MITOSIS

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MITOSIS
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MITOSIS

• Primary purpose is to increase the number of
  cells
• Daughter cells are genetically identical to the
  parents
• Occurs during growth and asexual reproduction.
• Mitosis is a continuous process which is divided
  for convenience into a number of stages.

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MITOSIS

• Interphase
• Sometimes called the resting stage between
  divisions
• BUT cells are metabolically very active
• The amount of DNA in the nucleus doubles
• New organelles such as mitochondria are made.

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MITOSIS

• Interphase
• No chromosomes are visible
• The chromosome material, chromatin, is spread
  through the nucleus in a diffuse form.

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MITOSIS

• Prophase
• The longest stage
• Chromosomes become visible
• In animal cells, the centrioles divide and move
  to opposite ends of the nucleus

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MITOSIS

• Prophase
• Protein microtubules develop from each centriole
  forming spindle fibres.
• (In plant cells there are no centrioles and the
  spindle forms independently)

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MITOSIS

• Prophase
• Towards the end of prophase each chromosome can
  be seen to consist of two chromatids held
  together by a centromere.

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MITOSIS

• Prophase
• At the end of prophase the nucleolus disappears
  and the nuclear envelope breaks down.

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MITOSIS

• Metaphase
• Chromosomes line up on the equator of the
  spindle.
• They attach themselves to the spindle by their
  centromere

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MITOSIS

• Anaphase
• The centromeres divide
• The free chromatids move to the poles

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MITOSIS

• Anaphase
• This movement results from the contraction of the
  spindle fibres.
• As they shorten they pull the chromatids apart.

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MITOSIS

• Telophase
• The chromatids have reached the poles and are now
  regarded as distinct chromosomes again.
• A nuclear envelope forms around each group of
  chromosomes

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MITOSIS

• Telophase
• The chromosomes uncoil returning to chromatin
• The cytoplasm divides by cytokinesis.

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CYTOKINESIS

• Animal cells
• The centre of the cell pinches in to form a
  division furrow.
• As the division deepens, the cell surface
  membrane on each side joins up.
• Two separate cells result.

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CYTOKINESIS

• Plant cells
• Vesicles produced by the Golgi body collect on
  equator of cell
• These vesicles fuse to form a cell plate.
• The cell plate eventually stretches right across
  the cell forming the middle lamella.
• Cellulose builds up on lamella to form cell walls.

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CYTOKINESIS