CELL CYCLE CONTROL

Ineukaryotes,heritableinformationispassedtothenextgenerationviaprocessesthatincludethecellcycleandmitosisormeiosisplusfertilization.

ControlofCellDivisionMitosisisunderstrictcellularcontrol.Cellsmustpassthroughaseriesof“checkpoints”tobeallowedtodivide.Ifinternalconditionsarenotappropriate,celldivisionwillnormallybeprevented.

Cancer:Uncontrolledcelldivision.

G1 Checkpoint

• DeterminesifacellshouldreplicateitsDNA• FromherecellseitherenterSphaseorG0• Senescence– Cellsthathavestoppeddividing

Internal control of divisionCellscontrolcelldivisionbycontrollingthepresenceorabsenceofproteinsthatallowforcelldivision.

Ex.MitosisPromotingFactor

Ex.p53

MPF:MitosisPromotionFactor• Cdk:Cyclin-dependentkinase

• Presentinaconstantamount• Cyclin:TheCdk “onswitch”

• Madeinanincreasingamountasthecellmovesthroughinterphase

• MPF:Cyclin+Cdk• Turnsonotherproteinsneededformitosis(e.g.microtubuleformation)

NoCyclin=NoMitosis(WhatTypeofFeedback?)

ExternalControlsProteinsandotherenvironmentalsignalsgeneratedbyothercells

• Progressionthroughthecellcyclecanbetriggeredbyexternalsignals.

• PDGF:PlateletDerivedGrowthFactor• Whatareplatelets?Whydotheymakegrowthfactor

• PositionalInhibition• Normalanimalcellsmustbeanchoredandnottoocrowded(“density-dependent”)

ExternalControlofDivision