Microtubule

2018-12-05T14:34:41Z

180155648: Changes to punctuation

[[Image:Screen Shot 2017-12-04 at 11.40.37.png|thumb|right]] The figure to the right shows 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>

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 ===

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 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 ===

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 the [[Trachea|trachea]] and [[Fallopian tube|fallopian tube]]. The cilia are attached 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>.

=== References ===

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Microtubule