Mitosis

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Mitosis is the process of nuclear division that produces two identical daughter cells with a diploid complement of chromosomes from the parent cell. [[Cytokinesis|Cytokinesis usually]] occurs with [[Mitosis|mitosis]], this is the process where the cell itself divides in order to yield two daughter cells. Mitosis only occurs in somatic tissues which are ordinary body cells, such as, liver cells, skin cells, etc<ref>Hartl, D. Ruvolo, M. (2012) Genetics. Burlington: Jones and; Bartlett learning. pg 119, 120</ref>. In multicellular [[Eukaryotic|eukaryotic cells]] mitosis is a way for cells to repairing tissues, to accommodate for growing organisms, embryonic development, production of reticulocytes and to form identical cells to replace dying cells. In unicellular eukaryotic organisms, for example, yeast, mitosis is a way to reproduce asexually<ref>Hartl, D. Ruvolo, M. (2012) Genetics. Burlington: Jones and; Bartlett learning. ph 119, 120</ref>. Check it out on The Mitosis Cycle on YouTube. It can be broken down into four main stages seen in animal cells:  
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Mitosis is the process of nuclear division that produces two identical daughter cells with a diploid complement of [[Chromosomes|chromosomes]] from the parent cell. [[Cytokinesis|Cytokinesis usually]] occurs with [[Mitosis|mitosis]], this is the process where the cell itself divides in order to yield two daughter cells. Mitosis only occurs in somatic tissues which are ordinary body cells, such as, liver cells, skin cells, etc<ref>Hartl, D. Ruvolo, M. (2012) Genetics. Burlington: Jones and; Bartlett learning. pg 119, 120</ref>. In multicellular [[Eukaryotic|eukaryotic cells]] mitosis is a way for cells to repairing tissues, to accommodate for growing organisms, embryonic development, production of [[Reticulocyte|reticulocytes]] and to form identical cells to replace dying cells. In unicellular eukaryotic organisms, for example, yeast, mitosis is a way to [[Asexual_reproduction|reproduce asexually]]<ref>Hartl, D. Ruvolo, M. (2012) Genetics. Burlington: Jones and; Bartlett learning. ph 119, 120</ref>. Check it out on The Mitosis Cycle on YouTube. It can be broken down into four main stages seen in animal cells:  
  
 
=== [[Interphase|Interphase]]  ===
 
=== [[Interphase|Interphase]]  ===
  
If a cell is not undergoing mitotic cell division, the cell is in interphase. In this phase, the chromosomes are invisible through a light microscope<ref>Hartl, D. Ruvolo, M. (2012) Genetics. Burlington: Jones and Bartlett learning. pg 119, 120</ref>.
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If a cell is not undergoing mitotic cell division, the cell is in interphase. In this phase, the chromosomes are invisible through a [[Light_microscope|light microscope]]<ref>Hartl, D. Ruvolo, M. (2012) Genetics. Burlington: Jones and Bartlett learning. pg 119, 120</ref>.  
  
 
Interphase constitutes for most of the [[Cell cycle|cell cycle]];  
 
Interphase constitutes for most of the [[Cell cycle|cell cycle]];  
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During Gap phase 1 biosynthetic activity in the cell is increased as the cell grows and replicates it's [[Organelles|organelles]] whilst producing spare [[Proteins|proteins.]]  
 
During Gap phase 1 biosynthetic activity in the cell is increased as the cell grows and replicates it's [[Organelles|organelles]] whilst producing spare [[Proteins|proteins.]]  
  
During S phase the cell must replicate its DNA, in order for the two daughter cells produced via the following division to have a complete set of genetic material. [[Chromosome|Chromosomes]] are duplicated during this same phase, this produces 2 sister chromatids, allowing each daughter cell which results from the mitotic division to have the diploid number of chromosomes.  
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During S phase the cell must replicate its DNA, in order for the two daughter cells produced via the following division to have a complete set of genetic material. [[Chromosome|Chromosomes]] are duplicated during this same phase, this produces 2 sister [[Chromatids|chromatids]], allowing each daughter cell which results from the mitotic division to have the diploid number of chromosomes.  
  
