Cellular DivisionCellular Division

2

Binary FissionBinary Fission

DNA replicated

Membrane added

3

Cell DivisionCell Division

Functions in Reproduction, Growth, and RepairFunctions in Reproduction, Growth, and Repair• Unicellular OrganismsUnicellular Organisms

• Reproduction of Entire OrganismsReproduction of Entire Organisms• Multicellular OrganismsMulticellular Organisms

• Growth and Development from the Fertilized EggGrowth and Development from the Fertilized Egg• Replacement of Damaged or Dead CellsReplacement of Damaged or Dead Cells

• Distributes Identical Sets of ChromosomesDistributes Identical Sets of Chromosomes• Precisely Replicates its DNAPrecisely Replicates its DNA• Results in 2 Daughter CellsResults in 2 Daughter Cells

4Binary Fission in Bacterium:Binary Fission in Bacterium:Asexual Reproduction by MitosisAsexual Reproduction by Mitosis

Division planeDivision plane

Cell wallCell wall

CytoplasmCytoplasm

NuclearNuclearmaterialmaterial

5Binary Fission in Paramecium:Binary Fission in Paramecium:Asexual Reproduction by MitosisAsexual Reproduction by Mitosis

New individualsNew individuals

6Budding Yeast:Budding Yeast:Asexual Reproduction by MitosisAsexual Reproduction by Mitosis

Nucleus divides by Nucleus divides by mitosis.mitosis.

Bud forms on cell.Bud forms on cell.Nucleus moves into Nucleus moves into

bud.bud.Bud separates.Bud separates.

7Budding Hydra:Budding Hydra:Asexual Reproduction by MitosisAsexual Reproduction by Mitosis

8

Mitotic Mitotic

cell cell divisiondivision

Mitotic Mitotic cell cell division & division &

differ-differ-entiationentiation

Growth and Development:Growth and Development:Functions of MitosisFunctions of Mitosis

TissuesTissues

OrgansOrgansFertilized eggFertilized egg(zygote)(zygote) Multicell stageMulticell stage

9

telophase

metaphase

anaphase

cell

divi

sion

GG00: nondividing: nondividing

interphaseinterphase

The EukaryoticThe EukaryoticCell CycleCell Cycle

S: Synthesis S: Synthesis of DNA; of DNA; chromosomes chromosomes duplicatedduplicated

GG11: Growth: Growth

GG22: Growth: Growth

prophase

cytokinesis

Mito

sis

10

The Cell CycleThe Cell Cycle

Alternates between mitotic (M) phase and Alternates between mitotic (M) phase and interphase in eukaryotes.interphase in eukaryotes.

InterphaseInterphase– ~90% of cycle~90% of cycle– chromosome replicationchromosome replication– cell growth and metabolismcell growth and metabolism– three periodsthree periods

1.1. G1 phase – first growth phaseG1 phase – first growth phase2.2. S phase – synthesis of duplicated DNAS phase – synthesis of duplicated DNA3.3. G2 phase – second growth phaseG2 phase – second growth phase

11

Interphase : The chromosomes (blue) are in the thin, extended state and appear as a mass in the center of the cell. The microtubules (red) extend outward from the nucleus to all parts of the cell.

Interphase (nondividing)Interphase (nondividing)

12

Interphase : The chromosomes (blue) are in the thin, extended state and appear as a mass in the center of the cell. The microtubules (red) extend outward from the nucleus to all parts of the cell.

Late prophase: Chromosomes have condensed and attached to microtubules. Microtubules have reorganized to form the spindle. Chromatid develops a kinetechore.

Phases of Mitosis (nuclear division): Phases of Mitosis (nuclear division): ProphaseProphase

13

11 single-stranded chromosomesingle-stranded chromosome22 double helixdouble helix

uncondenseduncondensed

DNA replicationDNA replication

11 double-stranded chromosomedouble-stranded chromosome22 double helicesdouble helices

still uncondensedstill uncondensed

Chromosome Chromosome condensationcondensation

11 double-stranded chromosomedouble-stranded chromosome22 double helicesdouble helices

now condensednow condensed

centromere centromere aachromatidchromatid

cellcell basebasepairspairs

closer lookstill closer lookeven closer look

Chromosome CondensationChromosome Condensation

14HumanHumanChromosomes during MitosisChromosomes during Mitosis

15

Human Karyotype, MaleHuman Karyotype, Male

These are These are chromosomes from chromosomes from mitosismitosis

Stained to show Stained to show regionsregions

Numbered by lengthNumbered by lengthOccur in pairsOccur in pairs

16

Interphase : The chromosomes (blue) are in the thin, extended state and appear as a mass in the center of the cell. The microtubules (red) extend outward from the nucleus to all parts of the cell.

Metaphase: The chromosomes have moved along the spindle microtubules to the equator of the cell. Centromeres align on the equator. Entire structure of microtubules is called the spindle.

