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Encyclopedia > Flagellum

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A flagellum (plural: flagella) is a long, slender projection from the cell body, which can be directly seen (or rendered visible after appropriate treatment) with the light or electron microscope. Its function is usually to propel a unicellular or small multicellular organism by beating with a whip-like motion. In larger animals, the flagella are often arranged en masse at the surface of a stationary cell anchored within an organ and serve to move fluids along mucous membranes, such as the lining of the trachea. Insects display a wide variety of antennal shapes. ... The cell body or soma is a structure in a neuron consisting of the main part of the cell and containing the nucleus. ... For other uses, see Whip (disambiguation). ... A fluid is defined as a substance that continually deforms (flows) under an applied shear stress regardless of the magnitude of the applied stress. ... The mucous membranes (or mucosa) are linings of ectodermic origin, covered in epithelium, that line various body cavities and internal organs. ... Windpipe redirects here. ...


Three quite distinct 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.
  • Archaeal flagella are superficially similar to bacterial flagella, but are different in many details and considered non-homologous.
  • Eukaryotic flagella - those of animal, plant, and protist cells - are complex cellular projections that lash back and forth.

Sometimes eukaryotic flagella are called cilia or undulipodia to emphasize their distinctiveness. Phyla/Divisions Actinobacteria Aquificae Bacteroidetes/Chlorobi Chlamydiae/Verrucomicrobia Chloroflexi Chrysiogenetes Cyanobacteria Deferribacteres Deinococcus-Thermus Dictyoglomi Fibrobacteres/Acidobacteria Firmicutes Fusobacteria Gemmatimonadetes Nitrospirae Omnibacteria Planctomycetes Proteobacteria Spirochaetes Thermodesulfobacteria Thermomicrobia Thermotogae Bacteria (singular, bacterium) are a major group of living organisms. ... Phyla Crenarchaeota Euryarchaeota Korarchaeota Nanoarchaeota ARMAN The Archaea (), or archaebacteria, are a major group of microorganisms. ... In biology, homology is any similarity between structures that is due to their shared ancestry. ... Kingdoms Animalia - Animals Fungi Plantae - Plants Chromalveolata Protista Alternative phylogeny Unikonta Opisthokonta Metazoa Choanozoa Eumycota Amoebozoa Bikonta Apusozoa Cabozoa Rhizaria Excavata Corticata Archaeplastida Chromalveolata Animals, plants, fungi, and protists are eukaryotes (IPA: ), organisms whose cells are organized into complex structures by internal membranes and a cytoskeleton. ... Not to be confused with Psyllium. ...


Bacterial flagellum

Examples of bacterial flagella arrangement schemes. A-Monotrichous; B-Lophotrichous; C-Amphitrichous; D-Peritrichous;
Examples of bacterial flagella arrangement schemes. A-Monotrichous; B-Lophotrichous; C-Amphitrichous; D-Peritrichous;

The bacterial flagellum is made up of the protein flagellin. Its shape is a 20 nanometer-thick hollow tube. It is helical and has a sharp bend just outside the outer membrane; this "hook" allows the helix to point directly away from the cell. A shaft runs between the hook and the basal body, passing through protein rings in the cell's membrane that act as bearings. Gram-positive organisms have 2 of these basal body rings, one in the peptidoglycan layer and one in the plasma membrane. Gram-negative organisms have 4 such rings: the L ring associates with the lipopolysaccharides, the P ring associates with peptidoglycan layer, the M ring is imbedded in the plasma membrane, and the S ring is directly attached to the plasma membrane. The filament ends with a capping protein. Image File history File links Flagella. ... Image File history File links Flagella. ... A representation of the 3D structure of myoglobin, showing coloured alpha helices. ... Helicobacter pylori electron micrograph, showing multiple flagella on the cell surface Flagellin is a protein that arranges itself in a hollow cylinder to form the filament in bacterial flagellum. ... (Redirected from 1 E -8 m) To help compare different orders of magnitude this page lists lengths between 10 nm and 100 nm (10-8 and 10-7 m). ... A nanometre (American spelling: nanometer) is 1. ... A helix (pl: helices), from the Greek word έλικας/έλιξ, is a twisted shape like a spring, screw or a spiral (correctly termed helical) staircase. ... A basal body is a short cylindrical array of microtubules plus their associated proteins found at the base of a eukaryotic cell cilium or flagellum. ... Gram-positive bacteria are those that are stained dark blue or violet by gram staining, in contrast to gram-negative bacteria, which are not affected by the stain. ... Peptidoglycan, also known as murein, is a polymer consisting of sugars and amino acids that forms a mesh-like layer outside the plasma membrane of eubacteria. ... Drawing of a cell membrane A component of every biological cell, the cell membrane (or plasma membrane) is a thin and structured bilayer of phospholipid and protein molecules that envelopes the cell. ... Bacteria that are Gram-negative are not stained dark blue or violet by Gram staining, in contrast to Gram-positive bacteria. ... The L-ring of the bacterial flagellum is the ring in the lipid outer cell membrane through which the axial filament (rod, hook, and flagellum) passes. ... A lipopolysaccharide (LPS) is a large molecule that contains both lipid and a carbohydrate. ... Peptidoglycan, also known as murein, is a polymer consisting of sugars and amino acids that forms a mesh-like layer outside the plasma membrane of eubacteria. ... Drawing of a cell membrane A component of every biological cell, the cell membrane (or plasma membrane) is a thin and structured bilayer of phospholipid and protein molecules that envelopes the cell. ...


