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Mitosis “Nuclear division”: § Dividing cell’s DNA between

2 daughter nucleiu “dance of the chromosomes”

§ 4 phasesu prophaseu metaphaseu anaphaseu telophase

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Prophase: § Chromatin condenses

u visible chromosomes§ chromatids

§ Centrioles move to opposite poles of cell u animal cell

§ Protein fibers cross cell to form mitotic spindleu microtubules

§ actin, myosin u coordinates movement of chromosomes

§ Nucleolus disappears

green = key features

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Transition to Metaphase: § Prometaphase§ Nuclear membrane breaks down

u spindle fibers attach to centromeres§ creating kinetochores

u microtubules attach at kinetochores § connect centromeres to centrioles

u chromosomes begin moving

green = key features

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Metaphase: § Chromosomes align along

middle of cellu metaphase plate

§ meta = middle u spindle fibers coordinate movementu helps to ensure chromosomes

separate properly§ so each new nucleus receives only

1 copy of each chromosome

green = key features

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Anaphase: § Sister chromatids separate at

kinetochores u move to opposite polesu pulled at centromeresu pulled by motor proteins

“walking” along microtubules§ actin, myosin§ increased production of

ATP by mitochondria§ Poles move farther apart

u polar microtubules lengthen

green = key features

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Separation of chromatids:§ In anaphase, proteins holding together sister

chromatids are inactivatedu separate to become individual chromosomes

2 chromosomes1 chromosome2 chromatids single-stranded

double-stranded

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§ Pac-man mechanism: Kinetochores use motor proteins that “walk” chromosome along attached microtubuleu microtubule shortens by

dismantling at kinetochore (chromosome) end

Chromosome movement:2 mechanisms -

§ Reel-in mechanism: microtubules “reel in” to centrioles like a line on a fishing rod

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Telophase:§ Chromosomes arrive at

opposite polesu daughter nuclei formu nucleoli formu chromosomes disperse

§ no longer visible under light microscope

§ Spindle fibers disperse§ Cytokinesis begins

u cell division

green = key features

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Cytokinesis:§ Animals

u constriction belt of actinmicrofilaments around equator of cell§ cleavage furrow forms§ splits cell in two§ like tightening a draw

string

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Cytokinesis in Animals:

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Mitosis in whitefish blastula:

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Mitosis in animal cells:

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Cytokinesis in Plants:§ Plants

u cell plate forms§ vesicles line up at equator

w derived from Golgi§ vesicles fuse to form 2 cell

membranesu new cell wall laid down

between membranes§ new cell wall fuses with

existing cell wall

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Cytokinesis in plant cell:

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Mitosis in plant cell:

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onion root tip

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Origin of replication

chromosome:double-stranded DNA replication

of DNA

elongation of cell

cell pinches in two

ring of proteins

Evolution of mitosis:

§ Mitosis in eukaryotes likely evolved from binary fission in bacteriau single circular

chromosomeu no membrane-bound

organelles

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§ A possible progression of mechanisms intermediate between binary fission & mitosis seen in modern organisms

protistsdinoflagellates

protistsdiatoms

eukaryotesyeast

eukaryotesanimals

prokaryotes(bacteria)Evolution of mitosis:

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Dinoflagellates: § algae

u “red tide”u bioluminescence

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Diatoms: § microscopic algae

u marineu freshwater

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Control of Cell Cycle:

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Kinetochore: § Each chromatid

has own kinetochore proteinsu microtubules

attach to kinetochore proteins

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nucleosomeDNAhistone

DNA double helixchromosome

rosettes ofchromatin loops

scaffoldprotein

chromatin loop

30 nm

Chromosome structure:

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G2

S G1

Mmetaphase

prophaseanaphase

telophase

interphase (G1, S, G2 phases)mitosis (M)cytokinesis (C)

C

§ Phases of a dividing cell’s life u interphase

§ cell grows§ replicates chromosomes§ produces new organelles, enzymes, membranes…§ G1, S, G2

u mitotic phase§ cell separates & divides chromosomes

w mitosis§ cell divides cytoplasm & organelles

w cytokinesis

Cell Division cycle:

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How did you get from there

to here?

1 cell to 100 trillion cells!

And now look at you…