Mitosis

The five processes of mitosis and the importance of mitosis

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  • Created by: Dalia
  • Created on: 23-03-13 11:31

Interphase

  • Cell is actively synthesising proteins
  • Chromosomes invisible
  • Occupies most of the cell cycle
  • Known as the resting phase because no division takes place
  • Divided into three parts
    • First growth (G1) phase, when the proteins from which cell organelles are synthesised are produced
    • Synthesis (S) phase, when DNA is replicated 
    • Second growth (G2) phase, when organelles grow and divide and energy stores are increased
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Prophase

  • Chromosomes become visible
  • Nuclear envelope disappears
  • Nucleolus disappears
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Metaphase

  • Chromosomes arrange themselves at the centre of the cell
  • Spindle forms
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Anaphase

  • Each of the two threads of a chromosome (chromatid) migrates to an opposite pole
  • Spindle fibres attached to the chromatids contract
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Telophase

  • Nuclear envelope reforms
  • Chromatids reach poles and become indistinct
  • Nucleolus reforms
  • Spindle disintegrates
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Importance of Mitosis: Growth

  • When two haploid cells (e.g. a sperm and an ovum) fuse together to form a diploid cell, this diploid cell has all the genetic information needed to form a new organism.
  • If the new organism is to resemble its parents, all the cells that grow from this original cell must possess the same set of genetic information.
  • Mitosis ensures that this happens.
  • The cell firstly divides to give a group of identical cells.
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Importance of Mitosis: Differentiation

  • These cells change, or differentiate, to give groups of specialised cells, e.g. epithelium in animals or xylem in plants.
  • These different cell types each divide by mitosis to give tissues made up of identical cells which perform a particular function.
  • This is essential as the tissue can only function efficiently if all its cells have the same structure and perform the same function.
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Importance of Mitosis: Repair

  • If cells are damaged or die, it is important that the new cells produced have an identical structure and function to the ones that have been lost.
  • If they were not exact copies then the tissue would not function as effectively as before.
  • Mitosis is therefore the means by which new cells replace dead or damaged ones.
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Cancer

  • Cancer is a group of diseases caused by a growth disorder in cells.
  • It is the result of damage to the genes that regulate mitosis and the cell cycle.
  • This leads to uncontrolled growth of cells.
  • As a consequence, a group of abnormal cells, called a tumour, develops and constantly expands in size.
  • Cancers can develop in any organ of the body.
  • Drugs used to treat cancer (chemotherapy) disrupt the cell cycle by:
    • preventing DNA from replicating, e.g. cisplatin
    • inhibiting the metaphase stage of mitosis by interfering with spindle formation, e.g. vinca alkanoids
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