 
During Gap phase 2 the cell continues to grow and it produces specific proteins necessary for cell division so that mitosis can follow interphase.  
 
During Gap phase 2 the cell continues to grow and it produces specific proteins necessary for cell division so that mitosis can follow interphase.  
  
Another vital event which occurs during interphase is that the cell repairs any DNA damage, to ensure that no undesirable [[Mutations|mutations]] are passed on to the progeny cells<ref>AS-Level Biology-The revision guide.Cumbria: Coordination group publications Ltd. 2. Hartl, D.L. and Ruvolo, M,2011.Genetics-analysis of genes and genomes.8th ed.Burlington MA: Jones and Bartlett Learning.</ref>.
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Another vital event which occurs during interphase is that the cell repairs any DNA damage, to ensure that no undesirable [[Mutations|mutations]] are passed on to the progeny cells<ref>AS-Level Biology-The revision guide.Cumbria: Coordination group publications Ltd. 2. Hartl, D.L. and Ruvolo, M,2011.Genetics-analysis of genes and genomes.8th ed.Burlington MA: Jones and Bartlett Learning.</ref>.  
  
=== [[Prophase|Prophase]] ===
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=== [[Prophase|Prophase]] ===
  
During interphase, the chromosomes are already doubled, this has two closely associated subunits called chromatids. Each pair of chromatids is a product from duplication of one chromosome in the S phase from interphase. These chromatids are held together by the centromere<ref>Johnson, A. et al. (2008) The Cell. 5th edn. Abingdon: Garlan Science. pg 1071, 1072, 1073.</ref>. Throughout the process of prophase the [[Chromosome|chromosomes]] condense meaning they get shorten and thicken to form visibly distinct threads within the [[Nucleus|nucleus]]. This is brought about by the action of large proteins called [[Condensins|condensins]]. Each </span>[[Chromosome|chromosome]] at this point consists of two </span>[[Chromatids|chromatids]] held together at the </span>[[Centromere|centromere]]<span style="line-height: 1.5em"> (central point). Meanwhile, outside the nucleus, the mitotic spindles assemble this is between the two centrioles. The centrioles have replicated and moved apart in order to do this. </span>  
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During interphase, the chromosomes are already doubled, this has two closely associated subunits called chromatids. Each pair of chromatids is a product from duplication of one chromosome in the S phase from interphase. These chromatids are held together by the [[Centromere|centromere]]<ref>Johnson, A. et al. (2008) The Cell. 5th edn. Abingdon: Garlan Science. pg 1071, 1072, 1073.</ref>. Throughout the process of prophase the [[Chromosome|chromosomes]] condense meaning they get shorten and thicken to form visibly distinct threads within the [[Nucleus|nucleus]]. This is brought about by the action of large proteins called [[Condensins|condensins]]. Each &lt;/span&gt;[[Chromosome|chromosome]] at this point consists of two &lt;/span&gt;[[Chromatids|chromatids]] held together at the &lt;/span&gt;[[Centromere|centromere]]<span style="line-height: 1.5em"> (central point). Meanwhile, outside the nucleus, the mitotic spindles assemble this is between the two centrioles. The centrioles have replicated and moved apart in order to do this. </span>  
  
 
=== [[Prometaphase|'''Prometaphase''' ]]  ===
 
=== [[Prometaphase|'''Prometaphase''' ]]  ===
  
The beginning of prometaphase includes the breakdown of the nuclear envelope, this, therefore, means the spindle microtubules from the centrioles can attach to the centromere of the chromosomes. This is by kinetochores which then undergo active movement. The centrioles are at opposite poles when this stage begins. During this phase chromosomes are recognisable as double structures<ref>Johnson, A. et al. (2008) The Cell. 5th edn. Abingdon: Garlan Science. pg 1071, 1072, 1073.</ref>.
+
The beginning of prometaphase includes the breakdown of the nuclear envelope, this, therefore, means the spindle microtubules from the centrioles can attach to the centromere of the chromosomes. This is by [[Kinetochores|kinetochores]] which then undergo active movement. The centrioles are at opposite poles when this stage begins. During this phase chromosomes are recognisable as double structures<ref>Johnson, A. et al. (2008) The Cell. 5th edn. Abingdon: Garlan Science. pg 1071, 1072, 1073.</ref>.  
  
