The motility of bacteria is provided by the flagella, a rigid helical structure that extends up to 10 microns out from the cell. Flagella allow cells to move towards nutrients or away from harmful substances such as acids in a process known as chemotaxis. Flagella are less than .2 microns thick and therefore are below the resolution of the light microscope. In order for the flagella to be viewed they must be stained using a special procedure. A single flagellum is composed of a rigid filament that occurs in the form a single helix. This makes up the main body of the flagellum structure. The filament is connected to a hook that is attached to a shaft that is inserted into a series of rings. The shaft is inserted into a series of rings. The number of rings differs depending on whether the cell is gram-positive or gram-negative. The shaft rings along with other accessory proteins make up the basal body of the flagellum. Proteins associated with the basal body transport protons across the cell membrane which creates a charge differential. This charge differential forces the rings to rotate which results in the rotation of the shaft, hook, and filament.
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