cell division - Mitosis in plants final.ppt

mitosis is used for almost all of your body’s cell division needs. It adds new cells during development and replaces old and worn-out cells throughout your life. The goal of mitosis is to produce daughter cells that are genetically identical to their mothers, with not a single chromosome more or less.

1. Cell division

2. Principles of Cell Theory
•All living things are made of cells
•Smallest living unit of structureand functionof all
organisms is the cell
•All cells arise from preexisting cells
The process by which new cells originate
from living cells is called as cell division

3. •The countless divisions of single celled zygote produce an
organism of amazing cellular complexity & organism
•Life is a continuum from one generation to next & there
must be a continued renewal or return to an original state
for the process to occur again
•The cell division continues throughout the life
–25 million cells under go divisions /sec in human
–RBC’s replaced at 100m /min

4. Functions of cell division
1.Growth & development of somatic tissues or organs
2.Regeneration of damaged tissues
3.Production of new organs & tissues
4.Replacement of old organs & tissues
5.Helps in asexual & sexual reproduction
6.Keeping the size of cells within limited range
7. Pre-requisite for the continuity of life & evolution of
various life forms

5. •Thecellthatundergoesdivisionistermedasmother
cellorparentalcell
•Thedescendantsofmothercellcalledasdaughter
cells
•Cellular reproduction
Mother--> Daughter / Mother-->
Daughter
•The stages through which a cell passes from
one cell division to the next form the cell cycle

6. •Thecellcycleisanorderedseriesofmacro
molecularevents
•Duplicationofparentalchromosomesoccurs
duringthe‘Synthesis’phaseofthecelldivision&
oneoftheresultingsisterchromosome
distributedtoeachdaughtercells
•Theprogressionofeukaryoticcellsthroughtheir
cycleistightlycontrolledbydifferenttypesof
proteins,withhighaccuracy(Fidelity)
•Deregulation of cell division may leads to
cancer

7. Cell division includes two events
•Nuclear division (Karyokinesis)
•Cytoplasmic division (Cytokinesis)
As a rule the cytokinesis follows karyokinesis

8. •DJTaylor&team:
reportedthatcellcycleincludes3stages
•Interphase(IPhase)–Synthesis&growthperiod
•MPhase–Processofnucleardivision
•Cytokinesis-Processofdivisionofcytoplasm
•Howard&Pelc:dividedcellcycleinto4phases--G
1,G
2,
S&MPhase
•TheG
1,G
2,Sphasearecombinedtoformtheclassical
interphase

9. G
1phase
•1
st
gapphase–NoDNAsynthesistakeplace
•1
st
growthphase–ItinvolvessynthesisofRNA,
Proteins&membranes
•Itstimeofresumptionofnormalcellmetabolism
whichhasslowedduringpreviouscelldivision
•G
1involvestranscriptionofrRNA,tRNA&mRNA
•DifferentProteinssynthesizedare
•Regulatory proteins which controls various events
•Enzymes (DNA polymerase, other polymerases)
•Tubulin & other mitotic apparatus proteins

10. •G
1phase occupies 30-50% of total time of cell cycle
•Its absent in rapidly dividing cells (Blastomeresof
early embryo of frog & Mammals)
•G
0phase:Terminally differentiated somatic cells
that are no longer divide further
•Arrested at G
1phase
ex: Erythrocytes, Neurons, Striated muscle
cells
G0phaseisviewedaseitheranextendedG1phase,
wherethecellisneitherdividingnorpreparingtodivide,
oradistinctquiescentstagethatoccursoutsideofthe
cellcycle.

11. S phase (Synthesis phase)
•Genome of organism replicated
•Synthesis of DNA & Histone proteins occurs
•At the end of S phase, each chromosome has two
DNA molecules & duplicate set of genes
•It occupies around 35-45%cell cycle

12. G
2Phase
•Pre-mitoticgapphase,secondgapphaseor
secondgrowthphase
•SynthesisofRNAs&Proteinscontinues
•Mitochondria&chloroplastsdivide&spindle
beginstoform

13. Duration of different phases of cell
division (hours)
Organism G1 S G2 Mitosis
Viciafaba12 6 12 1
Mouse 12 6-8 3-4 1
Man 12 10 3 1
Usually, cells will take between 5 and 6 hours to complete S phase.
G2 is shorter, lasting only 3 to 4 hours in most cells.
In sum, then, interphase generally takes between 18 and 20 hours.
Mitosis, during which the cell makes preparations for and completes cell
division only takes about 2 hours.

