Mitosis and Cytokinesis

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Mitosis and Cytokinesis

• Section 6-3

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In Mitosis, Chromatids are pulled by Microtubules

• During mitosis the nucleus divides to form two
  nuclei, each containing a complete set of
  chromosomes and the chromatids on each chromosome
  are physically moved to opposite sides of the
  dividing cell with the help of the spindle.
• During cytokinesis the cytoplasm is divided
  between the two resulting cells.

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• Spindles cell structures made up of both
  centrioles and individual microtubule fibers that
  are involved in moving chromosomes during cell
  division.
• Forming the Spindles in Animal Cells
• 1. One pair of centrioles, at right angles to
  one another
• 2. During G2 phase the centriole pair is
  replicated so that the cell has two pairs of
  centrioles as it enters the mitotic phase.

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• 3. When the cell enters mitotic phase, centriole
  pairs begin to separate, moving towards the
  opposite poles of the cell.
• 4. As centrioles separate, spindles begin to
  form.
• 5. Centrioles and spindle fibers both made of
  hollow tubes of protein called microtubules.

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• Each spindle fiber made of an individual
  microtubule. Each centriole, however, is made of
  nine triplets of microtubules arranged in a
  circle.
• Forming Spindle Fibers in Plant Cells
• Plant cells do not have centrioles, but they form
  a spindle almost identical to that of an animal
  cell.

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The Mitotic Spindle
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Separating Chromatids by Attaching Spindle Fibers

• Some microtubules in spindle interact with each
  other, others attach to a protein structure found
  on each side of the centromere.
• The two sets of microtubules extend out toward
  opposite poles of the cell.

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• Once microtubules attach to centromeres and
  poles, chromatids can be separated.
• Chromatids moved to each pole of cell in a manner
  similar to bringing in a fish with a fishing
  pole. When microtubule is reeled in, the
  chromatids are dragged to opposite poles.
• Reeling occurs because ends of spindle fibers are
  broken down bit by bit at each of the poles.
  Fibers become shorter chromatids move closer.

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• As soon as chromatids separate from each other
  called chromosomes.
• When finally arrive at the poles, one complete
  set is present.

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Mitosis and Cytokinesis Divide Cells

• Mitosis - Continuous process, but divided into
  four stages
• P Prophase
• M Metaphase
• A Anaphase
• T Telophase

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Stage One Prophase

• Chromosomes coil up and become visible
• Nuclear envelope dissolves
• Spindle forms

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Stage Two Metaphase

• chromosomes move to center of cell and line up
  along the equator
• spindle fibers link chromatids to opposite poles

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Stage Three Anaphase

• centromeres divide
• two chromatids (now called chromosomes) move
  toward opposite poles of cell as spindle fibers
  shorten

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Stage Four Telophase

• nuclear envelope forms around chromosomes at
  opposite pole of cell
• chromosomes uncoil
• spindle dissolves

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• After four stages are complete, so is mitosis.

http//www.biology.arizona.edu/Cell_bio/tutorials/
cell_cycle/cells3.html http//www.johnkyrk.com/mi
tosis.html http//www.accessexcellence.org/RC/VL/
GG/mitosis.html http//www.cellsalive.com/mitosis
.htm
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Cytokinesis

• Begins as mitosis ends
• cytoplasm of cell is divided in half
• cell membrane grows to enclose each cell, which
  forms two cells
• end result of mitosis and cytokinesis two
  identical cells

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• Animal cells and other cells without cell walls
  cell is pinched in half by a belt of protein
  threads
• Plant cells and other cells with cell walls have
  a different method of dividing cytoplasm.
• vesicles formed by the Golgi apparatus fuse at
  midline of dividing cell and form a cell plate
• Cell Plate membrane bound cell wall that forms
  across the middle of a plant cell in cytokinesis

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• New cell wall forms on both sides of the cell
  plate.
• When complete cell plate separates plant cell
  into two new plant cells.

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• In plant and animal cells, offspring cells are
  about the same size. Each has an identical copy
  of the original cells chromosomes and about ½ of
  the cytoplasm and organelles.

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Summary

• Before mitosis begins, the cell will form the
  mitotic spindle during the G2 phase of the cell
  cycle.
• Mitosis occurs in four stages PMAT
• Cytokinesis occurs after mitosis division of
  the cells cytoplasm
• http//school.discoveryeducation.com/quizzes6/musk
  opf/mitosis1.html

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HOMEWORK

• Section 6-3 Review Questions
• Math Lab p. 129