Microtubule

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Microtubules are a co<span style="font-size: 13.28px;">mponent of the cells </span>[[Cytoskeleton|cytoskeleton]]<span style="font-size: 13.28px;">, which is responsible for vital </span>[[Cell|cell]]<span style="font-size: 13.28px;"> functions, such as cell structure, shape, and transport.</span>
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Microtubules are a component of the cells [[Cytoskeleton|cytoskeleton]] , which is responsible for vital [[Cell|cell]] functions, such as cell structure, shape, and transport.  
  
=== Structure of Microtubules ===
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=== Structure of Microtubules ===
  
 
Microtubules are hollow cylinder-shaped polymers that are made up of [[Globular protein|globular protein]] subunits called [[Tubulin|tubulin]]. Each tubulin subunit, which are also known as [[Heterodimer|heterodimers]], consist of one alpha-tubulin and one beta tubulin<ref>Cooper GM. The Cell: A Molecular Approach. 2nd Ed. London: ASM Press. 2000.</ref>. Alpha-tubulin always attaches to beta-tubulin, with beta-tubulin always attaching to alpha-tubulin. Microtubules have both a positive end, where beta-tubulin is exposed and a negative end, where alpha tubulin is exposed<ref>http://study.com/academy/lesson/microtubules-definition-functions-structure.html</ref>. This means that microtubules are polar structures because of the positive and negative ends.  
 
Microtubules are hollow cylinder-shaped polymers that are made up of [[Globular protein|globular protein]] subunits called [[Tubulin|tubulin]]. Each tubulin subunit, which are also known as [[Heterodimer|heterodimers]], consist of one alpha-tubulin and one beta tubulin<ref>Cooper GM. The Cell: A Molecular Approach. 2nd Ed. London: ASM Press. 2000.</ref>. Alpha-tubulin always attaches to beta-tubulin, with beta-tubulin always attaching to alpha-tubulin. Microtubules have both a positive end, where beta-tubulin is exposed and a negative end, where alpha tubulin is exposed<ref>http://study.com/academy/lesson/microtubules-definition-functions-structure.html</ref>. This means that microtubules are polar structures because of the positive and negative ends.  
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Microtubules are 25 nm in length and 14 nm in width, making them the largest cytoskeletal filaments found in [[Eukaryotic cells|eukaryotic cells]]<ref>Cooper GM. The Cell: A Molecular Approach. 2nd Ed. London: ASM Press. 2000.</ref>.  
 
Microtubules are 25 nm in length and 14 nm in width, making them the largest cytoskeletal filaments found in [[Eukaryotic cells|eukaryotic cells]]<ref>Cooper GM. The Cell: A Molecular Approach. 2nd Ed. London: ASM Press. 2000.</ref>.  
  
=== Function of Microtubules ===
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=== Function of Microtubules ===
  
