flagellar

Flagellar refers to flagellum, a long, whip-like organelle used for locomotion by a wide range of organisms. In bacteria and archaea, flagella are proteinaceous structures that enable self-propulsion; in many protists and some algae, flagella are also used for movement or feeding.

Prokaryotic flagella are helical filaments assembled outside the cell envelope. They rotate like a propeller and are driven by a motor in the cell membrane that uses the proton motive force (or sodium motive force in some species). The basal body anchors the motor, the hook transmits torque to the filament, and the filament is mainly composed of flagellin subunits. The motor involves stator proteins such as MotA/MotB and rotor components; rotation results in propulsion, with changes in direction controlled by switching the rotation from counterclockwise to clockwise in many species.

Eukaryotic flagella (and cilia) are built from a cytoskeletal axoneme with a 9+2 arrangement of microtubules, powered by dynein motors. They are longer and more complex than bacterial flagella and rely on intraflagellar transport for assembly and maintenance. They generate bending waves that propel the cell through fluid.

Archaea possess flagella, or archaella, that resemble bacterial motility structures in function but are structurally distinct and typically powered by ATP hydrolysis rather than a proton motive force.

Flagellar motility influences ecological interactions, pathogenesis, and development, and flagellin, the primary filament protein in some bacteria, is a known immune stimulant in hosts.