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Reproduc)onattheCellularLevelBIOL160

Ch. 6

The Key Roles of Cell Division

•  Celldivision

•  Cellularreproduc)on

•  Anabilityoforganismsthatbestdis)nguisheslivingthingsfrom

nonlivingmaAer

•  Unicellularorganisms

•  Cellulardivisionreproducestheen)reorganism

•  Mul)cellularorganisms

•  dependoncelldivisionfor:

•  Developmentfromafer)lizedcell•  Growth•  Repair

•  Cellcycle

•  Lifeofacellfromforma)ontoitsowndivision

•  Celldivisionisanintegralpart100 µm 200 µm 20 µm

(a) Reproduction (b) Growth and development

(c) Tissue renewal

Cell Division

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•  Genome

•  AlltheDNAinacell

•  MaybeasingleDNAmolecule

•  prokaryo)ccells

or…

•  ManyDNAmolecules

•  eukaryo)ccells

•  Chromosomes

•  PackagedDNAmoleculesinacell

•  OnemoleculeofDNAequalsonechromosome

•  Humanaverage51million-245millionbasepairsperchromosome

Cellular Organization of the Genetic Material

•  Eacheukaryo)cspecies

•  Hasacharacteris)cnumberofchromosomesineachcellnucleus

•  Soma3ccells

•  Non-reproduc)vecells

•  havetwoofeachtypeofchromosome

•  Diploid-46

•  Germcells

•  MakeGametes

•  Reproduc)vecells:spermandeggs

•  Onlyoneofeachchromosome

•  Haploid-23

Cellular Organization of the Genetic Material

•  Chroma3n

•  ComplexofDNAandproteinthatcondensesduringcelldivision

•  InEukaryo)cchromosomes

•  TypicalDNAformwhennotac)velydividing

DNA Packaging

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•  Prepara)onforcelldivision

•  DNAisreplicatedandthe

chromosomescondense

•  Sisterchroma3ds

•  Duplicatedchromosome

•  Twocopieswhichseparate

duringcelldivision

•  Centromere

•  Junc)onpointoftheduplicated

chromosome,wherethetwo

chroma)dsareaAached

Chromosome Distribution During Cell Division

Fig.12-4

0.5 µm Chromosomes

Chromosome duplication (including DNA synthesis)

Chromo- some arm

Centromere

Sister chromatids

DNA molecules

Separation of sister chromatids

Centromere

Sister chromatids

•  Eukaryo)ccelldivisionconsistsof:

•  Mitosis

•  Divisionoftheduplicatedgenome

•  Cytokinesis

•  Divisionofthecytoplasmandsepara)onoforganelles

•  Meiosis

•  Avaria)onofcelldivisionformakinggametes

•  Yieldsnoniden)caldaughtercells

•  Onlyonesetofchromosomes,halfasmanyastheparentcell

•  Haploid

Types of Eukaryotic Cell Division

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Phases of the Cell Cycle

•  Thecellcycleconsistsof2phases

•  Mito3c(M)phase

•  mitosisandcytokinesis

•  Interphase

•  cellgrowth

•  copyingofchromosomes

inprepara)onforcell

division

•  Interphase

•  about90%ofthecellcycle

•  canbedividedinto

subphases:

•  G1phase

•  firstgap

•  Sphase

•  Synthesisof

duplicateDNA

•  G2phase

•  secondgap

Phases of the Cell Cycle - Interphase

S (DNA synthesis)

MITOTIC (M) PHASE

Mito

sis

Cytokinesis

G1

G2

•  Mitosisisconven)onallydividedintofive

phases:

•  Prophase

•  Prometaphase

•  Metaphase

•  Anaphase

•  Telophase

•  Cytokinesisiswellunderwaybylate

telophase

Phases of the Cell Cycle - Mitotic Phase

PLAY

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Fig.12-6

G2 of Interphase

Centrosomes (with centriole pairs)

Chromatin (duplicated)

Nucleolus Nuclear envelope

Plasma membrane

Early mitotic spindle

Aster Centromere

Chromosome, consisting of two sister chromatids

Prophase Prometaphase

Fragments of nuclear envelope

Nonkinetochore microtubules

Kinetochore Kinetochore microtubule

Metaphase

Metaphase plate

Spindle Centrosome at one spindle pole

Anaphase

Daughter chromosomes

Telophase and Cytokinesis

Cleavage furrow

Nucleolus forming

Nuclear envelope forming

Phases of the Cell Cycle - Mitotic Phase

Prophase Prometaphase G2 of Interphase

Interphase

Prometaphase Prophase G2 of Interphase Nonkinetochore microtubules

Fragments of nuclear envelope

Aster Centromere Early mitotic spindle

Chromatin (duplicated)

