Chromosomes, Mitosis and Chromosomes, Mitosis and MeiosisMeiosis

Chapter 10 Chapter 10

Learning Objective 1Learning Objective 1

• What is the significance of What is the significance of chromosomeschromosomes in terms of information?in terms of information?

ChromosomesChromosomes

OrganizationOrganization

• GenesGenes• cell’s informational unitscell’s informational units• made of DNA made of DNA

• ChromatinChromatin • DNA and proteinDNA and protein• makes up chromosomes (eukaryotes)makes up chromosomes (eukaryotes)

• ChromosomesChromosomes• allow DNA sortingallow DNA sorting• into daughter cellsinto daughter cells

KEY CONCEPTSKEY CONCEPTS

• In eukaryotic cells, DNA is wound around In eukaryotic cells, DNA is wound around specific proteins to form specific proteins to form chromatinchromatin, which , which in turn is folded and packaged to make in turn is folded and packaged to make individual individual chromosomeschromosomes

Learning ObjectiveLearning Objective 22

• How is DNA organized in How is DNA organized in prokaryoticprokaryotic and and eukaryoticeukaryotic cells? cells?

Prokaryotic CellsProkaryotic Cells

• Contain circular DNA moleculesContain circular DNA molecules

Eukaryotic ChromosomesEukaryotic Chromosomes

• NucleosomeNucleosome• histone histone (protein) bead wrapped in DNA(protein) bead wrapped in DNA• organized into coiled loopsorganized into coiled loops• held together by nonhistone held together by nonhistone scaffolding scaffolding

proteinsproteins

NucleosomesNucleosomes

Fig. 10-2a, p. 213

DNA wound around a cluster of histone molecules

Histone tails

Linker DNA

Nucleosome (10 nm diameter)

Fig. 10-2b, p. 213

100 nm

Scaffolding ProteinsScaffolding Proteins

Fig. 10-3, p. 213

DNA

Scaffolding proteins

2 μm

Chromosome OrganizationChromosome Organization

Fig. 10-4, p. 214

1400 nm

700 nm 300 nm fiber (looped domains)

30 nm chromatin fiber

Condensed chromosome

DNA wound around a cluster of histone molecules

Scaffolding proteinCondensed

chromatin Extended chromatin

Packed nucleosomes

Histone10 nm

2 nm Nucleosomes

DNA double helix

Learning ObjectiveLearning Objective 33

• What are the stages in the eukaryotic What are the stages in the eukaryotic cell cell cyclecycle, and their principal events?, and their principal events?

Eukaryotic Eukaryotic Cell CycleCell Cycle

• Cycle of cell divisionCycle of cell division• interphaseinterphase• M phaseM phase

Fig. 10-5, p. 215

INTERPHASE

G1 (First gap phase)

S (Synthesis phase)

G2 (Second gap

phase)

M PHASE (Mitosis and cytokinesis)

InterphaseInterphase

• First gap phase (First gap phase (G1 phase)G1 phase)• cell grows and prepares for S phasecell grows and prepares for S phase

• Synthesis phase (Synthesis phase (S phase)S phase)• DNA and chromosome protein synthesisDNA and chromosome protein synthesis• chromosome duplicationchromosome duplication

• Second gap phase (Second gap phase (G2 phaseG2 phase))• protein synthesis increasesprotein synthesis increases• preparation for cell divisionpreparation for cell division

M PhaseM Phase

• MitosisMitosis• nuclear divisionnuclear division• two nuclei identical to parent nucleustwo nuclei identical to parent nucleus

• CytokinesisCytokinesis• cytoplasm dividescytoplasm divides• two daughter cellstwo daughter cells

KEY CONCEPTSKEY CONCEPTS

• Cell divisionCell division is an important part of the is an important part of the cell cell cyclecycle, which consists of the successive , which consists of the successive stages through which a cell passesstages through which a cell passes

Animation: The Cell CycleAnimation: The Cell Cycle

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Learning ObjectiveLearning Objective 44

• What is the structure of a duplicated What is the structure of a duplicated chromosome, including the chromosome, including the sister sister chromatidschromatids, , centromerescentromeres, and , and kinetochoreskinetochores??

