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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