Flagellum
A flagellum (plural: flagella) is a long, whip-like structure that helps some single celled organisms move. It is composed of microtubules. They help propel cells and organisms in a whip-like motion. The flagellum of eukaryotes usually moves with an “S” motion, and is surrounded by cell membrane.
![](http://upload.wikimedia.org/wikipedia/commons/thumb/9/93/Flagellum-beating.png/240px-Flagellum-beating.png)
Flagella are structurally almost identical with the much smaller Cilia. So much so that it has been proposed protists bearing either should be unified in the Phylum Undulipodia.[1] Previously, Margulis had proposed that the Ciliates alone should be placed in a Phylum Ciliophora.[2] Admittedly, the Protista is a collection of disparate single-celled forms, but while a more sophisticated taxonomy is in flux (changing), Protista is still a useful term.
Cilia and flagella are cell organelles, specialised units which carry out well-defined functions, like mitochondria and plastids. It is fairly clear now that all or most of these organelles have their origin in once-independent prokaryotes (bacteria or archaea), and that the eukaryote cell is a 'community of micro-organisms' working together in 'a marriage of convenience'.[3]
Types
changeThree types of flagella have so far been distinguished; bacterial, archaeal and eukaryotic. The main differences among these three types are summarized below:
- Bacterial flagella are helical filaments that rotate like screws.[4][5][6] They provide two of several kinds of bacterial motility.[7][8]
- Archaeal flagella are superficially similar to bacterial flagella, but are different in many details and considered non-homologous.[9][10][11]
- Eukaryotic flagella – those of animal, plant, and protist cells – are complex cellular projections that lash back and forth. Eukaryotic flagella are classed along with eukaryotic motile cilia as undulipodia[12] to emphasize their distinctive wavy appendage role in cellular function or motility. Primary cilia are immotile, and are not undulipodia; they have a structurally different 9+0 axoneme rather than the 9+2 axoneme found in both flagella and motile cilia undulopodia.
References
change- ↑ Margulis L & Dolan M.F. 2002. Early life: evolution on the Precambrian Earth. 2nd ed, Jones & Bartlett, Boston. p89
- ↑ Margulis L. Schwartz K.V. & Dolan M. 1999. Diversity of life: the illustrated guide to the five kingdoms. Jones & Bartlett, Boston, p94. In this work the authors propose 19 phyla for the Protista, and call this 'Kingdom' the 'Protoctista', a term which is unfortunately almost unpronounceable.
- ↑ Margulis L. and McMenamin 1990. Marriage of convenience. The Sciences 30, 31-36.
- ↑ Silverman M. & Simon M (1974). "Flagellar rotation and the mechanism of bacterial motility". Nature. 249 (452): 73–74. Bibcode:1974Natur.249...73S. doi:10.1038/249073a0. PMID 4598030. S2CID 10370084.
- ↑ Meister GLM, Berg HC (1987). "Rapid rotation of flagellar bundles in swimming bacteria". Nature. 325 (6105): 637–640. Bibcode:1987Natur.325..637L. doi:10.1038/325637a0. S2CID 4242129.
- ↑ Berg HC, Anderson RA (1973). "Bacteria swim by rotating their flagellar filaments". Nature. 245 (5425): 380–382. Bibcode:1973Natur.245..380B. doi:10.1038/245380a0. PMID 4593496. S2CID 4173914.
- ↑ Jahn TL, Bovee EC (1965). "Movement and locomotion of microorganisms". Annual Review of Microbiology. 19: 21–58. doi:10.1146/annurev.mi.19.100165.000321. PMID 5318439.
- ↑ Harshey RM (2003). "Bacterial motility on a surface: many ways to a common goal". Annual Review of Microbiology. 57: 249–273. doi:10.1146/annurev.micro.57.030502.091014. PMID 14527279.
- ↑ Ng SY, Chaban B, Jarrell KF (2006). "Archaeal flagella, bacterial flagella and type IV pili: a comparison of genes and posttranslational modifications". J. Mol. Microbiol. Biotechnol. 11 (3–5): 167–91. doi:10.1159/000094053. PMID 16983194. S2CID 30386932.
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: CS1 maint: multiple names: authors list (link) - ↑ Metlina AL (2004). "Bacterial and archaeal flagella as prokaryotic motility organelles". Biochemistry Mosc. 69 (11): 1203–12. doi:10.1007/s10541-005-0065-8. PMID 15627373. S2CID 632440.
- ↑ Jarrell; et al. (2009). "Archaeal flagella and pili". Pili and flagella: current research and future trends. Caister Academic Press. ISBN 978-1-904455-48-6.
- ↑ A Dictionary of Biology, 2004, accessed 2011-01-01.
Other websites
change- Molecular Machines Index of Illustrations, Graphics, and Animations
- Physics Today introduction to the bacterial flagellum by Howard Berg Archived 2004-06-18 at the Wayback Machine