A Duplicated ChromosomeA Duplicated Chromosome

• Consists of a pair of Consists of a pair of sister chromatidssister chromatids• containing identical DNA sequencescontaining identical DNA sequences

• CentromereCentromere• constricted regionconstricted region• joins sister chromatidsjoins sister chromatids

• KinetochoreKinetochore• protein to which microtubules bindprotein to which microtubules bind• attached to centromere attached to centromere

Sister ChromatidsSister Chromatids

Fig. 10-7, p. 218

Centromere region

Microtubules

Kinetochore

Sister chromatids

1.0 μm

Learning ObjectiveLearning Objective 55

• What is the process and significance of What is the process and significance of mitosismitosis??

MitosisMitosis

• Preserves chromosome numberPreserves chromosome number• in eukaryotic cell divisionin eukaryotic cell division

• Identical chromosomes are distributed to Identical chromosomes are distributed to each pole of the celleach pole of the cell• nuclear envelopenuclear envelope forms around each set forms around each set

InterphaseInterphase

Fig. 10-6a, p. 216

INTERPHASE PROPHASE PROMETAPHASE

ChromatinNucleolus Sister chromatids

of duplicated chromosome

KinetochoreNucleus

Spindle microtubule

Pieces of nuclear envelope

Nuclear envelope

Plasma membrane

Developing mitotic spindle

Centrioles

ProphaseProphase

• Chromatin condenses into duplicated Chromatin condenses into duplicated chromosomes (pair of sister chromatids)chromosomes (pair of sister chromatids)

• Nuclear envelope begins to disappearNuclear envelope begins to disappear• Mitotic spindleMitotic spindle begins to form begins to form

Mitotic SpindleMitotic Spindle

Fig. 10-9a, p. 219

Metaphase plate (cell’s midplane)

Kinetochore microtubule (spindle microtubule)

Centrioles

Astral microtubules

Pericentriolar material

Polar (non- kinetochore) microtubule

Sister chromatids

Fig. 10-9b, p. 219

10 μm

ProphaseProphase

PrometaphasePrometaphase

• SpindleSpindle microtubules attach to microtubules attach to kinetochoreskinetochores of chromosomes of chromosomes

• Chromosomes begin to move toward cell’s Chromosomes begin to move toward cell’s midplanemidplane

PrometaphasePrometaphase

MetaphaseMetaphase

• Chromosomes align on cell’s midplane Chromosomes align on cell’s midplane ((metaphase plate)metaphase plate)

• Mitotic spindle is completeMitotic spindle is complete• Microtubules attach kinetochores of sister Microtubules attach kinetochores of sister

chromatids to opposite poles of cell chromatids to opposite poles of cell

MetaphaseMetaphase

AnaphaseAnaphase

• Sister chromatids separateSister chromatids separate• move to opposite polesmove to opposite poles

• Each former chromatid is now a Each former chromatid is now a chromosomechromosome

AnaphaseAnaphase

TelophaseTelophase

• Nuclear envelope re-formsNuclear envelope re-forms• Nucleoli appearNucleoli appear• Chromosomes uncoilChromosomes uncoil• Spindle disappearsSpindle disappears• Cytokinesis beginsCytokinesis begins

TelophaseTelophase

Fig. 10-6b, p. 217

METAPHASE ANAPHASE TELOPHASE

25 μ

m

SpindleCleavage furrow

Centriole pair at spindle pole

Reforming nuclear envelopeCell’s midplane

(metaphase plate)

Daughter chromosomes

KEY CONCEPTSKEY CONCEPTS

• In cell division by In cell division by mitosismitosis, duplicated , duplicated chromosomes separate (split apart) and chromosomes separate (split apart) and are evenly distributed into two daughter are evenly distributed into two daughter nucleinuclei

