The Science of Existence (93-2) Flagella


Other bacteria prosper with different propulsion: flagella with helical filaments, driven by a rotary engine anchored on the inner cell membrane.

Flagella and cilia both work in coordinated fashion, albeit differently. Cilia move with a complex 3-dimensional swim, propelling with a power and recovery stroke.

Flagella rotate like a propeller rather than beating back and forth. These flagella are helical, and revolve 200–1,000 times per minute, propelling bacteria as fast as 60 cell-lengths per second. A cheetah, the fastest land animal, has a top speed of 25 body lengths per second.

Though similar structurally, the proteins that make up cell tails differs between bacteria, archaea, and eukaryotes. This suggests that tails are an instance of convergent evolution: coming to the same solution independently.