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.
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
Three 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.
Flagellum Media
Prokaryotic (bacterial and archaeal) flagella run in a rotary movement, while eukaryotic flagella run in a bending movement. The prokaryotic flagellum uses a rotary motor, and the eukaryotic flagellum uses a complex sliding filament system.
Eukaryotic flagella. 1–axoneme, 2–cell membrane, 3–IFT (IntraFlagellar Transport), 4–Basal body, 5–Cross section of flagella, 6–Triplets of microtubules of basal body
Cross section of an axoneme
Longitudinal section through the flagella area in Chlamydomonas reinhardtii. In the cell apex is the basal body that is the anchoring site for a flagellum. Basal bodies originate from and have a substructure similar to that of centrioles, with nine peripheral microtubule triplets (see structure at bottom center of image).
The "9+2" structure is visible in this cross-section micrograph of an axoneme.
Beating pattern of eukaryotic "flagellum" and "cillum", a traditional distinction before the structures of the two are known.
Physical model of a bacterial flagellum
References
- ↑ 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.
{{cite journal}}: 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
- 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