The Cell Cycle Chapter 09. The Cell Cycle Outline Interphase Mitotic Stage Cell Cycle Control ...

The Cell CycleChapter 09

The Cell The Cell CycleCycle

OutlineOutline

The Cell CycleThe Cell Cycle InterphaseInterphaseMitotic StageMitotic StageCell Cycle ControlCell Cycle ControlApoptosisApoptosis

Mitosis & CytokinesisMitosis & Cytokinesis

Mitosis in Animal CellsMitosis in Animal Cells

The Cell Cycle & CancerThe Cell Cycle & Cancer

Prokaryotic Cell DivisionProkaryotic Cell Division

2


The Cell CycleThe Cell Cycle

An orderly set of stages and substages An orderly set of stages and substages between one division and the nextbetween one division and the next

Just prior to next division:Just prior to next division:The cell grows largerThe cell grows larger

The number of organelles doublesThe number of organelles doubles

The DNA is replicatedThe DNA is replicated

The two major stages of the cell cycle:The two major stages of the cell cycle: Interphase, andInterphase, and

MitosisMitosis

3


InterphaseInterphase

Most of the cell cycle is spent in interphaseMost of the cell cycle is spent in interphaseGG11 Phase: Phase: Recovery from previous divisionRecovery from previous division Cell doubles its organellesCell doubles its organelles Accumulates raw materials for DNA synthesisAccumulates raw materials for DNA synthesis

S Phase:S Phase: DNA replication (synthesis)DNA replication (synthesis) Chromosomes enter with 1 chromatid eachChromosomes enter with 1 chromatid each Chromosomes leave with 2 identical chromatids Chromosomes leave with 2 identical chromatids eacheach

GG22 Phase: Phase: Between DNA replication and onset of mitosisBetween DNA replication and onset of mitosis Cell synthesizes proteins necessary for divisionCell synthesizes proteins necessary for division

4


Mitotic (M) StageMitotic (M) Stage

Includes:Includes:

Mitosis (karyokinesis)Mitosis (karyokinesis)

Nuclear divisionNuclear division

Daughter chromosomes distributed to two Daughter chromosomes distributed to two daughter nucleidaughter nuclei

CytokinesisCytokinesis

Cytoplasm divisionCytoplasm division

Results in two genetically identical daughter Results in two genetically identical daughter cellscells

5


Cell Cycle ControlCell Cycle Control

Cell cycle controlled by internal and external Cell cycle controlled by internal and external signalssignalsExternal signalsExternal signals Growth factorsGrowth factors Received at the plasma membraneReceived at the plasma membrane Cause completion of cell cycleCause completion of cell cycle

Internal signalsInternal signals Family of proteins called cyclinsFamily of proteins called cyclins Increase and decrease as cell cycle continuesIncrease and decrease as cell cycle continuesWithout them cycle stops at GWithout them cycle stops at G11, M or G, M or G22

Allows time for any damage to be repairedAllows time for any damage to be repaired

6


ApoptosisApoptosisOften defined as programmed cell deathOften defined as programmed cell deathMitosis and apoptosis are opposing forcesMitosis and apoptosis are opposing forces

Mitosis increases cell numberMitosis increases cell numberApoptosis decreases cell numberApoptosis decreases cell number

Cells harbor apoptosis enzymes (caspases)Cells harbor apoptosis enzymes (caspases)Ordinarily held in check by inhibitorsOrdinarily held in check by inhibitorsCan be unleashed by internal or external Can be unleashed by internal or external signalssignals

Signal protein P53Signal protein P53Stops cycle at GStops cycle at G11 when DNA damaged when DNA damaged Initiates DNA attempt at repairInitiates DNA attempt at repair If successful, cycle continues to mitosisIf successful, cycle continues to mitosis If not, apoptosis is initiatedIf not, apoptosis is initiated

7

8Apoptosis

The Cell The Cell CycleCycleMitosis:Mitosis:

