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1. 1

2. ASSIGNMENT # 03
• Prepared by Amjad Khan
• Submitted to Dear, Sir Ghadir Ali
• Program BS Microbiology 3th
• Subject CELL BIOLOGY
• Topic CELL CYCLE
• Date 12th
January, 2015
2

3. 3
CellCell
ReproductionReproduction

4. 4
TypES of CEllTypES of CEll
REpRoduCTIoNREpRoduCTIoNAsexual reproductionAsexual reproduction involves ainvolves a
single cellsingle cell dividing to makedividing to make 2 new,2 new,
identical daughter cellsidentical daughter cells
Mitosis & binary fissionMitosis & binary fission areare
examples of asexual reproductionexamples of asexual reproduction
Sexual reproductionSexual reproduction involves twoinvolves two
cells (egg & sperm) joining to make acells (egg & sperm) joining to make a
new cell (zygote)new cell (zygote) that isthat is NOTNOT
identical to the original cellsidentical to the original cells
MeiosisMeiosis is an exampleis an example

5. Division Mechanisms
Prokaryotic organisms
– Binary fission
Eukaryotic organisms
– Mitosis
• Karyokinesis (division of nucleus)
• Cytokinesis (division of cytoplasm)
– Meiosis

6. 6
CEll dIvISIoN INCEll dIvISIoN IN
pRokARyoTESpRokARyoTES

7. 7
Cell Division in ProkaryotesCell Division in Prokaryotes
 Prokaryotes such asProkaryotes such as
bacteriabacteria divide into 2divide into 2
identical cells by theidentical cells by the
process ofprocess of binarybinary
fissionfission
 Single chromosomeSingle chromosome
makes a copy ofmakes a copy of
itselfitself
 Cell wall formsCell wall forms
between thebetween the
chromosomes dividingchromosomes dividing
the cellthe cell
ParentParent
cellcell
2 identical daughter cells2 identical daughter cells
ChromosomeChromosome
doublesdoubles
Cell splitsCell splits

8. 8
Prokaryotic CellProkaryotic Cell
Undergoing Binary FissionUndergoing Binary Fission

9. 9
Animation of Binary FissionAnimation of Binary Fission

10. 10
TheThe CellCell
CycleCycle

11. 11
Five Phases of the Cell CycleFive Phases of the Cell Cycle
GG11 - primary growth/gap phase- primary growth/gap phase
S – synthesis; DNA replicatedS – synthesis; DNA replicated
GG22 - secondary growth/gap- secondary growth/gap
phasephase
collectively these 3 stages arecollectively these 3 stages are
calledcalled interphaseinterphase
M - mitosisM - mitosis
C - cytokinesisC - cytokinesis

12. 12
Cell CycleCell Cycle

13. 13
Interphase - GInterphase - G11 StageStage
11stst
growth/gap stagegrowth/gap stage after cellafter cell
divisiondivision
CellsCells maturemature by making moreby making more
cytoplasm & organellescytoplasm & organelles
Cell carries on itsCell carries on its normalnormal
metabolic activitiesmetabolic activities i.e.i.e.
respiration, digestion etc.respiration, digestion etc.

14. 14
Interphase – S StageInterphase – S Stage
SynthesisSynthesis stagestage
DNADNA is copied oris copied or replicatedreplicated
TwoTwo
identicalidentical
copiescopies
of DNAof DNA
OriginalOriginal
DNADNA

15. 15
Interphase – GInterphase – G22 StageStage
22ndnd
Growth/GapGrowth/Gap StageStage
OccursOccurs after DNA has been copie;after DNA has been copie;
also in preparation for M phasealso in preparation for M phase
All cellAll cell structures needed forstructures needed for
divisiondivision are made (e.g. centrioles)are made (e.g. centrioles)
BothBoth organelles & proteinsorganelles & proteins areare
synthesizedsynthesized

16. 16
What’s Happening in Interphase?What’s Happening in Interphase?
What the cell looks likeWhat the cell looks like
Animal Cell
What’s occurring