[[Image:MITOSIS.gif|right|The four phases of mitosis.]]
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[[Image:MITOSIS.gif|right|The four phases of mitosis.]]  
  
=== [[Metaphase|Metaphase]] ===
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=== [[Metaphase|Metaphase]] ===
  
 
The mitotic spindle consisting of [[Microtubules|microtubules]] formed by the polymerization of [[Tubulin|tubulin]] begins to form. There are three types of microtubule in the spindle:  
 
The mitotic spindle consisting of [[Microtubules|microtubules]] formed by the polymerization of [[Tubulin|tubulin]] begins to form. There are three types of microtubule in the spindle:  
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NB. [[Centrosomes|Centrosomes]] are located at the ends/poles of the spindle and are microtubule organising centres where [[Tubulin|tubulin]] polymerisation is initiated. These Centrosomes are formed by duplication of one centrosome during interphase.  
 
NB. [[Centrosomes|Centrosomes]] are located at the ends/poles of the spindle and are microtubule organising centres where [[Tubulin|tubulin]] polymerisation is initiated. These Centrosomes are formed by duplication of one centrosome during interphase.  
  
The microtubules form when new tubulin subunits are added to the growing end. However, this can become unstable and the process of depolymerization can be initiated causing the polymer to shrink. This process is regulated by a number of proteins that maintain a balance between polymerization and depolymerization<ref>Hartl, D. Ruvolo, M. (2012)Genetic: analysis of Genes and Genomes 8th edition jones and bartlett learning USA</ref>.  
+
The microtubules form when new tubulin subunits are added to the growing end. However, this can become unstable and the process of depolymerization can be initiated causing the polymer to shrink. This process is regulated by a number of proteins that maintain a balance between [[Polymerisation|polymerization]] and depolymerization<ref>Hartl, D. Ruvolo, M. (2012)Genetic: analysis of Genes and Genomes 8th edition jones and bartlett learning USA</ref>.  
  
 
The next step in metaphase is the formation of the [[Kinetochore|kinetochore]], a site of attachment between the [[Chromosome|chromosome]] and the [[Spindle|spindle]] microtubules<ref>http://www.ncbi.nlm.nih.gov/pubmed/16214339</ref>. Only [[Chromosomal microtubules|chromosomal microtubules]] that make contact with the [[Kinetochore|kinetochore]] however, will become stabilised and others will depolymerise.  
 
The next step in metaphase is the formation of the [[Kinetochore|kinetochore]], a site of attachment between the [[Chromosome|chromosome]] and the [[Spindle|spindle]] microtubules<ref>http://www.ncbi.nlm.nih.gov/pubmed/16214339</ref>. Only [[Chromosomal microtubules|chromosomal microtubules]] that make contact with the [[Kinetochore|kinetochore]] however, will become stabilised and others will depolymerise.  
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The final part involves a position near to the centre of the [[Cell|cell]], known as the [[Metaphase plate|metaphase plate]]. The kinetochore signals for each [[Chromosome|chromosome]] to move to the plate via [[Dephosphorylation|dephosphorylation]] of certain proteins. The [[Cell|cell]] can then only move on to anaphase when all kinetochores are under tension and are aligned on the metaphase plate.  
 
The final part involves a position near to the centre of the [[Cell|cell]], known as the [[Metaphase plate|metaphase plate]]. The kinetochore signals for each [[Chromosome|chromosome]] to move to the plate via [[Dephosphorylation|dephosphorylation]] of certain proteins. The [[Cell|cell]] can then only move on to anaphase when all kinetochores are under tension and are aligned on the metaphase plate.  
  