Microtubules have different functions. They are most commonly found as [[Cilia|cilia]] and [[Flagella|flagella ]]. Cilia, which are short, hair<span style="font-size: 13.28px;">-like structures,</span><span style="font-size: 13.28px;">are found in place</span><span style="font-size: 13.28px;">s such as t</span><span style="font-size: 13.28px;">he </span>[[Trachea|trachea]]<span style="font-size: 13.28px;"> and </span>[[Fallopian tube|fallopian tube]]<span style="font-size: 13.28px;">. T</span><span style="font-size: 13.28px;">he cilia are attach</span>[[Image:Screen Shot 2017-12-04 at 11.40.37.png|thumb|left]]<span style="font-size: 13.28px;">ed to the </span>[[Basal body|basal body]]<span style="font-size: 13.28px;"> and stick outwards of the cell surface, where they beat back and forth. This assists the removal of </span>[[Mucus|mucus]]<span style="font-size: 13.28px;"> in the </span>[[Trachea|trachea]]<span style="font-size: 13.28px;">, and allows for an </span>[[Egg cell|egg cell]]<span style="font-size: 13.28px;"> to move through the </span>[[Fallopian tube|fallopian tube]]<ref>Nigg EA. Centrioles, Centrosomes, and Cilia in Health and Disease. 2009. [cited 20 November 2016]; Available from: http://www.sciencedirect.com/science/article/pii/S0092867409013622</ref><span style="font-size: 13.28px;">. In flagella, microtubules form the long tail, which is necessary for </span>[[Sperm cell|sperm cells to]]<span style="font-size: 13.28px;"> propel themselves towards egg cells for </span>[[Fertilisation|fertilisation]]<span style="font-size: 13.28px;">.</span>
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Microtubules have different functions. They are most commonly found as [[Cilia|cilia]] and [[Flagella|flagella ]]. Cilia, which are short, hair -like structures, are found in place s such as t he [[Trachea|trachea]] and [[Fallopian tube|fallopian tube]] . T he cilia are attach [[Image:Screen Shot 2017-12-04 at 11.40.37.png|thumb|left|Screen Shot 2017-12-04 at 11.40.37.png]] ed to the [[Basal body|basal body]] and stick outwards of the cell surface, where they beat back and forth. This assists the removal of [[Mucus|mucus]] in the [[Trachea|trachea]] , and allows for an [[Egg cell|egg cell]] to move through the [[Fallopian tube|fallopian tube]]<ref>Nigg EA. Centrioles, Centrosomes, and Cilia in Health and Disease. 2009. [cited 20 November 2016]; Available from: http://www.sciencedirect.com/science/article/pii/S0092867409013622</ref> . In flagella, microtubules form the long tail, which is necessary for [[Sperm cell|sperm cells to]] propel themselves towards egg cells for [[Fertilisation|fertilisation]] .  
  
 
Both cilia and flagella have the [[9+2 arrangement|9+2 arrangement ]], which is observed in cross sections when the [[Axoneme|axoneme]] is cut. As shown in Figure 1, the 9+2 arrangement consists of a central singlet microtubule inside the cilia/flagella, and 9 surrounding doublet microtubules<ref>Lodish H, Berk A, Zipursky SL, Matsudaira P, Baltimore D, Darnell J. Molecular Cell Biology. 4th Ed. New York: W H Freeman and Company. 2000.</ref>. [[Dynein|Dyneins]] attached to the inside and outside of the 9 doublet microtubules enable microtubules of the 9+2 arrangement to bend, which is why cilia can beat back and forth and why flagella, accompanied with [[ATP|ATP]], can propel the sperm cell. Without the 9+2 arrangement, microtubules can only slide vertically on each other and cannot bend like cilia and flagella<ref>Lodish H, Berk A, Zipursky SL, Matsudaira P, Baltimore D, Darnell J. Molecular Cell Biology. 4th Ed. New York: W H Freeman and Company. 2000.</ref>.  
 
Both cilia and flagella have the [[9+2 arrangement|9+2 arrangement ]], which is observed in cross sections when the [[Axoneme|axoneme]] is cut. As shown in Figure 1, the 9+2 arrangement consists of a central singlet microtubule inside the cilia/flagella, and 9 surrounding doublet microtubules<ref>Lodish H, Berk A, Zipursky SL, Matsudaira P, Baltimore D, Darnell J. Molecular Cell Biology. 4th Ed. New York: W H Freeman and Company. 2000.</ref>. [[Dynein|Dyneins]] attached to the inside and outside of the 9 doublet microtubules enable microtubules of the 9+2 arrangement to bend, which is why cilia can beat back and forth and why flagella, accompanied with [[ATP|ATP]], can propel the sperm cell. Without the 9+2 arrangement, microtubules can only slide vertically on each other and cannot bend like cilia and flagella<ref>Lodish H, Berk A, Zipursky SL, Matsudaira P, Baltimore D, Darnell J. Molecular Cell Biology. 4th Ed. New York: W H Freeman and Company. 2000.</ref>.  
  