17. 17
Sketch the Cell CycleSketch the Cell Cycle
DaughterDaughter
CellsCells
DNA CopiedDNA Copied
CellsCells
MatureMature
Cells prepare forCells prepare for
DivisionDivision
Cell Divides intoCell Divides into
Identical cellsIdentical cells

18. 18
MitosisMitosis

19. 19
MitosisMitosis
Division of theDivision of the
nucleusnucleus
(karyokinesis)(karyokinesis)
Division of theDivision of the
cytoplasmcytoplasm
(cytokinesis)(cytokinesis)
Only occurs inOnly occurs in
eukaryoteseukaryotes
HasHas fourfour stagesstages
Doesn’t occur inDoesn’t occur in
some cells such assome cells such as
brain cellsbrain cells

20. 20
Four Mitotic StagesFour Mitotic Stages
ProProphasephase
MetaMetaphasephase
AnaAnaphasephase
TeloTelophasephase

21. 21
Early ProphaseEarly Prophase
ChromatinChromatin in nucleus condenses toin nucleus condenses to
formform visible chromosomesvisible chromosomes
Mitotic spindleMitotic spindle forms from fibers informs from fibers in
cytoskeleton orcytoskeleton or centrioles (animal)centrioles (animal)
ChromosomesChromosomes
NucleolusNucleolus CytoplasmCytoplasm
Nuclear MembraneNuclear Membrane

22. 22
Late ProphaseLate Prophase
Nuclear membrane & nucleolusNuclear membrane & nucleolus areare
broken downbroken down
ChromosomesChromosomes continue condensing &continue condensing &
areare clearly visibleclearly visible
Spindle fibers calledSpindle fibers called kinetochoreskinetochores
attach to the centromereattach to the centromere of eachof each
chromosomechromosome
SpindleSpindle finishes forming between thefinishes forming between the
poles of the cellpoles of the cell

23. 23
Late ProphaseLate Prophase
Nucleus & Nucleolus have disintegratedNucleus & Nucleolus have disintegrated
ChromosomesChromosomes

24. 24
Spindle Fiber attached toSpindle Fiber attached to
ChromosomeChromosome
Kinetochore FiberKinetochore Fiber
ChromosomeChromosome

25. 25
Review of ProphaseReview of Prophase
What the cellWhat the cell
looks likelooks like
What’s happeningWhat’s happening

26. 26
Spindle FibersSpindle Fibers
The mitoticThe mitotic spindlespindle form from theform from the
microtubulesmicrotubules in plantsin plants andand centriolescentrioles
in animal cellsin animal cells
Polar fibersPolar fibers extend from one pole ofextend from one pole of
the cell to the opposite polethe cell to the opposite pole
Kinetochore fibersKinetochore fibers extend from theextend from the
pole to the centromere of thepole to the centromere of the
chromosome to which they attachchromosome to which they attach
AstersAsters are short fibers radiatingare short fibers radiating
from centriolesfrom centrioles

27. 27
Sketch The SpindleSketch The Spindle

28. 28
MetaphaseMetaphase
Chromosomes, attached to theChromosomes, attached to the
kinetochore fiberskinetochore fibers, move to the center, move to the center
of the cellof the cell
Chromosomes are now lined up at theChromosomes are now lined up at the
equatorequator
Pole ofPole of
the Cellthe Cell
Equator of CellEquator of Cell

29. 29
MetaphaseMetaphase
AsterAster
Chromosomes at EquatorChromosomes at Equator

30. 30
Review of MetaphaseReview of Metaphase
What the cell looksWhat the cell looks
likelike
What’sWhat’s
occurringoccurring

31. 31
AnaphaseAnaphase
OccursOccurs rapidlyrapidly
SisterSister
chromatidschromatids areare
pulled apart topulled apart to
opposite polesopposite poles
of the cell byof the cell by
kinetochorekinetochore
fibersfibers

32. 32
Anaphase ReviewAnaphase Review
What theWhat the
cell lookscell looks
likelike
What’sWhat’s
occurringoccurring

33. 33
TelophaseTelophase
Sister chromatids atSister chromatids at oppositeopposite
polespoles
SpindleSpindle disassemblesdisassembles
Nuclear envelopeNuclear envelope forms aroundforms around
each set of sister chromatidseach set of sister chromatids
NucleolusNucleolus reappearsreappears
CYTOKINESISCYTOKINESIS occursoccurs
Chromosomes reappear asChromosomes reappear as
chromatinchromatin