Late prophase: Chromosomes have condensed and attached to microtubules. Microtubules have reorganized to form the spindle. Chromatid develops a kinetechore.

Phases of Mitosis (nuclear division):Phases of Mitosis (nuclear division):MetaphaseMetaphase

17

Separation of Sister ChromatidsSeparation of Sister Chromatids

In metaphase, sister chromatids In metaphase, sister chromatids are held together at centromereare held together at centromere

At end of metaphase, centromere At end of metaphase, centromere releases sister chromatidsreleases sister chromatids

In anaphase, they move to opposite In anaphase, they move to opposite polespoles

In metaphase, sister chromatids In metaphase, sister chromatids are held together at centromereare held together at centromere

At end of metaphase, centromere At end of metaphase, centromere releases sister chromatidsreleases sister chromatids

In anaphase, they move to opposite In anaphase, they move to opposite polespoles

18

Anaphase: Sister chromatids have separated into separate chromosomes. Kineteochore microtubules shorten at kinetochore. Poles move farther apart.

Telophase: Nonkinetochore microtubules elongate cell. The chromosomes have gathered into two clusters, one at the site of each future nucleus.

Next interphase: Chromosomes are relaxing again into their extended state. Spindle fibers are disappearing, and the microtubules of the 2 daughter cells rearrange into the interphase pattern.

Phases of Mitosis:Phases of Mitosis:Anaphase & TelophaseAnaphase & Telophase

19Mitosis:Mitosis:Prophase - MetaphaseProphase - Metaphase

Kinetochores align at cell’s

equator

Nucleolus disappears;

Nuclear envelope breaks down

Microtubules attach to

kinetochores

Chromosomes condense and

shorten

Centrioles begin to move apart;Spindle forms

Duplicated chromosomes

remain elongated

Centrioles have also been duplicated

LateLateInterphaseInterphase

EarlyEarlyProphaseProphase

LateLateProphaseProphase MetaphaseMetaphase

20MitosisMitosisAnaphase - CytokinesisAnaphase - Cytokinesis

Free spindle fibers push poles apart

Chromatids become

independent chromosomes

One set of chromosomes;

Begin unwinding

Nuclear envelope re-

forms

Cytoplasm divided along

equator

Each daughter gets 1 nucleus &

half of cytoplasm

Spindle disappears; Nucleolus reappears

AnaphaseAnaphase TelophaseTelophase CytokinesisCytokinesisNextNext

InterphaseInterphase

21

Cytokinesis of a Ciliated CellCytokinesis of a Ciliated Cell

Cleavage FurrowCleavage Furrow

Daughter CellsDaughter Cells

22

Cytokinesis in PlantsCytokinesis in Plants

Vesicles fuse to form cell wall

and membranesComplete

separation of daughter cells

23Mitosis, Meiosis,Mitosis, Meiosis,and the Sexual Cycleand the Sexual Cycle

24

Meiosis IMeiosis IHomologous

chromosomes pair and cross over

Homologous chromosomes

exchange DNA & align on equator

Homologous chromosomes move to

opposite poles

Prophase IProphase I Metaphase IMetaphase I Anaphase IAnaphase I Telophase ITelophase I

25

Meiosis IIMeiosis II

Prophase IIProphase II Metaphase IIMetaphase II Anaphase IIAnaphase II Telophase IITelophase IIFourFour

HaploidHaploidCellsCells

Similar to MitosisSimilar to Mitosis

26

Crossing OverCrossing Over

Homologues Homologues pair uppair up

Protein strands Protein strands zip togetherzip together

Recombination Recombination enzymes snip enzymes snip and rejoin and rejoin DNADNA

Homologs Homologs separate with separate with new gene new gene combinationscombinations

27Meiosis vs. Mitosis:Meiosis vs. Mitosis:Comparison of SpindlesComparison of Spindles

Meiosis: Duplicated chromosomes Meiosis: Duplicated chromosomes with one kinetochore; Paired with one kinetochore; Paired homologues go to opposite poles.homologues go to opposite poles.

Meiosis: Duplicated chromosomes Meiosis: Duplicated chromosomes with one kinetochore; Paired with one kinetochore; Paired homologues go to opposite poles.homologues go to opposite poles.

Mitosis: Duplicated chromosomes Mitosis: Duplicated chromosomes with two kinetochores; Unpaired with two kinetochores; Unpaired homologs split between sister homologs split between sister chromatids, which go to opposite chromatids, which go to opposite poles.poles.

Mitosis: Duplicated chromosomes Mitosis: Duplicated chromosomes with two kinetochores; Unpaired with two kinetochores; Unpaired homologs split between sister homologs split between sister chromatids, which go to opposite chromatids, which go to opposite poles.poles.

28Meiosis vs. Mitosis:Meiosis vs. Mitosis:Comparison of StagesComparison of Stages

29

Metaphase Alignment ScenariosMetaphase Alignment Scenarios

The endThe end