Flagellum
Say it: fluh-JEL-um
A flagellum is a long, whip-like projection that some cells, including many bacteria and sperm, use to swim through liquid.
Also: flagella
Definition
What is a flagellum?
A flagellum is a thin, tail-like structure that sticks out from a cell and drives it through fluid. Bacteria, archaea and many eukaryotic cells have flagella, but the three kinds are built differently and evolved separately. In bacteria the flagellum has three parts: a basal body anchored in the cell envelope, which works as a rotary motor; a short curved hook that acts as a joint; and a long, stiff, helical filament made of many thousands of copies of the protein flagellin. Ions, usually protons, flowing into the cell through the motor's stator units turn the rotor, and the filament spins like a propeller.
Bacteria are described by how their flagella are arranged: a single one at a pole (monotrichous, as in Vibrio cholerae), a tuft at one end (lophotrichous), flagella at both ends (amphitrichous) or all over the surface (peritrichous, as in E. coli). During chemotaxis, counterclockwise rotation bundles the filaments so the cell swims straight in a run, while clockwise rotation splays them so the cell tumbles and changes direction.
A eukaryotic flagellum, such as a sperm tail, is instead a whip that bends, powered by dynein motors acting on a 9 + 2 ring of microtubules inside the cell membrane.
Word parts
Where does the word “flagellum” come from?
- flagellum
- little whipLatin, diminutive of flagrum (whip)
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Terms that go with it
- BacteriumA bacterium is a single-celled prokaryote with no nucleus, found in almost every habitat on Earth, including in and on the human body.
- MicrotubuleA microtubule is a hollow tube built from the protein tubulin, one of the main cytoskeleton fibers, used for cell shape, transport and cell division.
- CytoskeletonThe cytoskeleton is a network of protein filaments inside a cell that gives it shape, holds organelles in place and powers movement and division.
- ProkaryoteA prokaryote is a usually single-celled organism, a bacterium or an archaeon, whose cell has no nucleus or other membrane-bound organelles.
- Gram-negative bacteriaGram-negative bacteria have a thin peptidoglycan wall wrapped in an outer membrane, so they lose the purple dye in a Gram stain and look pink.
- ProtozoaProtozoa are single-celled eukaryotes that do not photosynthesize, usually move on their own and feed on other organisms or organic matter.
Sources
Checked against
Written for biofideX in plain words, after checking these references:
- OpenStax Microbiology, 3.3 Unique Characteristics of Prokaryotic Cells
- Nakamura and Minamino, Flagella-Driven Motility of Bacteria (Biomolecules, 2019)
- OpenStax Biology 2e, 4.5 The Cytoskeleton
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