreadtolymphnodes,butnottootherpartsofthebody.• StageIV. Thisstagemeansthatthecancerhasspreadtootherorgansorpartsofthebody.Itmayalsobecalledadvancedormetastaticcancer.

Identifyingthestageshelpsto:• determinetreatment

• predicttheriskofrecurrence