34. 34
Comparison of Anaphase & TelophaseComparison of Anaphase & Telophase

35. 35
CytokinesisCytokinesis
Means division of the cytoplasmMeans division of the cytoplasm
DivisionDivision of cell into two,of cell into two,
identical halves calledidentical halves called daughterdaughter
cellscells
In plant cells, cell plateIn plant cells, cell plate formsforms
at the equator to divide cellat the equator to divide cell
In animal cells,In animal cells, cleavage furrowcleavage furrow
forms to split cellforms to split cell

36. 36
CytokinesisCytokinesis
Cleavage furrowCleavage furrow
in animal cellin animal cell
Cell plate inCell plate in
animal cellanimal cell

37. 37
Mitotic StagesMitotic Stages

38. 38
Daughter Cells of MitosisDaughter Cells of Mitosis
Have theHave the same number ofsame number of
chromosomes as each otherchromosomes as each other and asand as
the parent cellthe parent cell from which theyfrom which they
were formedwere formed
IdenticalIdentical to each other, butto each other, but smallersmaller
than parent cellthan parent cell
MustMust grow in sizegrow in size to become matureto become mature
cellscells (G(G11 of Interphase)of Interphase)

39. 39
Identical Daughter CellsIdentical Daughter Cells
Chromosome number theChromosome number the samesame, but cells, but cells
smallersmaller than parent cellthan parent cell
What isWhat is
the 2nthe 2n
oror
diploiddiploid
number?number?
22

40. 40
ReviewReview
ofof
MitosisMitosis

41. 41
Draw & Learn these StagesDraw & Learn these Stages

42. 42
Draw & Learn these StagesDraw & Learn these Stages

43. 43
InterphaseInterphase
ProphaseProphase
MetaphaseMetaphase
AnaphaseAnaphase
TelophaseTelophase
Name the Mitotic Stages:Name the Mitotic Stages:
Name this?Name this?
Name this?Name this?

44. 44
Eukaryotic Cell DivisionEukaryotic Cell Division
 Used forUsed for growth andgrowth and
repairrepair
 Produce two new cellsProduce two new cells
identical to the originalidentical to the original
cellcell
 Cells areCells are diploid (2n)diploid (2n)
Chromosomes duringChromosomes during
Metaphase of mitosisMetaphase of mitosis
ProphaseProphase MetaphaseMetaphase AnaphaseAnaphase
TelophaseTelophase
CytokinesisCytokinesis

45. 45
Mitosis AnimationMitosis Animation
Name each stage as you see it occur?Name each stage as you see it occur?

46. 46
Mitosis in Onion Root TipsMitosis in Onion Root Tips
Do you see any stages of mitosis?Do you see any stages of mitosis?

47. 47
Locate the Four MitoticLocate the Four Mitotic
Stages in PlantsStages in Plants
MetaphaseMetaphase
ProphaseProphase
AnaphaseAnaphase
TelophaseTelophase

48. 48
Uncontrolled Mitosis
 If mitosis is notIf mitosis is not
controlledcontrolled, unlimited, unlimited
cell division occurscell division occurs
causing cancerouscausing cancerous
tumorstumors
 OncogenesOncogenes are specialare special
proteinsproteins that
increase the chanceincrease the chance
that a normal cellthat a normal cell
develops into adevelops into a tumortumor
cellcell
Cancer cellsCancer cells

49. 49
MeiosisMeiosis
Formation of GametesFormation of Gametes
(Eggs & Sperm)(Eggs & Sperm)

50. Words to knoW
Gametes - reproductive cells that unite during sexual
reproduction to form a new cell called a zygote (male = sperm,
female = egg cell)
Germ cells – sperm or egg cells
Somatic cells - any cell other than the reproductive cells
Diploid - a cell that contains two sets of chromosomes (2n), as
normally found in somatic cells
Haploid - have one set of chromosomes (n=1) as in germ cells,
or half as many as a somatic cell
Homologous – chromosomes that are alike in structure and
genes
Alleles – different forms of a gene ex. if talking about hair color
as the gene, different alleles would be different colors like red,
blonde, black etc. 50