Centrosomes (with centriole pairs)

Nucleolus Nuclear envelope

Plasma membrane

Chromosome, consisting of two sister chromatids

Kinetochore Kinetochore microtubule

•  Interphase(G2)

•  Diffusechroma)n

•  duplicatedstate

•  Chromosomes

notvisibleunder

lightmicroscope

•  Nucleoluss)ll

present

Prophase Prometaphase G2 of Interphase

Prometaphase Prophase G2 of Interphase

Nonkinetochore microtubules

Fragments of nuclear envelope

Aster Centromere Early mitotic spindle

Chromatin (duplicated)

Centrosomes (with centriole pairs)

Nucleolus Nuclear envelope

Plasma membrane

Chromosome, consisting of two sister chromatids

Kinetochore Kinetochore microtubule

•  Prophase

•  Chroma)nbegins

tocondense

•  Centrosomesbegin

tomigrate

•  Spindlebeginsto

grow

Prophase

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Prophase Prometaphase G2 of Interphase

Prometaphase Prophase G2 of Interphase

Nonkinetochore microtubules

Fragments of nuclear envelope

Aster Centromere Early mitotic spindle

Chromatin (duplicated)

Centrosomes (with centriole pairs)

Nucleolus Nuclear envelope

Plasma membrane

Chromosome, consisting of two sister chromatids

Kinetochore Kinetochore microtubule

•  Prometaphase

•  Chromsomesfullycondensed

•  Nuclearmembranebrokendown

•  Centrosomesestablishpoles

•  SpindlefibersaAachtokinetochores

Prometaphase

Fig.12-6c

Metaphase Anaphase Telophase and Cytokinesis

Metaphase Anaphase Telophase and Cytokinesis

Cleavage furrow

Nucleolus forming

Metaphase plate

Centrosome at one spindle pole

Spindle Daughter chromosomes

Nuclear envelope forming

•  Metaphase

•  Chromosomesline

upatmetaphase

plate

•  Singlefile

•  Guidedby

spindlefibers

Metaphase

Fig.12-6c

Metaphase Anaphase Telophase and Cytokinesis

Metaphase Anaphase Telophase and Cytokinesis

Cleavage furrow

Nucleolus forming

Metaphase plate

Centrosome at one spindle pole

Spindle Daughter chromosomes

Nuclear envelope forming

•  Anaphase

•  Sisterchroma)ds

separate

•  Now

daughter

chromosomes

•  Migratetopoles

•  Spindlefibers

shorten

Anaphase

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Fig.12-6c

Metaphase Anaphase Telophase and Cytokinesis

Metaphase Anaphase Telophase and Cytokinesis

Cleavage furrow

Nucleolus forming

Metaphase plate

Centrosome at one spindle pole

Spindle Daughter chromosomes

Nuclear envelope forming

•  Telophase

•  Daughter

chromosomes

reachpoles

•  Beginto

decondense

•  Nuclear

membranesform

•  Cytokinesisbegins

•  Cleavagefurrow

forms

Telophase

The Mitotic Spindle: A Closer Look •  Mito3cspindle

•  Apparatusofmicrotubulesthatcontrols

chromosomemovementduringmitosis

•  Centrosome

•  Microtubuleorganizingcenter

•  Consistsoftwocentrioles

•  Duringprophaseassemblesspindle

microtubules

•  Thecentrosomereplicates

•  formingtwocentrosomes

•  migratetooppositeendsofthecell

•  spindlemicrotubulesgrowoutfrom

them

Cytokinesis: A Closer Look

•  Animalcells

•  cytokinesisoccursbycleavage,formingacleavagefurrow

•  Plantcells

•  acellplateformsduringcytokinesis

Cleavage furrow 100 µm

Contractile ring of microfilaments

Daughter cells

(a) Cleavage of an animal cell (SEM) (b) Cell plate formation in a plant cell (TEM)

Vesicles forming cell plate

Wall of parent cell

Cell plate

Daughter cells

New cell wall

1 µm

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Sea Urchin (Time Lapse)

Animal Mitosis

PLAY

PLAY

Mitosis and Cytokinesis

Binary Fission

•  Prokaryotes(EubacteriaandArchaebacteria)

