mitosis

No Bellringer This Week

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Agenda• NOTES: Mitosis

– Details of Chromosome Structure– Organelles Involved in Division– Mnemonic Device for PMATC– Details of each step of Mitosis

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Structure of Chromosomes• Chromosomes are tightly packed bundles

of DNA that look like the letter X.• The left and right halves of chromosomes

are identical strands called “Sister Chromatids”.

• The spot where the chromatids connect together is called the centromere.

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ChromosomChromosomeses

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Nuclear Membrane• The Nuclear Membrane is the outer skin

of the nucleus.• It is the the “Sac” that holds Chromatin.• It is sometimes called the Nuclear

Envelope.

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Cytoskeleton• The cytoskeleton is a network of protein

fibers that run throughout the cell.• These fibers maintain the shape of a cell

and act as tiny muscles to stretch and move.

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BLUE = MicrotubulesGREEN = Intermediate FilamentsRED = Microfilaments

Mitotic Spindle• The mitotic spindle is a collection of fibers

that pull chromosomes apart during mitosis.

• It has 3 major components– Centrioles: A pair of organelles that anchor the

mitotic spindle at opposite ends of the cell.– Asters: Short fibers that radiate out from the

centrioles in order to hold their position– Kinetechore fibers: Long fibers that pull

chromosomes apart and toward either end of cell.

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Steps of Mitosis• Mitosis is the division of Eukaryotic

Cells.• It has 5 steps

– Prophase– Metaphase– Anaphase– Telophase– Cytokinesis

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Pass Me Another Tasty Cupcake

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Pimps Make All That Cash

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Pet My Alligator, Tom Cruise

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P.M.A.T.C.

• Pass Me Another Tasty Cupcake

• Pimps Make All That Cash

• Pet My Alligator, Tom Cruise

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Prophase• Chromatin in the DNA coils to make

chromosomes• The nuclear membrane breaks down,

releasing chromosomes into the cytoplasm

• Centrioles move to opposite ends of the cell and the mitotic spindle forms between them.

• Kinetechore fibers from each half of the spindle attach to the centromere region of each chromosome.

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Metaphase• Kinetechore fibers of the spindle move

chromosomes towards center of the cell.

• By the end of this phase all chromosomes are lined up along the “equator”.

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MetaphaseMetaphase

ChromosoChromosomes lined mes lined at the at the EquatorEquator

Asters at Asters at the polesthe poles

Spindle Spindle FibersFibers

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Anaphase• Chromosomes are split apart and Sister

chromatids are pulled in opposite directions

• This occurs very quickly (Less than 5 minutes)

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AnaphaseAnaphase

Sister Sister ChromatidChromatid

s being s being separatedseparated

Telophase• Sister chromatids arrive at opposite ends

of the cell and begin converting back into chromatin.

• A nuclear envelope forms around each set of DNA to create new nuclei.

• The mitotic spindle is broken down.

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Cytokinesis• The Cell Membrane pinches together

between the 2 newly formed nuclei• This movement is done by the

cytoskeleton.

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BrainPOP: Mitosis

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Assignment• 17 review questions• Due Tomorrow

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