PreparationPreparation

DNA is in very long threadsDNA is in very long threads ChromosomesChromosomes Stretched out and intertangled between divisionsStretched out and intertangled between divisions DNA is associated with histone proteinsDNA is associated with histone proteins Collectively called chromatinCollectively called chromatin

Before mitosis begins:Before mitosis begins: Chromatin condenses (coils) into distinctly visible Chromatin condenses (coils) into distinctly visible

chromosomeschromosomes Each species has a characteristic chromosome Each species has a characteristic chromosome

numbernumber Humans 46Humans 46 Corn 20Corn 20 Goldfish 94Goldfish 94

9


Chromosome NumberChromosome Number

Most familiar organisms diploidMost familiar organisms diploidHave two chromosomes of each typeHave two chromosomes of each type

Humans have 23 different types of Humans have 23 different types of chromosomeschromosomes Each type is represented twice in each body cell Each type is represented twice in each body cell (Diploid)(Diploid) Only sperm and eggs have one of each type Only sperm and eggs have one of each type (haploid)(haploid)

The The nn number for humans is number for humans is nn=23=23 Two representatives of each typeTwo representatives of each typeMakes a total of 2Makes a total of 2nn=46 in each nucleus=46 in each nucleus

One set of 23 from individual’s father (paternal)One set of 23 from individual’s father (paternal) Other set of 23 from individual’s mother Other set of 23 from individual’s mother

(maternal)(maternal)

10

11Chromosome Numbers

of Some Eukaryotes


Chromosome StructureChromosome Structure

At end of S phase:At end of S phase:Each chromosome internally duplicatedEach chromosome internally duplicatedConsists of two identical DNA chainsConsists of two identical DNA chains Sister chromatidsSister chromatids Attached together at a single point (centromere)Attached together at a single point (centromere)

Attached to each other atAttached to each other atDuring mitosis:During mitosis:

Centromeres holding sister chromatids Centromeres holding sister chromatids together simultaneously breaktogether simultaneously break

Sister chromatids separate Sister chromatids separate Each becomes a daughter chromosomeEach becomes a daughter chromosomeSisters of each type distributed to opposite Sisters of each type distributed to opposite daughter nucleidaughter nuclei

12

13Duplicated Chromosome



Just outside nucleus is the centrosomeJust outside nucleus is the centrosomeThis is the microtubule organizing centerThis is the microtubule organizing centerOrganizes the mitotic spindleOrganizes the mitotic spindle Contains many fibersContains many fibers Each composed of a bundle of microtubulesEach composed of a bundle of microtubules

In animals, contains two barrel-shaped In animals, contains two barrel-shaped centriolescentrioles Oriented at right angles to each other within Oriented at right angles to each other within centrosomecentrosome Each with 9 triplets of microtubules arranged in Each with 9 triplets of microtubules arranged in a cylindera cylinder

Centrosome was also replicated in S-phase, Centrosome was also replicated in S-phase, so now two centrosomesso now two centrosomes

14

The Cell The Cell CycleCycleMitosis in Animal Cells:Mitosis in Animal Cells:

ProphaseProphase

ProphaseProphaseChromatin has condensedChromatin has condensed Chromosomes distinguishable with microscopeChromosomes distinguishable with microscope

Visible double (two sister chromatids attached Visible double (two sister chromatids attached at centromere)at centromere)

Nucleolus disappearsNucleolus disappearsNuclear envelope disintegratesNuclear envelope disintegratesSpindle begins to take shapeSpindle begins to take shapeTwo centrosomes move away from each otherTwo centrosomes move away from each otherForm microtubules in star-like arrays – astersForm microtubules in star-like arrays – asters

15

16Mitosis in Animals


PrometaphasePrometaphase

PrometaphasePrometaphase

Centromere of each chromosome develops Centromere of each chromosome develops two kinetochorestwo kinetochores