=== [[Anaphase|Anaphase]] ===
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=== [[Anaphase|Anaphase]] ===
  
[[Proteins|Proteins]] holding the [[Chromatids|chromatids]] together dissolve and [[Centromeres|centromeres]] separate (This is also known as [[Disjunction|disjunction]]). The [[Kinetochore]] microtubules begin to get shorter and shorter, at the same time the spindle fibres also get shorter and therefore move apart<ref>Johnson, A. et al. (2008) The Cell. 5th edn. Abingdon: Garlan Science. pg 1071, 1072, 1073.</ref>. Spindle fibres are signalled by the cell to lengthen causing the identical sister chromatids of each [[Chromosome|chromosome]] to be pulled toward opposite poles of the spindle. This occurs by the centromeres splitting and getting pulled to the opposite poles of the cell towards the centrioles. These processes contribute to chromosome segregation. The two groups that now lie in each end of the spindle contain the same number of [[Chromosome|chromosomes]] that were present in the original [[Interphase|interphase]] nucleus<ref>Johnson, A. et al. (2008) The Cell. 5th edn. Abingdon: Garlan Science. pg 1071, 1072, 1073.</ref>.  
+
[[Proteins|Proteins]] holding the [[Chromatids|chromatids]] together dissolve and [[Centromeres|centromeres]] separate (This is also known as [[Disjunction|disjunction]]). The [[Kinetochore]] microtubules begin to get shorter and shorter, at the same time the [[Spindle_fibres|spindle fibres]] also get shorter and therefore move apart<ref>Johnson, A. et al. (2008) The Cell. 5th edn. Abingdon: Garlan Science. pg 1071, 1072, 1073.</ref>. Spindle fibres are signalled by the cell to lengthen causing the identical sister chromatids of each [[Chromosome|chromosome]] to be pulled toward opposite poles of the spindle. This occurs by the centromeres splitting and getting pulled to the opposite poles of the cell towards the centrioles. These processes contribute to chromosome segregation. The two groups that now lie in each end of the spindle contain the same number of [[Chromosome|chromosomes]] that were present in the original [[Interphase|interphase]] nucleus<ref>Johnson, A. et al. (2008) The Cell. 5th edn. Abingdon: Garlan Science. pg 1071, 1072, 1073.</ref>.  
  
 
Above shows the four stages of mitosis<ref>http://www.accessexcellence.org/RC/VL/GG/mitosis.php</ref>.  
 
Above shows the four stages of mitosis<ref>http://www.accessexcellence.org/RC/VL/GG/mitosis.php</ref>.  
  
=== [[Telophase|Telophase]] ===
+
=== [[Telophase|Telophase]] ===
  
 
In this final stage of mitosis, a [[Nuclear envelope|nuclear envelope]] forms around each group of [[Chromosome|chromosomes]] and [[Cytokinesis|cytokinesis]] occurs, where the [[Cytoplasm|cytoplasm]] divides into two. The [[Spindle|spindle]] completely disappears and [[Chromosome|chromosomes]] undergo the reversal of condensation, deeming them no longer visible under the light microscope. At the end of telophase, the two separate daughter cells assume interphase appearance with fully developed [[Nucleoli|nucleoli]].  
 