The bacterial flagellum is driven by a rotary engine is made up of protein (Mot complex), located at the flagellum's anchor point on the inner cell membrane. The engine is powered by proton motive force, i.e., by the flow of protons (e.g., hydrogen ions) across the bacterial cell membrane due to a concentration gradient set up by the cell's metabolism (in Vibrio species the motor is a sodium ion pump rather than a proton pump). The rotor transports protons across the membrane, and is turned in the process. The rotor alone can operate at 6,000 to 17,000 rpm, but with the flagellar filament attached usually only reaches 200 to 1000 rpm. Flagella do not rotate at a constant speed but instead can increase or decrease their rotational speed in relation to the strength of the proton motive force. Flagella rotation can move bacteria through liquid media at speed of up to 60 cell lengths/second (sec). Although this is only about 0.00017 km/h, when comparing this speed with that of higher organisms in terms of number of lengths moved per second, it is extremly fast. The fastest animal, the cheetah, moves at a maximum rate of about 110 km/h, but this represents only about 25 body lengths/sec. Thus, when size is accounted for, prokaryotic cells swimming at 50-60 lengths/sec are actually much faster than larger organisms. A representation of the 3D structure of myoglobin, showing coloured alpha helices. ... Look up cell membrane in Wiktionary, the free dictionary. ... Electrochemical gradients in cellular biology refers to the electrical and chemical properties across a membrane. ... For other uses, see Proton (disambiguation). ... This article is about the chemistry of hydrogen. ... This article is about the electrically charged particle. ... A concentration gradient is the difference in density of a substance over a distance. ... Vibrio is a genus of bacteria, included in the gamma subgroup of the Proteobacteria. ... For sodium in the diet, see Edible salt. ... Sputter ion pumps are a class of vacuum pump designed to operate in very low pressure (i. ... proton gradient: Pink represents the matrix while the red dots represent protons. ... For other uses, see Revolutions per minute (disambiguation). ...


The components of the bacterial flagellum are capable of self-assembly without the aid of enzymes or other factors. Both the basal body and the filament have a hollow core, through which the component proteins of the flagellum are able to move into their respective positions. During assembly, protein components are added at the flagellar tip rather than at the base. Neuraminidase ribbon diagram An enzyme (in Greek en = in and zyme = blend) is a protein, or protein complex, that catalyzes a chemical reaction and also controls the 3D orientation of the catalyzed substrates. ...


The basal body has several traits in common with some types of secretory pores, such as the hollow rod-like "plug" in their centers extending out through the plasma membrane. Given the structural similarities, it was thought that bacterial flagella may have evolved from such pores; however, it is now known that these pores are derived from flagella. Secretion is the process of segregating, elaborating, and releasing chemicals from a cell, or a secreted chemical substance or amount of substance. ...


Different species of bacteria have different numbers and arrangements of flagella. Monotrichous bacteria have a single flagellum (e.g., Vibrio cholerae). Lophotrichous bacteria have multiple flagella located at the same spot on the bacteria's surfaces which act in concert to drive the bacteria in a single direction. Amphitrichous bacteria have a single flagellum on each of two opposite ends (only one flagellum operates at a time, allowing the bacteria to reverse course rapidly by switching which flagellum is active). Peritrichous bacteria have flagella projecting in all directions (e.g., Escherichia coli). Binomial name Vibrio cholerae Pacini 1854 Vibrio cholerae is a gram negative bacterium with a curved-rod shape that causes cholera in humans. ... E. coli redirects here. ...