Specialized protein complexSpecialized protein complex

One over each sister chromatidOne over each sister chromatid

Physically hook sister chromatids up with Physically hook sister chromatids up with specialized microtubules (kinetochore fibers)specialized microtubules (kinetochore fibers)

These connect sisters to opposite poles of These connect sisters to opposite poles of mother cellmother cell

17


Metaphase & AnaphaseMetaphase & Anaphase

MetaphaseMetaphase Chromosomes are pulled around by kinetochore Chromosomes are pulled around by kinetochore

fibersfibers Forced to align across equatorial plane of cellForced to align across equatorial plane of cell Appear to be spread out on a piece of glassAppear to be spread out on a piece of glass Metaphase plateMetaphase plate Represents plane through which mother cell will be Represents plane through which mother cell will be

divideddivided

AnaphaseAnaphase Centromere dissolves, releasing sister chromatidsCentromere dissolves, releasing sister chromatids Sister chromatids separateSister chromatids separate Now called daughter chromosomesNow called daughter chromosomes Pulled to opposite poles along kinetochore fibersPulled to opposite poles along kinetochore fibers

18


TelophaseTelophase

TelophaseTelophase

Spindle disappearsSpindle disappears

Now two clusters of daughter chromosomesNow two clusters of daughter chromosomes

Still two of each type with all types representedStill two of each type with all types represented

Clusters are incipient daughter nucleiClusters are incipient daughter nuclei

Nuclear envelopes form around the two Nuclear envelopes form around the two incipient daughter nucleiincipient daughter nuclei

Chromosomes uncoil and become diffuse Chromosomes uncoil and become diffuse chromatin againchromatin again

Nucleolus reappears in each daughter nucleusNucleolus reappears in each daughter nucleus

19

The Cell The Cell CycleCycleCytokinesis:Cytokinesis:

Animal CellsAnimal Cells

Division of cytoplasmDivision of cytoplasmAllocates mother cell’s cytoplasm equally to Allocates mother cell’s cytoplasm equally to

daughter nucleusdaughter nucleusEncloses each in it’s own plasma membraneEncloses each in it’s own plasma membraneOften begins in anaphaseOften begins in anaphaseAnimal cytokinesis:Animal cytokinesis:

A cleavage furrow appears between daughter A cleavage furrow appears between daughter nucleinuclei

Formed by a contractile ring of actin filamentsFormed by a contractile ring of actin filamentsLike pulling on a draw stringLike pulling on a draw stringEventually pinches mother cell in twoEventually pinches mother cell in two

20

21Cytokinesis in Animal Cells

The Cell The Cell CycleCycleCytokinesis:Cytokinesis:

Plant CellsPlant Cells

Rigid cell walls outside plasma membrane do Rigid cell walls outside plasma membrane do not permit furrowingnot permit furrowing

Begins with formation of a cell plateBegins with formation of a cell plateMany small membrane-bounded vesiclesMany small membrane-bounded vesiclesEventually fuse into one thin vesicle Eventually fuse into one thin vesicle extending across the mother cellextending across the mother cell

The membranes of the cell plate become the The membranes of the cell plate become the plasma membrane between the daughter cellsplasma membrane between the daughter cells Contents of vesicles become the middle lamella Contents of vesicles become the middle lamella between the two daughter cellsbetween the two daughter cells Daughter cells later secrete primary cell walls Daughter cells later secrete primary cell walls on opposite sides of middle lamellaon opposite sides of middle lamella

22

23Cytokinesis in Plant Cells


The Cell Cycle and CancerThe Cell Cycle and Cancer

Abnormal growth of cells is called a neoplasmAbnormal growth of cells is called a neoplasm Benign neoplasms are not cancerousBenign neoplasms are not cancerous EncapsulatedEncapsulated Do not invade neighboring tissue or spreadDo not invade neighboring tissue or spread