In this final stage of mitosis, a [[Nuclear envelope|nuclear envelope]] forms around each group of [[Chromosome|chromosomes]] and [[Cytokinesis|cytokinesis]] occurs, where the [[Cytoplasm|cytoplasm]] divides into two. The [[Spindle|spindle]] completely disappears and [[Chromosome|chromosomes]] undergo the reversal of condensation, deeming them no longer visible under the light microscope. At the end of telophase, the two separate daughter cells assume interphase appearance with fully developed [[Nucleoli|nucleoli]].  
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=== [[Cytokinesis|Cytokinesis ]]  ===
 
=== [[Cytokinesis|Cytokinesis ]]  ===
  
The two individual nuclear envelopes are now formed again with the same amount of chromosomes in each. The cytoplasm now splits to form the two cells by a contractile ring of actin and myosin filaments, this 'pinches' the cell in two forming the two identical daughter cells<ref>Johnson, A. et al. (2008) The Cell. 5th edn. Abingdon: Garlan Science. pg 1071, 1072, 1073.</ref>.
+
The two individual nuclear envelopes are now formed again with the same amount of chromosomes in each. The cytoplasm now splits to form the two cells by a contractile ring of [[Actin|actin]] and [[Myosin|myosin]] filaments, this 'pinches' the cell in two forming the two identical daughter cells<ref>Johnson, A. et al. (2008) The Cell. 5th edn. Abingdon: Garlan Science. pg 1071, 1072, 1073.</ref>.  
  
=== References ===
+
=== References ===
  
 
<references />
 
<references />

Revision as of 08:54, 6 December 2017

Mitosis is the process of nuclear division that produces two identical daughter cells with a diploid complement of chromosomes from the parent cell. Cytokinesis usually occurs with mitosis, this is the process where the cell itself divides in order to yield two daughter cells. Mitosis only occurs in somatic tissues which are ordinary body cells, such as, liver cells, skin cells, etc[1]. In multicellular eukaryotic cells mitosis is a way for cells to repairing tissues, to accommodate for growing organisms, embryonic development, production of reticulocytes and to form identical cells to replace dying cells. In unicellular eukaryotic organisms, for example, yeast, mitosis is a way to reproduce asexually[2]. Check it out on The Mitosis Cycle on YouTube. It can be broken down into four main stages seen in animal cells:

Contents

Interphase

If a cell is not undergoing mitotic cell division, the cell is in interphase. In this phase, the chromosomes are invisible through a light microscope[3].

Interphase constitutes for most of the cell cycle;

It is the preparation period preceding mitosis, in which the cell grows and it's DNA is replicated. Interphase can be divided into 3 main phases;

G1( gap phase 1 ), S ( synthesis phase ) and G2 ( gap phase 2).

During Gap phase 1 biosynthetic activity in the cell is increased as the cell grows and replicates it's organelles whilst producing spare proteins.

During S phase the cell must replicate its DNA, in order for the two daughter cells produced via the following division to have a complete set of genetic material. Chromosomes are duplicated during this same phase, this produces 2 sister chromatids, allowing each daughter cell which results from the mitotic division to have the diploid number of chromosomes.

During Gap phase 2 the cell continues to grow and it produces specific proteins necessary for cell division so that mitosis can follow interphase.

Another vital event which occurs during interphase is that the cell repairs any DNA damage, to ensure that no undesirable mutations are passed on to the progeny cells[4].

Prophase

During interphase, the chromosomes are already doubled, this has two closely associated subunits called chromatids. Each pair of chromatids is a product from duplication of one chromosome in the S phase from interphase. These chromatids are held together by the centromere[5]. Throughout the process of prophase the chromosomes condense meaning they get shorten and thicken to form visibly distinct threads within the nucleus. This is brought about by the action of large proteins called condensins. Each </span>chromosome at this point consists of two </span>chromatids held together at the </span>centromere (central point). Meanwhile, outside the nucleus, the mitotic spindles assemble this is between the two centrioles. The centrioles have replicated and moved apart in order to do this.

Prometaphase

The beginning of prometaphase includes the breakdown of the nuclear envelope, this, therefore, means the spindle microtubules from the centrioles can attach to the centromere of the chromosomes. This is by kinetochores which then undergo active movement. The centrioles are at opposite poles when this stage begins. During this phase chromosomes are recognisable as double structures[6].

The four phases of mitosis.

