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Transcript of SCRIPT V3
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SCRIPT
Version3
Thehumancell.
Thereareover30trillioncellsinthehumanbody.Eachoneofthesecellslineup
wantingandwaitingtodivide.Thesecellsallwanttodividesothattheycanhelp
thehumanbodygrowandrepairitsself.
Tobealoudtodivideacellmustgothroughcertainstagesofcheckpointsand
developments.ThisiscalledInterphase,orotherwiseknownasthecellcycle.
Interphasecanbesplitinto4phase,G1phase,Sphase,G2phaseandMphase,
eachwithitsowncheckpoint.
ThisstageofwaitingtobealoudtodivideoncemoreiscalledG0phase.This
stageistherestingplaceofallcellsbeforetheyaloudbackontothecellcycle.
Some,moredamagedoroldercellswillneverbealoudontothecellcycle.
IfthecellisdeemedhealthyitisaloudtopassthroughthegateontotheG1
phaseofthecycle.
Inthisphasethecellphysicallygrows,preparingforcelldivision.
Whenthecellreachesthecheckpoint,itischeckedforanyerrors.Ifanerrorisfound,thecellisremovedfromthecellcycleandissentbacktotheG0phase.
Thischeckpointisoneofthehardestforacelltopassthrough.Acellcanbe
removedatanyofthecheckpointsifanerrorisfound.
Ifnoerrorsarefound,thecellcanmoveontothenextphase,theSphase.
Inthisphase,theDNAinthecellisduplicated.
Againitischeckforanyerrors.Itisthenaloudtopassontothenextphase.
Thisphase,theG2phaseisthelastphaseofthecycleforthecelltogrowand
develop,readyfordivision.
Ifitremainshealthyandisreadyfordivisionitentersthelastphaseofthecycle.
ThecellthenisaloudtodivideintotwobyMitosisorMphase.
Mphasecanagainbesplitintoseveralsmallerphases.
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ThesephasesarecalledProphase;Prometaphase;Metaphase;Anaphase;
TelophaseandCytokinesis.
Eachofthesestagesarekeyforahealthydivision.
TheCellhastwocopiesofitsDNA,allspreadoutinlongstringsthankstotheSphase.
Beforethecellbeginstodivide,theDNAformsXshapedchromosomes.Eacharm
ofthechromosomeisanexactduplicateoftheother.
TheChromosomesthenlineupatthecentreofthecellandcellspindlefibers
pullthemapart.Thetwoarmsofeachchromosomegotooppositeendsofthe
cell.
Membranes formaround eachof the sets ofchromosomes. Thesebecome thenucleiofthetwonewdaughtercells.
Lastlythecytoplasmdividesbythemeanofacontractileringthatcleavesthe
cellintotwodaughtercells
NowtherearetwocellscontainingexactlythesameDNA.
ThesetwonewdaughtercellsgototheendofthecueinG0phase,waitingto
divide.
Thishighwayofcellsisconstantlyhelpingthehumanbodygrowandrepair.
Thisisthelifeofacell.