Malignant neoplasms are cancerousMalignant neoplasms are cancerous Not encapsulatedNot encapsulated Readily invade neighboring tissuesReadily invade neighboring tissues May also detach and lodge in distant places – May also detach and lodge in distant places –

metastasismetastasis Results from mutation of genes regulating the cell cycleResults from mutation of genes regulating the cell cycle

Carcinogenesis – development of cancerCarcinogenesis – development of cancer Tends to be gradualTends to be gradual May be years before cell is obviously cancerousMay be years before cell is obviously cancerous

24


Characteristics of Cancer CellsCharacteristics of Cancer Cells

Lack differentiationLack differentiationHave abnormal nucleiHave abnormal nucleiForm tumorsForm tumors

Mitosis controlled by contact with neighboring Mitosis controlled by contact with neighboring cells – contact inhibitioncells – contact inhibition

Cancer cells have lost contact inhibitionCancer cells have lost contact inhibitionUndergo metastasisUndergo metastasis

Original tumor easily fragmentsOriginal tumor easily fragmentsNew tumors appear in other organsNew tumors appear in other organs

Undergo angiogenesisUndergo angiogenesisFormation of new blood vesselsFormation of new blood vessels

25

26Cancer Cells Versus Normal Cells

27Cancer Cells

The Cell The Cell CycleCycleOrigins of Cancer:Origins of Cancer:

OncogenesOncogenes

Mutations in DNA repair mechanismsMutations in DNA repair mechanisms

OncogenesOncogenes

Proto-oncogenes promote the cell cycle in Proto-oncogenes promote the cell cycle in various waysvarious ways

Tumor suppressor genes inhibit the cell cycle Tumor suppressor genes inhibit the cell cycle in various waysin various ways

Both normally regulated in coordination with Both normally regulated in coordination with organism’s growth planorganism’s growth plan

If either mutates, may lose control and If either mutates, may lose control and become oncogenebecome oncogene

28

The Cell The Cell CycleCycleOrigins of Cancer:Origins of Cancer:

TelomeraseTelomerase

Chromosomes normally have special material Chromosomes normally have special material at each end called telomeres (end parts)at each end called telomeres (end parts)

These get shorter each cell divisionThese get shorter each cell divisionWhen they get very shortWhen they get very short

The cell will no longer divideThe cell will no longer divideAlmost like running out of division ticketsAlmost like running out of division tickets

Telomerase is an enzyme that adds telomeresTelomerase is an enzyme that adds telomeresMutations in telomerase gene:Mutations in telomerase gene:

Keeps adding new telomeresKeeps adding new telomeresAllow cancer cells to continually divideAllow cancer cells to continually divideLike counterfeit ticketsLike counterfeit tickets

29

30Causes of Cancer



Prokaryotic chromosome a ring of DNAProkaryotic chromosome a ring of DNAFolded up in an area called the nucleoidFolded up in an area called the nucleoid1,000 X length of cell1,000 X length of cellReplicated into two rings prior to divisionReplicated into two rings prior to divisionReplicate rings attach to plasma membraneReplicate rings attach to plasma membrane

Binary fissionBinary fissionSplitting in two between the two replicate Splitting in two between the two replicate chromosomeschromosomes

Produces two daughter cells identical to Produces two daughter cells identical to original cell – Asexual Reproduction original cell – Asexual Reproduction

31

32Binary Fission of Prokaryotes

33Functions of Cell Division


ReviewReview

The Cell CycleThe Cell Cycle InterphaseInterphaseMitotic StageMitotic StageCell Cycle ControlCell Cycle ControlApoptosisApoptosis

Mitosis & CytokinesisMitosis & Cytokinesis


The Cell Cycle & CancerThe Cell Cycle & Cancer


34

The Cell CycleEnding Slide Chapter 09

The Cell Cycle Chapter 09. The Cell Cycle Outline Interphase Mitotic Stage Cell Cycle Control ...

Documents

Transcript of The Cell Cycle Chapter 09. The Cell Cycle Outline Interphase Mitotic Stage Cell Cycle Control ...