===  ===
 
  
Figure 1 - The 9+2 arrangement of microtubules  
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Figure 1 - The 9+2 arrangement of microtubules in cilia and flagella<ref>Lodish H, Berk A, Zipursky SL, Matsudaira P, Baltimore D, Darnell J. Molecular Cell Biology. 4th Ed. New York: W H Freeman and Company. 2000.</ref>
  
in cilia and flagella&nbsp;<ref>Lodish H, Berk A, Zipursky SL, Matsudaira P, Baltimore D, Darnell J. Molecular Cell Biology. 4th Ed. New York: W H Freeman and Company. 2000.</ref>
 
  
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=== References ===
  
=== References  ===
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Revision as of 08:31, 5 December 2017

Microtubules are a component of the cells cytoskeleton , which is responsible for vital cell functions, such as cell structure, shape, and transport.

Structure of Microtubules

Microtubules are hollow cylinder-shaped polymers that are made up of globular protein subunits called tubulin. Each tubulin subunit, which are also known as heterodimers, consist of one alpha-tubulin and one beta tubulin[1]. Alpha-tubulin always attaches to beta-tubulin, with beta-tubulin always attaching to alpha-tubulin. Microtubules have both a positive end, where beta-tubulin is exposed and a negative end, where alpha tubulin is exposed[2]. This means that microtubules are polar structures because of the positive and negative ends.

Microtubules are 25 nm in length and 14 nm in width, making them the largest cytoskeletal filaments found in eukaryotic cells[3].

Function of Microtubules

Microtubules have different functions. They are most commonly found as cilia and flagella . Cilia, which are short, hair -like structures, are found in place s such as t he trachea and fallopian tube . T he cilia are attach
Screen Shot 2017-12-04 at 11.40.37.png
ed to the basal body and stick outwards of the cell surface, where they beat back and forth. This assists the removal of mucus in the trachea , and allows for an egg cell to move through the fallopian tube[4] . In flagella, microtubules form the long tail, which is necessary for sperm cells to propel themselves towards egg cells for fertilisation .

Both cilia and flagella have the 9+2 arrangement , which is observed in cross sections when the axoneme is cut. As shown in Figure 1, the 9+2 arrangement consists of a central singlet microtubule inside the cilia/flagella, and 9 surrounding doublet microtubules[5]. Dyneins attached to the inside and outside of the 9 doublet microtubules enable microtubules of the 9+2 arrangement to bend, which is why cilia can beat back and forth and why flagella, accompanied with ATP, can propel the sperm cell. Without the 9+2 arrangement, microtubules can only slide vertically on each other and cannot bend like cilia and flagella[6].


Figure 1 - The 9+2 arrangement of microtubules in cilia and flagella[7]


References

  1. Cooper GM. The Cell: A Molecular Approach. 2nd Ed. London: ASM Press. 2000.
  2. http://study.com/academy/lesson/microtubules-definition-functions-structure.html
  3. Cooper GM. The Cell: A Molecular Approach. 2nd Ed. London: ASM Press. 2000.
  4. Nigg EA. Centrioles, Centrosomes, and Cilia in Health and Disease. 2009. [cited 20 November 2016]; Available from: http://www.sciencedirect.com/science/article/pii/S0092867409013622
  5. Lodish H, Berk A, Zipursky SL, Matsudaira P, Baltimore D, Darnell J. Molecular Cell Biology. 4th Ed. New York: W H Freeman and Company. 2000.
  6. Lodish H, Berk A, Zipursky SL, Matsudaira P, Baltimore D, Darnell J. Molecular Cell Biology. 4th Ed. New York: W H Freeman and Company. 2000.
  7. Lodish H, Berk A, Zipursky SL, Matsudaira P, Baltimore D, Darnell J. Molecular Cell Biology. 4th Ed. New York: W H Freeman and Company. 2000.
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