Structure:
* Filament: A long, helical structure composed of the protein flagellin. This is the visible part of the flagellum.
* Hook: A curved structure connecting the filament to the basal body. It acts as a flexible joint allowing the flagellum to rotate.
* Basal Body: A complex structure embedded in the cell membrane and cell wall. It consists of a rod and a series of rings (two in Gram-negative bacteria and one in Gram-positive bacteria). The basal body serves as the motor for flagellar rotation.
Mechanism of Rotation:
* Proton motive force: Prokaryotic flagella are powered by a proton gradient across the cell membrane. This gradient is established by processes like respiration and photosynthesis.
* Rotary motor: The basal body functions as a rotary motor, using the proton gradient to generate torque and rotate the flagellum.
Movement:
* Rotation: Flagella can rotate either clockwise or counterclockwise.
* Swimming: Counterclockwise rotation causes the flagella to bundle together and propel the cell forward in a smooth, straight line.
* Tumbling: Clockwise rotation causes the flagella to become unbundled and the cell to tumble randomly.
* Run-and-tumble: The alternating phases of running and tumbling allow bacteria to move in a biased random walk, allowing them to explore their environment.
Other features:
* Number and arrangement: Bacteria can have different numbers and arrangements of flagella, such as peritrichous (multiple flagella all over the cell), polar (a single flagellum at one end), or lophotrichous (a cluster of flagella at one end).
* Structure variation: Some bacteria have flagella with specialized structures like sheaths or hooks, which influence their motility.
It's important to note that the detailed structure and function of flagella can vary slightly between bacterial species.
