Axoneme
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224945268
2008-07-11T03:20:53Z
Sentausa
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add micrograph picture
[[Image:Chlamydomonas TEM 17.jpg|thumb|Micrograph of thin x-section cut through ''Chlamydomonas'' axoneme]]
[[Image:Axoneme.JPG|thumb|Schematic figure of axoneme cross section]]
Numerous [[eukaryotic]] [[Cell (biology)|cells]] carry whip-like appendages ([[cilia]] or [[eukaryotic]] [[flagella]]) whose inner core consists of a [[cytoskeleton|cytoskeletal]] structure called the '''axoneme'''.
The axoneme serves as the "skeleton" of these [[organelles]], both giving support to the structure and, in some cases, causing it to bend. Though distinctions of function and/or length may be made between cilia and flagella, the internal structure of the axoneme is common to both.
The building block of the axonmene is the [[microtubule]]; each axoneme is composed of several microtubules aligned in [[parallel]]. More specifically, the microtubules are arranged in a characteristic pattern known as the “9x2 + 2," as shown in the image at right. Nine sets of "doublet" microtubules (a specialized structure consisting of two linked microtubules) form a ring around a "central pair" of single microtubules.
Besides the microtubules, the axoneme contains many [[protein]]s and protein complexes necessary for its function. The [[dynein]] arms, for example, are motor complexes which produce the force needed for bending. Each dynein arm is anchored to a doublet microtubule; by "walking" along an adjacent microtubule, the dynein motors can cause the microtubules to slide against each other. When this is carried out in a synchronized fashion, with the microtubules on one side of the axonmene being pulled 'down' and those on the other side pulled 'up,' the axoneme as a whole can bend back and forth. This process is responsible for ciliary/flagellar beating, as in the well-known example of the [[human sperm]].
The [[radial spoke]] is another protein complex of the axoneme. Thought to be important in regulating the motion of the axoneme, this "T"-shaped complex projects from each set of outer doublets toward the central microtubules.
The axoneme structure in non-motile [[primary cilium]] shows some variation from the canonical “9x2 + 2” anatomy. No dynein arms are found on the outer doublet microtubules, and there is no pair of central microtubule singlets. This organization of axoneme is referred as “9x2 + 0”. In addition, “9x2 + 1” axonemes, with only a single central microtubule, have been found to exist.
==Further reading==
{{cite journal|title=Betting on cilia|author=Vogel, G.|volume=310|year=2005|journal=Science}}
{{cite journal|title=The 9 + 2 Axoneme Anchors Multiple Inner Arm Dyneins and a Network of Kinases and Phosphatases that Control Motility|author=Porter, M.E. and Sale, W.S.|volume=151|pages=F37–42|year=2000|journal=The Journal of Cell Biology|pmid = 11086017|doi=10.1083/jcb.151.5.F37}}
{{cite journal|title=An Integrative Model of Internal Axoneme Mechanics and External Fluid Dynamics in Ciliary Beating|author=Dillon, R.H. and Fauci, L.J.|year=2000|journal=Journal Theoretical Biology|volume=207|pages=415–30|pmid=11082310|doi=10.1006/jtbi.2000.2182}}
{{cite journal|title=Rotation of the Central Pair Microtubules in Eukaryotic Flagella|author=Omoto, C.K., Gibbons, I.R., Kamiya, R., Shingyoji, C., Takahashi, K., and Witman, G.B.|year=1999|journal=Molecular Biology Cell|volume=10|pages=1–4|pmid=9880321}}
{{cite journal|title=Intraflagellar transport: the eyes have it|author=Rosenbaum, J.L., Cole, D.G., and Diener D.R.|year=1999|journal=Journal of Cell Biology|volume=1999|pages=385–8|pmid=9971734|doi=10.1083/jcb.144.3.385}}
[[Category:Organelles]]
[[es:Axonema]]
[[eu:Axonema]]
[[fr:Axonème]]
[[lt:Aksonema]]
[[pl:Aksonema]]
[[pt:Axonema]]
[[ru:Аксонема]]