Vlagella

Vlagella, commonly known as flagella, are slender, whip-like organelles that enable cells to move. The term vlagella is sometimes used as an alternate spelling or in non-English contexts, but flagella is the standard term in English.

Bacterial flagella consist of a basal body anchored in the cell envelope, a hook, and a long filament made of flagellin. The motor at the base rotates the flagellum, powered by a proton motive force or, in some species, a sodium gradient, producing propulsion. Bacterial motility includes runs and tumbles, regulated by chemotaxis and environmental cues.

Archaea have flagella, sometimes called archaella, that function similarly to bacterial flagella but are structurally distinct. They are typically thinner and composed of archaellins, and they are powered by ATP hydrolysis rather than the proton motive force used by many bacteria. Archaella generally produce rotation to move the cell, though detailed mechanisms can vary among species.

Eukaryotic flagella are structurally different: they contain an axoneme with nine outer microtubule doublets arranged around a central pair (9+2). Dynein motor proteins drive microtubule sliding, producing bending waves that propel the cell. Eukaryotic flagella beat in an undulating pattern and are typically longer and fewer in number than many bacterial flagella. They do not rotate like bacterial motors.

Flagella support diverse biological roles, including locomotion for single-celled organisms, fertilization in many animals, and sensory functions that guide movement in response to chemical, light, or temperature cues. They are important in ecology, pathogenesis, and biotechnology, and remain a major focus of cell biology and evolutionary studies.