CytokinesisCytokinesis

Fig. 10-10a, p. 220

Cleavage furrow

Actomyosin contractile ring

10 μm

Fig. 10-10b, p. 220

NucleusCell plate forming

Vesicles gather on

cell’s midplane

Small vesicles

fuse, forming larger

vesicles

Eventually one large

vesicle exists

New cell walls (from

vesicle contents)

Plasma membrane

Cell wall

Cell plate forming

New plasma membranes (from vesicle membranes)

5 μm

Learning ObjectiveLearning Objective 66

• How is the cell cycle controlled?How is the cell cycle controlled?

Cell-Cycle ControlCell-Cycle Control

• Cyclin-dependent kinases (Cdks)Cyclin-dependent kinases (Cdks)• protein kinasesprotein kinases that control cell cycle that control cell cycle• active only when bound to active only when bound to cyclinscyclins

• CyclinsCyclins• regulatory proteinsregulatory proteins• levels fluctuate during cell cyclelevels fluctuate during cell cycle

CyclinsCyclins

Fig. 10-12, p. 222

11 Cyclin is synthesized and accumulates.

2 Cdk associates with cyclin, forming a cyclin–Cdk complex, M-Cdk.

Cdk5 G1

S

M-Cdk phosphorylates proteins, activating those that facilitate mitosis and inactivating those that inhibit mitosis.

3

4 An activated enzyme complex recognizes a specific amino acid sequence in cyclin and targets it for destruction. When cyclin is degraded, M-Cdk activity is terminated, and the cells formed by mitosis enter G1.

M G2

Cyclin 5 Cdk is not degraded but is recycled and reused.

2

Degraded cyclin

Cdk4

M-Cdk (triggers M phase)

3

1

2

3

4

5

KEY CONCEPTSKEY CONCEPTS

• An internal genetic program interacts with An internal genetic program interacts with external signals to regulate the external signals to regulate the cell cyclecell cycle

Learning ObjectiveLearning Objective 77

• What is the difference between What is the difference between asexualasexual and and sexualsexual reproduction? reproduction?

Asexual ReproductionAsexual Reproduction

• Single parent Single parent • offspring have identical hereditary traitsoffspring have identical hereditary traits

• MitosisMitosis• basis for eukaryotic asexual reproductionbasis for eukaryotic asexual reproduction

Binary Binary FissionFission

Fig. 10-11, p. 221

Prokaryotic cellPlasma membrane

1 DNA replication begins at single site on bacterial DNA.Cell wall

Bacterial DNA

Origin of replication

2 Replication continues, as replication enzymes work in both directions from site where replication began.

Two copies of bacterial DNA

3 Replication is completed. Cell begins to divide, as plasma membrane grows inward.

4 Binary fission is complete. Two identical prokaryotic cells result.

Two identical prokaryotic cells

Sexual ReproductionSexual Reproduction

• Two haploid sex cells Two haploid sex cells (gametes)(gametes) fuse to fuse to form a single diploid form a single diploid zygotezygote

• MeiosisMeiosis • produces gametesproduces gametes

Learning ObjectiveLearning Objective 88

• What is the difference between What is the difference between haploidhaploid and and diploiddiploid cells? cells?

• What are What are homologous chromosomeshomologous chromosomes??

