Motility refers to the ability of organisms to move actively, consuming energy in the process. There are structural and functional differences between prokaryotic and eukaryotic motilities.
Prokaryotic motility. Many prokaryotes are motile due to the presence of a special structure, the flagellum; certain prokaryotic cells can move along solid substances by gliding, and planktonic microorganisms can also regulate their position in a water column using gas vesicles. Prokaryotic flagella are long, thin helical appendages attached to the cell at one end. Flagella can have a polar (attached to one or both cellular ends) or a peritrichous (inserted around the cell) position. The filaments of prokaryotic flagella are composed of subunits of a protein called flagellin. In Bacteria, flagellin is highly conserved, suggesting that motility has deep evolutionary roots. However, in Archaea, several different flagellins have been described, and the...