51. 51
Facts About MeiosisFacts About Meiosis
Preceded by interphase whichPreceded by interphase which
includesincludes chromosome replicationchromosome replication
TwoTwo meiotic divisions:meiotic divisions: Meiosis IMeiosis I
and Meiosis IIand Meiosis II
AkaAka reduction-divisionreduction-division
Original cell is diploid (2n)Original cell is diploid (2n)
Four daughter cellsFour daughter cells produced thatproduced that
areare haploid (n)haploid (n)

52. 52
Facts About MeiosisFacts About Meiosis
Daughter cellsDaughter cells contain half the numbercontain half the number
of chromosomesof chromosomes as the original cellas the original cell
ProducesProduces gametesgametes (eggs & sperm(eggs & sperm))
Occurs in theOccurs in the testestestes in malesin males
((SpermatogenesisSpermatogenesis))
Occurs in theOccurs in the ovariesovaries in femalesin females
((OogenesisOogenesis))
Human diploid cells haveHuman diploid cells have 46 chromosomes46 chromosomes
(2n=46)(2n=46)
Human sperm and egg cells haveHuman sperm and egg cells have 2323
chromosomes (n=23) eachchromosomes (n=23) each

53. 53
 Start withStart with 46 double stranded46 double stranded
chromosomes (2n)chromosomes (2n)
After 1 division -After 1 division - 23 double23 double
stranded chromosomes (n)stranded chromosomes (n)
After 2nd division -After 2nd division - 23 single23 single
stranded chromosomes (n)stranded chromosomes (n)
 Occurs in ourOccurs in our germ cellsgerm cells
More Meiosis FactsMore Meiosis Facts

54. 54
Why Do we Need Meiosis?Why Do we Need Meiosis?
It is the fundamental basis ofIt is the fundamental basis of
sexual reproductionsexual reproduction
Two haploid (1n) gametes areTwo haploid (1n) gametes are
brought together throughbrought together through
fertilizationfertilization to form a diploidto form a diploid
(2n) zygote(2n) zygote

55. 55
Fertilization – “Putting itFertilization – “Putting it
all together”all together”
1n =31n =3
2n = 62n = 6

56. 56
Replication of ChromosomesReplication of Chromosomes
ReplicationReplication is theis the
process ofprocess of
duplicating aduplicating a
chromosomechromosome
OccursOccurs prior toprior to
divisiondivision
Replicated copiesReplicated copies
are calledare called sistersister
chromatidschromatids
Held together atHeld together at
centromerecentromere
Occurs inOccurs in
InterphaseInterphase

57. 57
A Replicated ChromosomeA Replicated Chromosome
HomologuesHomologues
(same genes,(same genes,
different alleles)different alleles)
SisterSister
ChromatidsChromatids
(same genes,(same genes,
same alleles)same alleles)
Gene XGene X
Homologues separate in meiosis I andHomologues separate in meiosis I and
therefore different alleles separate.therefore different alleles separate.

58. 58
Meiosis Forms Haploid GametesMeiosis Forms Haploid Gametes
 Meiosis mustMeiosis must reduce the chromosome numberreduce the chromosome number
by halfby half
 Fertilization then restoresFertilization then restores the 2n numberthe 2n number
from mom from dad child
meiosis reduces
genetic content
too
much!
The right
number!

59. 59
Meiosis: Two Part CellMeiosis: Two Part Cell
DivisionDivision
HomologuesHomologues
separateseparate
SisterSister
chromatidschromatids
separateseparate
DiploidDiploid
MeiosisMeiosis
II
MeiosisMeiosis
IIII
DiploidDiploid
HaploidHaploid

60. 60
Meiosis I: Reduction DivisionMeiosis I: Reduction Division
NucleusNucleus SpindleSpindle
fibersfibers NuclearNuclear
envelopeenvelopeEarlyEarly
Prophase IProphase I
(Chromosome(Chromosome
numbernumber
doubleddoubled))
LateLate
ProphaseProphase
II
MetaphaseMetaphase
II AnaphaseAnaphase
II
Telophase ITelophase I
(diploid)(diploid)

61. 61
Prophase IProphase I
Early prophaseEarly prophase
HomologuesHomologues
pair.pair.
Crossing overCrossing over
occursoccurs.
Late prophaseLate prophase
Chromosomes condense.Chromosomes condense.
Spindle forms.Spindle forms.
Nuclear envelopeNuclear envelope
fragments.fragments.