16. Cell cycle in different types of cells
1.Highly differentiated cells & has lost ability to divide
Ex: Nerve cells, RBCs, Muscle cells
2.Cells that normally do not divide but can induced to
begin DNA synthesis & divide
Ex: Liver cells, Lymphocytes
3.Cells normally passes a relatively high levels of mitotic
activity
ex: Stem cells, apical meristem cells

17. Types of Cell division
Mitosis
Meiosis

18. Mitosis

19. •Greekword-Mitos=Thread
•1
st
usedbyWalterFlemingin1879
•Mitosisisaprocessofnucleardivisioninwhich
replicatedDNAmoleculesofeachchromosomes
arepartitionedintotwonuclei
•Mitosiscantakeplaceineitherhaploidordiploid
cells
ex:Haploids–Fungi,Plantgametophytes,
Drones

20. •The two daughter cells resulting from mitosis possess
a genetic content identical to each other & to the
mother cellfrom which they arose –homotypic or
Equational division
•Mitosis maintains the chromosome numberand
generates new cells for growth & maintenance of an
organism

21. Significance of Mitosis
1.Productionoflargenumberofidenticalcellstoenable
growth&developmentoforganism
2.Regenerationofdamagedtissues&organs
3.Regular&continuousreplacementofoldtissues–
Bloodcells
4.Productionofneworgans-(root/shoot)
5.Productionofidenticalplantprogeniesthrough
asexualreproduction
6.Productionofgametesinplants

22. Mitosis generally divided into 5 stages
1. Interphase
2. Prophase
3. Metaphase
4. Anaphase
5. Telophase
& Cytokinesis
•Cell division is continuous process & gradually
progress from one stage to another

23. Interphase
Telophase-->Interphase-->Prophase
•Chromosomeisfullyextended&uncoiled
•Nucleisurroundedbynuclearenvelope
•Itsnotarestingphase;DNA,RNA,protein
synthesistakeplace
•DNAreplicationprovidesbasisforclassificationof
Interphaseintofollowing3stagesviz.,
•G
1phase,Sphase&G
2phase

24. G1 Phase
•Beginning of Interphase --> G
1--> DNA
synthesis stage
•Synthesis of Proteins & ribosomes for DNA
synthesis & entry of cells into Mitosis

25. ‘S’ Phase
•DNA synthesis take place; as a result of which
chromosome replicate
•DNAsynthesisleadstoproductionofsister
chromatidsfromsinglechromatidsofeach
chromosome
•DNA / Nucleus
•Anaphase, Telophase & G1 -2C
•G2, Prophase, Metaphase -4C
•RNA & protein synthesis are very low

26. G2 Phase
•RNA & proteins synthesis
-Proteins essential for entry of cells to Mitosis
•Components of microtubule synthesis

27. Prophase
•Theappearanceofdefinitethreadlikestructuresinnuclei
(chromosomeappearaslooseballofthinwool)
•Chromosomebecomeshorter&thickerduetocondensation
•Bymidprophase,2chromatidsofeachchromosomebecome
visible
•Nucleolus&nuclearmembrane
remainpresent
•Byend,allchromosome
considerablyshorter&thicker
•Spindleapparatusisnotyet
formed

28. Metaphase
•Nucleolus disappear
•Breakdownofnuclearenvelope&distributionofits
componentsintotheER
•Appearanceofspindleapparatus
Arrangement of chromosomes on
equatorial plate
Centromeres of all chromosomes
arranged on equatorial plate & arms
extended outside this plate

29. Anaphase
•Centromeresofchromosomesdividelongitudinallysothat
sisterchromatidsseparatesfromeachother
•Separatedsisterchromatidsmigratestowardsoppositepoles
Centromereis1
st
portionof
chromosomebegintomove
towardsoppositepole
Chromosome become more
condensed–theyappear
relativelysmallerinsize

30. Telophase
•Itbeginswhenallthechromosomesofcellreachthe
oppositepoles
•Thechromosomesuncoil&becomelong&thin–appear
asalooseballoffinethread
•Newnucleolus,nuclearmembranes&Nuclearenvelope
reorganizedaround2groupsofchromosomes
•Decondensationofchromosome&restorationofinternal
organellesarecharacteristicsofTelophase

32. Cytokinesis
•When mitosis is complete the two daughter cells
are separated by the formation of membrane
between them
•This physical separation of daughter cells is called
as cytokinesis

33. In Animals, cytoplasm division begins with
simultaneous furrowing / invagination on all sides
of plasmalemma in the region of equatorial plate

34. Inplants,separationofcytoplasmbeginsinthe
Centreofthecell&graduallyextendsoutwardson
eachsideinperpendiculartospindleaxis
In plants a wall is laid down between daughter cells
-ER, Golgi products give rise to cell plate &
middle lamella

37. •The daughter cells are genetically identical & has
a complete set of chromosome
•The genetic material is transmitted fully &
faithfully to daughter cells

40. Prophase >Metaphase >Telophase >Anaphase