In some bacteria, such as Selenomonas, the flagella are organized outside the cell body, twining about each other into a structure called a "fascicle." Other bacteria, such as Spirochetes, have a specialized type of flagellum called an "axial filament" that is located in the periplasmic space, the rotation of which causes the entire bacterium to move forward in a corkscrew-like motion. Species[1] Selenomonas acidaminovorans Selenomonas artemidis Selenomonas dianae Selenomonas flueggei Selenomonas infelix Selenomonas lacticifex Selenomonas lipolytica Selenomonas noxia Selenomonas ruminantium Selenomonas sputigena The genus Selenomonas constitutes a group of motile crescent-shaped bacteria within the Acidaminococcaceae family and include species living in the gastrointestinal tracts of animals. ... The word fascicle derives from the Latin fascis (bundle). Fascicles are the sections of a book, usually a reference work, that because of its length, is issued in parts so that the information may be made available to the public as soon as possible rather than waiting years or decades... Families Brachyspiraceae Leptospiraceae Spirochaetaceae The spirochaetes are a phylum of distinctive bacteria, which have long, helically coiled cells. ... The periplasmic space is the space seen between the plasma membrane and the outer membrane in the gram-negative bacteria. ...


Counterclockwise rotation of monotrichous polar flagella thrust the cell forward with the flagella trailing behind. Periodically, the direction of rotation is briefly reversed, causing what is known as a "tumble" in which the cell seems to thrash about in place. This results in the reorientation of the cell. When moving in a favorable direction, "tumbles" are unlikely; however, when the cell's direction of motion is unfavorable (e.g., away from a chemical attractant), a tumble may occur, with the chance that the cell will be thus reoriented in the correct direction.


Archaeal flagellum

The archaeal flagellum is superficially similar to the bacterial (or eubacterial) flagellum; in the 1980s they were thought to be homologous on the basis of gross morphology and behavior (Cavalier-Smith, 1987). Both flagella consist of filaments extending outside of the cell, and rotate to propel the cell. Phyla Crenarchaeota Euryarchaeota Korarchaeota Nanoarchaeota ARMAN The Archaea (pronounced ) are a major group of microorganisms. ...


However, discoveries in the 1990s have revealed numerous detailed differences between the archaeal and bacterial flagella; these include:

  • Bacterial flagella are powered by a flow of H+ ions (or occasionally Na+ ions); archaeal flagella are almost certainly powered by ATP. The torque-generating motor that powers rotation of the archaeal flagellum has not been identified.
  • While bacterial cells often have many flagellar filaments, each of which rotates independently, the archaeal flagellum is composed of a bundle of many filaments that rotate as a single assembly.
  • Bacterial flagella grow by the addition of flagellin subunits at the tip; archaeal flagella grow by the addition of subunits to the base.
  • Bacterial flagella are thicker than archaeal flagella, and the bacterial filament has a large enough hollow "tube" inside that the flagellin subunits can flow up the inside of the filament and get added at the tip; the archaeal flagellum is too thin to allow this.
  • Many components of bacterial flagella share sequence similarity to components of the type III secretion systems, but the components of bacterial and archaeal flagella share no sequence similarity. Instead, some components of archaeal flagella share sequence and morphological similarity with components of type IV pili, which are assembled through the action of type II secretion systems (the nomenclature of pili and protein secretion systems is not consistent).

These differences mean that the bacterial and archaeal flagella are a classic case of biological analogy, or convergent evolution, rather than homology. However, in comparison to the decades of well-publicized study of bacterial flagella (e.g. by Berg), archaeal flagella have only recently begun to get serious scientific attention. Therefore, many assume erroneously that there is only one basic kind of prokaryotic flagellum, and that archaeal flagella are homologous to it. For example, Cavalier-Smith (2002) is aware of the differences between archaeal and bacterial flagellins, but retains the misconception that the basal bodies are homologous.[citation needed] This article is about the chemistry of hydrogen. ... This article is about the electrically charged particle. ... For sodium in the diet, see Edible salt. ... Adenosine 5-triphosphate (ATP) is a multifunctional nucleotide that is most important as a molecular currency of intracellular energy transfer. ... For other senses of this word, see torque (disambiguation). ... Analogy is both the cognitive process of transferring information from a particular subject (the analogue or source) to another particular subject (the target), and a linguistic expression corresponding to such a process. ... In evolutionary biology, convergent evolution is the process whereby organisms not closely related, independently evolve similar traits as a result of having to adapt to similar environments or ecological niches. ... In biology, homology is any similarity between structures that is due to their shared ancestry. ...


Eukaryotic flagellum

The eukaryotic flagellum is completely different from the prokaryote flagellum in both structure and evolutionary origin. The only shared characteristics among bacterial, archaeal, and eukaryotic flagella are their superficial appearance; they are intracellular extensions used in creating movement. Along with cilia, they make up a group of organelles known as undulipodia. Image File history File links Flagellum_base_diagram. ... Image File history File links Flagellum_base_diagram. ... cross-section of two cilia, showing 9+2 structure A cilium (plural cilia) is a fine projection from a eukaryotic cell that constantly beats in one direction. ... Diagram of a cross-section of the axoneme microtubule array present in all undulipodia An undulipodium is an intracellular projection of a eukaryotic cell containing a microtubule array. ...