62. 62
Tetrads Form in Prophase ITetrads Form in Prophase I
Homologous chromosomesHomologous chromosomes
(each with sister chromatids)(each with sister chromatids)
Join to form aJoin to form a
TETRADTETRAD
Called SynapsisCalled Synapsis

63. 63
Crossing-OverCrossing-Over
 HomologousHomologous
chromosomeschromosomes in ain a
tetradtetrad cross overcross over
each othereach other
 Pieces ofPieces of
chromosomes orchromosomes or
genes aregenes are
exchangedexchanged
 ProducesProduces GeneticGenetic
recombinationrecombination inin
the offspringthe offspring
•Occurs in nonsister chromatids
•Increases genetic variability
Genetic recombination in
which a strand of the genetic
material (DNA/RNA)is broken
and then joined to the end of
a different DNA molecule.

64. 64
Homologous ChromosomesHomologous Chromosomes
During Crossing-OverDuring Crossing-Over

65. 65
Crossing-over multiplies the already hugeCrossing-over multiplies the already huge
number of different gamete typesnumber of different gamete types
produced by independent assortmentproduced by independent assortment
Crossing-OverCrossing-Over

66. 66
Metaphase IMetaphase I
Homologous pairsHomologous pairs
of chromosomesof chromosomes
align along thealign along the
equatorequator of theof the
cellcell

67. 67
Anaphase IAnaphase I
Homologues separateHomologues separate andand
move to opposite poles.move to opposite poles.
Sister chromatidsSister chromatids remainremain
attachedattached at theirat their
centromerescentromeres.

68. 68
Telophase ITelophase I
Nuclear envelopesNuclear envelopes
reassemble.reassemble.
Spindle disappears.Spindle disappears.
CytokinesisCytokinesis divides celldivides cell
into two.into two.

69. 69
Meiosis IIMeiosis II
Only one homologue of eachOnly one homologue of each
chromosome is present inchromosome is present in
the cellthe cell.
Meiosis II produces gametes withMeiosis II produces gametes with
one copy of each chromosome andone copy of each chromosome and
thus one copy of each gene.thus one copy of each gene.
Sister chromatids carrySister chromatids carry
identical geneticidentical genetic
informationinformation..
Gene XGene X

70. 70
Meiosis II: ReducingMeiosis II: Reducing
Chromosome NumberChromosome Number
ProphaseProphase
IIII
MetaphaseMetaphase
IIII
AnaphaseAnaphase
IIII
TelophaseTelophase
IIII 4 Identical4 Identical
haploid cellshaploid cells

71. 71
Prophase IIProphase II
Nuclear envelopeNuclear envelope
fragments.fragments.
Spindle forms.Spindle forms.

72. 72
Metaphase IIMetaphase II
Chromosomes alignChromosomes align
alongalong equatorequator of cellof cell..

73. 73
Anaphase IIAnaphase II
Sister chromatidsSister chromatids
separate andseparate and
move tomove to oppositeopposite
polespoles.
EquatorEquator
PolePole

74. 74
Telophase IITelophase II
Nuclear envelopeNuclear envelope
assembles.assembles.
ChromosomesChromosomes
decondense.decondense.
Spindle disappears.Spindle disappears.
Cytokinesis dividesCytokinesis divides
cell into two.cell into two.

