Cell cycle

cell cycle

1. Cell Cycle
Dr. PratibhaBisen
Dept. Plant Breeding & Genetics
College of Agriculture, Balaghat
JNKVV Jabalpur (M.P.)

2. Cellcycle,theorderedsequence
ofeventsthatoccurinacellin
preparationforcelldivision.
Scientisthaveidentifieda
repeatingcycleofeventsinthelife
ofcell.
Insimplerwords,Cellcyclecan
bedefinedasasequenceofevents
takingplaceforthedevelopment
andgrowthofthecelltakingplace
intravenouslyinacellleadingtothe
formationoftwodaughtercells
throughDNAduplicationand
cytokinesisalongwiththedivision
ofcellorganelles.
Introduction

3. Cell cycle
Phases of Cell cycle

4. Cell cycle
Interphase
Phases of Cell cycle

5. Cell cycle
Interphase Mitosis
Phases of Cell cycle

7. G1
Sub Phases of Interphase

8. G1
S
Sub Phases of Interphase

9. Sub Phases of Interphase
G1
S
G2

10. G1
Thisistheprimarystageoftheinterphase,knownastheG1orfirstgap
phase.
Thisphaseischaracterizedbychangesinthechromosomesfromthe
condensedtotheextendedstateinadditiontoarangeofmetabolic
activitiesleadingtotheinitiationofreplicationofDNA.
Characteristicsofthechromatinfibresinthisphaseare–lesscoiledand
slender,extendedfullyandreadyfortranscription.
TheprocessoftranscriptionresultsintheproductionofRNAsandalso
asequenceofproteinmoleculesvitalforDNAreplicationtobeinitiated
G1phaseislengthierthantheotherthreephasesandvariesfromcellto
cell
DNAsynthesisinthisphaseisinitiatedatadistinctcheckpoint.Thecell
progressestowardsdivisiononceallthebiochemicaleventsatthis
particularpointhaveconcluded.

11. S
ItisanactiveDNAsynthesisandhistonesynthesisphaseoftheinterphase
Herethechromosomenumberduplicatesenabledbylinkedproteinsand
DNAreplication.Mostofthehistoneproteinsynthesisoccursinthisphase
thoughsomeofitoccursinG1phase
IdenticalpairofDNAmoleculesareformedastheprocessofDNA
replicationisdiscontinuousandsemi-conservative
Evenafterthechromosomeshavedoubled,thesisterchromatidsare
securelyattachedtothecentromericregion

12. G2
ThisphaseissucceededbytheSphase.Herethechromosomescompriseof
twochromatidsthuscellhasdoublethequantityofDNA.
Here,thecellrestoresitsenergy,producingproteinsessentialfor
chromosomestomanipulate
Fewofthecellorganellesarereplicated.Cytoskeletondismantlestorender
resourcesformitosis
Additionalgrowthofcellmaybeobserved.Beforethecellentersthefirst
phaseofmitosis,theconcludingpreparationsofthemitoticphasemustbe
done.

13. G2

15. The G0 phase or
restingphaseisaperiodin
thecellcycleinwhichcellsexist
inaquiescentstate.
G0phaseisviewedaseitheran
extendedG1phase,where
thecellisneitherdividingnor
preparingtodivide,oradistinct
quiescentstagethatoccursoutside
ofthecellcycle.
G0

16. M
ThisphaseissucceededbytheG2phase.Herethecelldividesintotwo
daughtercellsalongwithequaldistributionofchromosomesbetweenthe
daughtercells.OncetheMphasestepsintotheG1phase,thenextcellcycle
isinitiatedtoberepeated.
Duringthemitotic(M)phase,thecelldividesitscopiedDNAand
cytoplasmtomaketwonewcells.
Mphaseinvolvestwodistinctdivision-relatedprocesses:mitosisand
cytokinesis.

19. Theprogressionofcellsthroughthecellcycleiscontrolledbycheckpoints
atdifferentstages.
ThesedetectifacellcontainsdamagedDNAandensurethosecellsdonot
replicate.
TheRestrictionpoint(R)islocatedatG1andisakeycheckpoint.The
vastmajorityofcellsthatpassthroughtheRpointwillendupcompletingthe
entirecellcycle.OthercheckpointsarelocatedatthetransitionsbetweenG1
andS,andG2andM.
IfdamagedDNAisdetectedatanycheckpoint,activationofthecheckpoint
resultsinincreasedproteinp53production.p53isatumoursuppressorgene
thatstopstheprogressionofthecellcycleandstartsrepairmechanismsfor
thedamagedDNA.IfthisDNAcannotberepaired,thenitensuresthecell
undergoesapoptosisandcannolongerreplicate.
Thiscellcycleisalsocloselyregulatedbycyclinswhichcontrolcell
progressionbyactivatingcyclin-dependentkinase(CDK)enzymes.
Regulation