DiploidDiploid Cell Cell

• Chromosomes are paired (Chromosomes are paired (homologous homologous chromosomeschromosomes))• similar in length, shape, other featuressimilar in length, shape, other features• carry genes affecting the same traitscarry genes affecting the same traits

HaploidHaploid Cell Cell

• Contains only one member of each Contains only one member of each homologous chromosome pairhomologous chromosome pair

Fig. 10-16, p. 229

Fig. 10-16a, p. 229

MITOSIS

PROPHASE

No synapsis of homologous chromosomes

ANAPHASE

Sister chromatids move to opposite poles

DAUGHTER CELLS

Two 2n cells with unduplicated chromosomes

Fig. 10-16b, p. 229

MEIOSIS

PROPHASE I

Synapsis of homologous chromosomes to form tetrads

ANAPHASE IHomologous chromosomes move to opposite poles

PROPHASE IITwo n cells with duplicated chromosomes

ANAPHASE IISister chromatids move to opposite poles

HAPLOID CELLSFour n cells with unduplicated chromosomes

Learning ObjectiveLearning Objective 99

• What is the process and significance of What is the process and significance of meiosismeiosis??

MeiosisMeiosis

• One One diploiddiploid cell divides two times, yielding cell divides two times, yielding four four haploidhaploid cells cells

• Sexual life cycles in eukaryotes require Sexual life cycles in eukaryotes require meiosismeiosis• each gamete contains half the number of each gamete contains half the number of

chromosomes in parent cellchromosomes in parent cell

Meiosis IMeiosis I

• Prophase IProphase I• homologous chromosomes join homologous chromosomes join (synapsis)(synapsis)

• Crossing-overCrossing-over• between homologous (nonsister) chromatids between homologous (nonsister) chromatids • exchanges segments of DNA strandsexchanges segments of DNA strands

• Results in Results in genetic recombinationgenetic recombination

SynapsisSynapsis

Fig. 10-14a, p. 228

Maternal sister chromatids

Paternal sister chromatids

Synaptonemal complex

ChromatinProtein

Chromatin Maternal sister chromatids

Fig. 10-14b, p. 228

Chromosome

Chromosome

0.5 μm

Synaptonemal complex

Meiosis IMeiosis I

• Metaphase IMetaphase I• tetrads tetrads (homologous chromosomes joined by (homologous chromosomes joined by

chiasmatachiasmata)) line up on metaphase plate line up on metaphase plate

• Anaphase IAnaphase I • homologous chromosomes separate homologous chromosomes separate • distributed to different nucleidistributed to different nuclei

• Each nucleus contains haploid number of Each nucleus contains haploid number of chromosomeschromosomes• each chromosome has 2 chromatidseach chromosome has 2 chromatids

Tetrads and ChiasmataTetrads and Chiasmata

Fig. 10-15a, p. 228

Chiasmata Sister chromatids

Kinetochores

Sister chromatids

1 μm

Fig. 10-15b, p. 228

Sister chromatidsChiasmata

Kinetochores

Meiosis IIMeiosis II

• Two chromatids of each chromosome Two chromatids of each chromosome separateseparate• one distributed to each daughter cell one distributed to each daughter cell

• Each former chromatid is now a Each former chromatid is now a chromosomechromosome

MeiosisMeiosis

MeiosisMeiosis

Fig. 10-13a (1), p. 226

INTERPHASE MEIOSIS I

Mid-prophase I Late prophase I

Nucleolus

Homologous chromosomesChromatin

Developing meiotic spindleCentrioles

Nuclear envelope

Interphase preceding meiosis; DNA replicates.

Homologous chromosomes synapse, forming tetrads; nuclear envelope breaks down.

Fig. 10-13a (2), p. 226

MEIOSIS IIProphase II Metaphase II Anaphase II

Daughter chromosomes

Chromosomes condense again following brief period of interkinesis. DNA does not replicate again.

Chromosomes line up along cell's midplane.

Sister chromatids separate, and chromosomes move to opposite poles.

Fig. 10-13b (1), p. 227

Metaphase I Anaphase I Telophase I

Microtubule attached to kinetochore

Cleavage furrow

Separation of homologous chromosomes

Sister chromatids

Tetrads line up on cell's midplane. Tetrads held together at chiasmata (sites of prior crossing-over).

Homologous chromosomes separate and move to opposite poles. Note that sister chromatids remain attached at their centromeres.