A eukaryotic flagellum is a bundle of nine fused pairs of microtubule doublets surrounding two central single microtubules. The so-called "9+2" structure is characteristic of the core of the eukaryotic flagellum called an axoneme. At the base of a eukaryotic flagellum is a basal body, "blepharoplast" or kinetosome, which is the microtubule organizing center (MTOC) for flagellar microtubules and is about 500 nanometers long. Basal bodies are structurally identical to centrioles. The flagellum is encased within the cell's plasma membrane, so that the interior of the flagellum is accessible to the cell's cytoplasm. Each of the outer 9 doublet microtubules extends a pair of dynein arms (an "inner" and an "outer" arm) to the adjacent microtubule; these dynein arms are responsible for flagellar beating, as the force produced by the arms causes the microtubule doublets to slide against each other and the flagellum as a whole to bend. These dynein arms produce force through ATP hydrolysis. The flagellar axoneme also contains radial spokes, polypeptide complexes extending from each of the outer 9 mictrotubule doublets towards the central pair, with the "head" of the spoke facing inwards. The radial spoke is thought to be involved in the regulation of flagellar motion, although its exact function and method of action are not yet understood. Microtubules are one of the components of the cytoskeleton. ... An axoneme is the core scaffold of the eukaryotic cilia and flagella, which are projections from the cell made up of microtubules. ... A basal body is a short cylindrical array of microtubules plus their associated proteins found at the base of a eukaryotic cell cilium or flagellum. ... MTOC or microtubule-organizing center is a structure found in all plant and animal cells from which microtubules radiate. ... A centriole showing the nine triplets of microtubules. ... Drawing of a cell membrane A component of every biological cell, the cell membrane (or plasma membrane) is a thin and structured bilayer of phospholipid and protein molecules that envelopes the cell. ... Cross section of cell with cytoplasm labeled at center right. ... Dynein is a motor protein (also called molecular motor or motor molecule) in cells which converts the chemical energy contained in ATP into the mechanical energy of movement. ... Hydrolysis is a chemical reaction or process in which a chemical compound is broken down by reaction with water. ... The radial spoke is a multi-unit protein structure found in the axonemes of eukaryotic cilia and flagella. ...


Motile flagella serve for the propulsion of single cells (e.g. swimming of protozoa and spermatozoa) and the transport of fluids (e.g. transport of mucus by stationary flagellated cells in the trachea).


Additionally, immotile flagella are vital organelles in sensation and signal transduction across a wide variety of cell types (e.g. eye: rod photoreceptor cells, nose: olfactory receptor neurons, ear: kinocilium in cochlea). In biophysics, transduction is the conveyance of energy from one electron (a donor) to another (a receptor), at the same time that the class of energy changes. ...


Intraflagellar transport (IFT), the process by which axonemal subunits, transmembrane receptors, and other proteins are moved up and down the length of the flagellum, is essential for proper functioning of the flagellum, in both motility and signal transduction. Intraflagellar Transport or IFT refers to the cellular process essential for the formation and maintenance of eukaryotic cilia and flagella. ... Transmembrane receptors are integral membrane proteins, which reside and operate typically within a cells plasma membrane, but also in the membranes of some subcellular compartments and organelles. ...


For information on biologists' ideas about how the various flagella may have evolved, see evolution of flagella. The evolution of flagella is of great interest to biologists because the three known varieties of flagella (eukaryotic, bacterial, and archaebacterial) each represent an extremely sophisticated cellular structure that requires the interaction of many different and finely-tuned systems to function correctly. ...


See also

The evolution of flagella is of great interest to biologists because the three known varieties of flagella (eukaryotic, bacterial, and archaebacterial) each represent an extremely sophisticated cellular structure that requires the interaction of many different and finely-tuned systems to function correctly. ...

References

^ This article incorporates content from the 1728 Cyclopaedia, a publication in the public domain.


External links


  Results from FactBites:
 
flagellum (1213 words)
The components of the flagellum are capable of self-assembly in which the component proteins associate spontaneously without the aid of enzymes or other factors.
The archaeal flagellum is superficially similar to the bacterial flagellum; in the 1980s they were thought to be homologous on the basis of gross morphology and behavior.
A eukaryotic flagellum is a bundle of nine fused pairs of microtubules doublets surrounding two central single microtubules.
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