•  Reproducebyatypeofcelldivisioncalledbinaryfission

•  Singlechromosomereplicates(beginningattheoriginof

replica3on)

•  twodaughterchromosomesac)velymoveapart

Fig.12-11-1

Origin of replication

Two copies of origin

E. coli cell Bacterial chromosome

Plasma membrane

Cell wall

Binary Fission

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Fig.12-11-2

Origin of replication

Two copies of origin

E. coli cell Bacterial chromosome

Plasma membrane

Cell wall

Origin Origin

Binary Fission

Fig.12-11-3

Origin of replication

Two copies of origin

E. coli cell Bacterial chromosome

Plasma membrane

Cell wall

Origin Origin

Binary Fission

Fig.12-11-4

Origin of replication

Two copies of origin

E. coli cell Bacterial chromosome

Plasma membrane

Cell wall

Origin Origin

Binary Fission

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Regulation of the Cell Cycle

•  Thefrequencyofcelldivisionvarieswiththe

typeofcell

•  Musclecells

•  Neurons

•  Hepatocytes

•  Thesecellcycledifferencesresultfrom

regula)onatthemolecularlevel

•  Signalingmolecules

The Cell Cycle Control System

S G1

M checkpoint

G2 M

Control system

G1 checkpoint

G2 checkpoint

•  Cellcyclecontrolsystem

•  Regulatedbybothinternalandexternalcontrols

•  Hasspecificcheckpointswherethecellcyclestopsun)lago-ahead

signalisreceived

•  G1checkpoint

•  Appearsmostimportant

•  cellreceivesago-aheadsignalattheG1checkpoint,itwillusuallycompletetheS,G2,andMphasesanddivide

•  Nogo-aheadsignal

•  Cellsexitscycle,switchingintoG0phase-anon-dividingstate

The Cell Cycle Control System

G1

G0

G1 checkpoint

(a)  Cell receives a go-ahead signal

G1

(b) Cell does not receive a go-ahead signal

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Stop/Go Signs: Signals at the Checkpoints

•  Internalsignal

•  Mcheckpoint

•  kinetochoresnotaAachedtospindlemicrotubules

•  sendamolecularsignalthatdelaysanaphase

•  Externalsignals

•  Growthfactors

•  proteinsreleasedbycertaincellsthats)mulateothercellstodivide

•  platelet-derivedgrowthfactor(PDGF)s)mulatesthedivisionof

humanfibroblastcellsinculture

•  Otherexternalsignals

•  density-dependentinhibi3on

•  crowdedcellsstopdividing

•  anchoragedependence

•  MostanimalcellsmustbeaAachedtoasubstratuminordertodivide

Stop/Go Signs: Signals at the Checkpoints

Anchorage dependence

Density-dependent inhibition

Density-dependent inhibition

(a) Normal mammalian cells (b) Cancer cells 25 µm 25 µm

Tumor

A tumor grows from a single cancer cell.

Glandular tissue

Lymph vessel

Blood vessel

Metastatic tumor

Cancer cell

Cancer cells invade neigh- boring tissue.

Cancer cells spread to other parts of the body.

Cancer cells may survive and establish a new tumor in another part of the body.

1 2 3 4

•  Transforma3on•  Anormalcellisconvertedtoacancerouscellwhichformstumors

•  massesofabnormalcellswithinotherwisenormal)ssue•  Benigntumor

•  Abnormalcellsremainattheoriginalsite•  Malignanttumors

•  Invadesurrounding)ssues•  Canmetastasizeexpor)ngcancercellstootherpartsofthebody,possiblyform

secondarytumors

Loss of Cell Cycle Controls in Cancer Cells

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You should now be able to: 1.  Describethestructuralorganiza)onoftheprokaryo)cgenomeandtheeukaryo)c

genome

2.  Listthephasesofthecellcycle;describethesequenceofeventsduringeachphase

3.  Listthephasesofmitosisanddescribetheeventscharacteris)cofeachphase

4.  Drawordescribethemito)cspindle,includingcentrosomes,kinetochore

microtubules,nonkinetochoremicrotubules,andasters

5.  Comparecytokinesisinanimalsandplants

6.  Describetheprocessofbinaryfissioninbacteriaandexplainhoweukaryo)cmitosis

mayhaveevolvedfrombinaryfission

7.  Explainhowtheabnormalcelldivisionofcancerouscellsescapesnormalcellcycle

controls

8.  Dis)nguishbetweenbenign,malignant,andmetasta)ctumors