One of each pair of homologous chromosomes is at each pole. Cytokinesis occurs.

Fig. 10-13b (2), p. 227

Telophase II Four haploid cells

25 μm

Nuclei form at opposite poles of each cell. Cytokinesis occurs.

Four gametes (animal) or four spores (plant) are produced.

Learning ObjectiveLearning Objective 1010

• What are the different processes and What are the different processes and outcomes of outcomes of mitosismitosis and and meiosismeiosis? ?

MitosisMitosis

• Single nuclear divisionSingle nuclear division• 2 daughter cells genetically identical to 2 daughter cells genetically identical to

each other and to original celleach other and to original cell• No synapsis of homologous chromosomes No synapsis of homologous chromosomes

MitosisMitosis

MeiosisMeiosis

• Two successive nuclear divisions form Two successive nuclear divisions form four haploid cellsfour haploid cells

• Synapsis of homologous chromosomes Synapsis of homologous chromosomes occurs during prophase Ioccurs during prophase I

MeiosisMeiosis

KEY CONCEPTSKEY CONCEPTS

• MeiosisMeiosis, which reduces the number of , which reduces the number of chromosome sets from chromosome sets from diploiddiploid to to haploidhaploid, , is necessary to maintain the normal is necessary to maintain the normal chromosome number when two cells join chromosome number when two cells join during sexual reproductionduring sexual reproduction

KEY CONCEPTSKEY CONCEPTS

• Meiosis helps to increase Meiosis helps to increase genetic variationgenetic variation among offspringamong offspring

Learning ObjectiveLearning Objective 1111

• Compare the roles of mitosis and meiosis Compare the roles of mitosis and meiosis in various generalized in various generalized life cycleslife cycles

AnimalsAnimals

• Somatic cellsSomatic cells are diploid are diploid• produced by mitosisproduced by mitosis

• GametesGametes are haploid are haploid • produced by meiosis (produced by meiosis (gametogenesis)gametogenesis)

Animal Life CycleAnimal Life Cycle

Fig. 10-17a, p. 230

Gametes (n)

Meiosis Fertilization

Zygote (2n)

Mitosis

Multicellular diploid

organism (2n)

Animals

Simple EukaryotesSimple Eukaryotes

• May be haploidMay be haploid• produced by mitosisproduced by mitosis

• Only diploid stage is the Only diploid stage is the zygotezygote• which undergoes meiosis to restore the which undergoes meiosis to restore the

haploid statehaploid state

Simple Eukaryote Life CycleSimple Eukaryote Life Cycle

Fig. 10-17b, p. 230

Unicellular or multicellular

haploid organism (n)

Mitosis Mitosis

Gametes (n)

Meiosis Fertilization

Zygote (2n)

Simple eukaryotes

PlantsPlants

• Alternation of generationsAlternation of generations::• sporophyte generationsporophyte generation• gametophyte generationgametophyte generation

PlantsPlants

• Sporophyte generationSporophyte generation• multicellular diploid multicellular diploid • forms haploid spores by meiosisforms haploid spores by meiosis

• Spore divides (mitosis) to form Spore divides (mitosis) to form gametophyte generationgametophyte generation• multicellular haploidmulticellular haploid• produces gametes by mitosis produces gametes by mitosis

PlantsPlants

• Two haploid gametes fuse to form diploid Two haploid gametes fuse to form diploid zygotezygote

• ZygoteZygote divides (mitosis) to produce new divides (mitosis) to produce new diploid sporophyte generationdiploid sporophyte generation

Plant Life CyclePlant Life Cycle

Fig. 10-17c, p. 230

Gametophyte (n) (multicellular haploid

organism)

Mitosis Mitosis

Spores (n) Gametes (n)

Meiosis Fertilization

Zygote (2n)

Mitosis

Sporophyte (2n) (multicellular diploid

organism)

Plants, some algae, and some fungi

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