Metaphase

The mitotic spindle consisting of microtubules formed by the polymerization of tubulin begins to form. There are three types of microtubule in the spindle:

  1. Anchor (centrosome to cell membrane)
  2. Arch (between centrosomes)
  3. Attachment ( to chromosomes)

NB. Centrosomes are located at the ends/poles of the spindle and are microtubule organising centres where tubulin polymerisation is initiated. These Centrosomes are formed by duplication of one centrosome during interphase.

The microtubules form when new tubulin subunits are added to the growing end. However, this can become unstable and the process of depolymerization can be initiated causing the polymer to shrink. This process is regulated by a number of proteins that maintain a balance between polymerization and depolymerization[7].

The next step in metaphase is the formation of the kinetochore, a site of attachment between the chromosome and the spindle microtubules[8]. Only chromosomal microtubules that make contact with the kinetochore however, will become stabilised and others will depolymerise.

The final part involves a position near to the centre of the cell, known as the metaphase plate. The kinetochore signals for each chromosome to move to the plate via dephosphorylation of certain proteins. The cell can then only move on to anaphase when all kinetochores are under tension and are aligned on the metaphase plate.

Anaphase

Proteins holding the chromatids together dissolve and centromeres separate (This is also known as disjunction). The Kinetochore microtubules begin to get shorter and shorter, at the same time the spindle fibres also get shorter and therefore move apart[9]. Spindle fibres are signalled by the cell to lengthen causing the identical sister chromatids of each chromosome to be pulled toward opposite poles of the spindle. This occurs by the centromeres splitting and getting pulled to the opposite poles of the cell towards the centrioles. These processes contribute to chromosome segregation. The two groups that now lie in each end of the spindle contain the same number of chromosomes that were present in the original interphase nucleus[10].

Above shows the four stages of mitosis[11].

Telophase

In this final stage of mitosis, a nuclear envelope forms around each group of chromosomes and cytokinesis occurs, where the cytoplasm divides into two. The spindle completely disappears and chromosomes undergo the reversal of condensation, deeming them no longer visible under the light microscope. At the end of telophase, the two separate daughter cells assume interphase appearance with fully developed nucleoli.

Cytokinesis

The two individual nuclear envelopes are now formed again with the same amount of chromosomes in each. The cytoplasm now splits to form the two cells by a contractile ring of actin and myosin filaments, this 'pinches' the cell in two forming the two identical daughter cells[12].

References

  1. Hartl, D. Ruvolo, M. (2012) Genetics. Burlington: Jones and; Bartlett learning. pg 119, 120
  2. Hartl, D. Ruvolo, M. (2012) Genetics. Burlington: Jones and; Bartlett learning. ph 119, 120
  3. Hartl, D. Ruvolo, M. (2012) Genetics. Burlington: Jones and Bartlett learning. pg 119, 120
  4. AS-Level Biology-The revision guide.Cumbria: Coordination group publications Ltd. 2. Hartl, D.L. and Ruvolo, M,2011.Genetics-analysis of genes and genomes.8th ed.Burlington MA: Jones and Bartlett Learning.
  5. Johnson, A. et al. (2008) The Cell. 5th edn. Abingdon: Garlan Science. pg 1071, 1072, 1073.
  6. Johnson, A. et al. (2008) The Cell. 5th edn. Abingdon: Garlan Science. pg 1071, 1072, 1073.
  7. Hartl, D. Ruvolo, M. (2012)Genetic: analysis of Genes and Genomes 8th edition jones and bartlett learning USA
  8. http://www.ncbi.nlm.nih.gov/pubmed/16214339
  9. Johnson, A. et al. (2008) The Cell. 5th edn. Abingdon: Garlan Science. pg 1071, 1072, 1073.
  10. Johnson, A. et al. (2008) The Cell. 5th edn. Abingdon: Garlan Science. pg 1071, 1072, 1073.
  11. http://www.accessexcellence.org/RC/VL/GG/mitosis.php
  12. Johnson, A. et al. (2008) The Cell. 5th edn. Abingdon: Garlan Science. pg 1071, 1072, 1073.
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