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Mitosis. Mitosis is the process by which new cells are generated. Mitosis produces 2 genetically identical daughter cells. Overview of Mitosis:. Parent cell. Replicated chromosomes condense at the start of mitosis. Mitosis. Sister chromatids separate and two daughter cells are formed.

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Mitosis

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Mitosis

  • Mitosis is the process by which new cells are generated.

  • Mitosis produces 2 genetically identical daughter cells


Overview of Mitosis:

Parent cell

Replicated chromosomescondense at the start of mitosis

Mitosis

Sister chromatids separate and two daughter cells are formed.

Parent cell and daughter cell contain thesame complement of chromosomes.


The cell cycle:


Figure 12.5 The stages of mitotic cell division in an animal cell: G2 phase; prophase; prometaphase


Figure 12.5 The stages of mitotic cell division in an animal cell: metaphase; anaphase; telophase and cytokinesis.


Figure 12.5x Mitosis


How do spindle fibers move the chromosomes?


The kinetochore is a specialized region on the centromere where spindle fibers attach


Motor molecules of the kintochore walk along the microtubule, taking the chromosome with it

As the chromosomes move toward the poles, the microtubules are broken down at the kinetochore end


ATP

ADP+Pi

Motor molecules "walk" along a microtubule track

Transport vesicle

ATP

ADP+Pi

Kinesin

Microtubule


After the nucleus divides, cytokinesis divides the cytoplasm, forming two separate cells


Figure 8.9a

Cytokinesis in animals

Cleavage furrow


Mitosis in a plant cell


Bacteria divide by binary fission


Bacteria divide by binary fission


Bacteria divide by binary fission


Unregulated cell division can lead to cancer

  • Many factors interact with each other to determine whether a cell will undergo mitosis

  • Cell cycle checkpoints normally insure that DNA replication and mitosis occur only when conditions are favorable and the process is working correctly.


Cell-Cycle Checkpoints

G2 checkpoint

Pass this checkpoint if:• cell size is adequate• chromosome replication is successfully completed

M

Mitosis

G2

Second gap

Metaphase checkpoint

Pass this checkpoint if:• all chromosomes are

attached to mitotic spindle

G1

First gap

G1 checkpoint

DNA synthesis

Pass this checkpoint if:• cell size is adequate• nutrient availability is sufficient• growth factors (signals from other cells) are present

S


Cell cycle proteins regulate whether a cell will proceed past a particular cell cycle checkpoint

  • cyclin-  a protein whose amount varies cyclically

  • cdk- another cell division control protein - a cyclin dependent kinase; active only when bound to cyclin

  • MPF- mitotic promoting factor...  

    • MPF is a kinaseenzyme, ones that switches on/off target proteins by phosphorylating them..... 

    • [cyclin + cdk = MPF]...    favors Mitosis

    • leads to destruction of cyclin itself


MPF levels rise, causing the cell to pass through the G2 checkpoint


Growth factor proteins are signal molecules that trigger a signal-transduction pathway leading to cell division

Platelet-derived growth factor


Cell division is also dependent on environmental factors


Unregulated cell division can lead to cancer

  • Mutations in genes that encode cell cycle proteins can lead to unregulated growth, resulting in tumor formation and ultimately invasion of cancerous cells to other organs.


Cancer cells have escaped cell cycle controls and divide excessively


Figure 12-17x1 Breast cancer cell


Figure 12-17x2 Mammogram: normal (left) and cancerous (right)


CANCER SPREADS


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