75. 75
Results of MeiosisResults of Meiosis
Gametes (egg & sperm)Gametes (egg & sperm)
formform
Four haploid cells withFour haploid cells with
one copy of eachone copy of each
chromosomechromosome
One allele of each geneOne allele of each gene
Different combinations ofDifferent combinations of
alleles for differentalleles for different
genes along thegenes along the
chromosomechromosome

76. 76
GametogenesisGametogenesis
OogenesisOogenesis
oror
SpermatogenesisSpermatogenesis

77. 77
SpermatogenesisSpermatogenesis
Occurs in theOccurs in the
testestestes
Two divisionsTwo divisions
produce 4produce 4
spermatidsspermatids
SpermatidsSpermatids maturemature
into sperminto sperm
Men produce aboutMen produce about
250,000,000250,000,000
sperm per daysperm per day

78. 78
Spermatogenesis in theSpermatogenesis in the
TestesTestes
SpermatidSpermatid

79. 79
SpermatogenesisSpermatogenesis

80. 80
OogenesisOogenesis
Occurs in theOccurs in the ovariesovaries
Two divisions produceTwo divisions produce 3 polar bodies3 polar bodies
that die andthat die and 1 egg1 egg
Polar bodies die because ofPolar bodies die because of unequalunequal
division of cytoplasmdivision of cytoplasm
Immature egg calledImmature egg called oocyteoocyte
Starting at puberty, one oocyteStarting at puberty, one oocyte
matures into anmatures into an ovum (egg)ovum (egg) every 28every 28
daysdays

81. 81
Oogenesis in the OvariesOogenesis in the Ovaries

82. 82
OogenesisOogenesis
OogoniumOogonium
(diploid)(diploid)
MitosisMitosis
PrimaryPrimary
oocyteoocyte
(diploid)(diploid)
Meiosis IMeiosis I
SecondarySecondary
oocyteoocyte
(haploid)(haploid)
Meiosis IIMeiosis II
(if fertilization(if fertilization
occurs)occurs)
First polar bodyFirst polar body
may dividemay divide
(haploid)(haploid)
PolarPolar
bodiesbodies
diedie
Ovum (egg)Ovum (egg)
SecondSecond
polar bodypolar body
(haploid)(haploid)
a
A
X
X
a
X
A X
a
X
a
X
MatureMature
eggegg
A
X
A
X

83. 83
ComparingComparing
Mitosis andMitosis and
MeiosisMeiosis

84. 84
MitosisMitosis MeiosisMeiosis
Number ofNumber of
divisionsdivisions
11
22
Number ofNumber of
daughter cellsdaughter cells
22 44
GeneticallyGenetically
identical?identical?
YesYes NoNo
Chromosome #Chromosome # Same as parentSame as parent Half of parentHalf of parent
WhereWhere Somatic cellsSomatic cells Reproductive cellsReproductive cells
WhenWhen Throughout lifeThroughout life At sexual maturityAt sexual maturity
RoleRole Growth andGrowth and
repairrepair
Sexual reproductionSexual reproduction
Comparison of DivisionsComparison of Divisions

85. 85
Meiosis Mitosis
Definition:
A type of cellular reproduction in
which the number of chromosomes
are reduced by half through the
separation of homologous
chromosomes in a diploid cell.
A process of asexual reproduction
in which the cell divides in two
producing a replica, with an equal
number of chromosomes in haploid
cell
Function: sexual reproduction
Cellular Reproduction & general
growth and repair of the body
Type of Reproduction: Sexual Asexual
Occurs in: Humans, animals, plants, fungi all organisms
Genetically: different identical
Crossing Over:
Yes, mixing of chromosomes can
occur.
No, crossing over cannot occur.
Pairing of Homologues: Yes No
Number of Divisions: 2 1
Number of Haploid Daughter Cells
produced:
4 2
Chromosome Number: Reduced by half Remains the same
Steps:
The steps of meiosis are
Interphase, Prophase I, Metaphase
I, Anaphase I, Telophase I,
Prophase II, Metaphase II,
Anaphase II and Telophase II.
The steps of mitosis are
Interphase, Prophase, Metaphase,
Anaphase, Telophase and
Cytokinesis
Karyokenesis: Occurs in Interphase I Occurs in Interphase
Cytokenesis:
Occurs in Telophase I & Telohpase
II
Occurs in Telophase
Centromeres Split:
The centromeres do not separate
during anaphase I, but during
anaphase II
The centromeres split during
Anaphase
Creates:
Sex cells only: Female egg cells or Makes everything other than sex

86. End…..
86