flagellum

/fleuh jel"euhm/, n., pl. flagella /-jel"euh/, flagellums.

1. Biol. a long, lashlike appendage serving as an organ of locomotion in protozoa, sperm cells, etc.

2. Bot. a runner.

3. Also called clavola. Entomol. (in an antenna) the whiplike portion above the basal joints.

4. a whip or lash.

[1800-10; < L: whip, lash, dim. of flagrum a whip, scourge]

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Hairlike structure that acts mainly as an organelle of movement in the cells of many living organisms.

Characteristic of the protozoan group Mastigophora, flagella also occur on the sex cells of algae, fungi (see fungus), mosses, and slime molds. Flagellar motion causes water currents necessary for respiration and circulation in sponges and cnidarians. Most motile bacteria move by means of flagella. The structures and patterns of movement of flagella in prokaryotes differ from those in eukaryotes. See also cilium.

The bacterium Proteus vulgaris (greatly magnified) showing flagella

© Lee D. Simon

Photo Researchers

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▪ cell

plural  flagella 

  hairlike structure that acts primarily as an organelle of locomotion in the cells of many living organisms. Flagella, characteristic of the protozoan group Mastigophora, also occur on the gametes of algae, fungi, mosses, slime molds, and animals. Flagellar motion causes water currents necessary for respiration and circulation in sponges and coelenterates. Most motile bacteria move by means of flagella.

      The structures and pattern of movement of prokaryotic (prokaryote) and eukaryotic flagella are different. Eukaryotes (eukaryote) have one to many flagella, which move in a characteristic whiplike manner. The flagella closely resemble the cilium (q.v.) in structure. The core is a bundle of nine pairs of microtubules surrounding two central pairs of microtubules (the so-called nine-plus-two arrangement); each microtubule is composed of the protein tubulin. The coordinated sliding of these microtubules confers movement. The base of the flagellum is anchored to the cell by a basal body.

      Bacterial flagella are helically shaped structures containing the protein flagellin. The base of the flagellum (the hook) near the cell surface is attached to the basal body enclosed in the cell envelope. The flagellum rotates in a clockwise or counterclockwise direction, in a motion similar to that of a propeller.

      The movement of eukaryotic flagella depends on adenosine triphosphate (ATP) for energy, while that of the prokaryotes derives its energy from the proton-motive force, or ion gradient, across the cell membrane.

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