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Bacterial Flagellum

More than actomyosin or tubulokinesin, the bacterial flagellum of Salmonella typhimurium is the analogue of a man-made mechanical system. Its heart is a 15,000 revolutions per minute, reversible rotary motor powered by the proton-motive gradient across the cell's inner membrane. Each revolution consumes about 1000 protons. A drive shaft, held by a bushing in the outer membrane, transmits torque across the cell's envelope. Attached to the drive shaft, a universal joint enables the motor to drive the propeller, even when the drive shaft and propeller are not co-linear. A short junction joins the propeller to the drive shaft. The propeller, a long left-handed corkscrew, converts torque to thrust. A cap sits at the cell distal end of the filament. By electron microscopy, the motor associated parts and the bushing are seen to be rings of subunits, whereas the drive shaft appears to be a helical assembly of subunits. About four dozen genes are needed to build the flagellum. Some are required for regulation of synthesis; some for export and assembly; some for the structure itself, and a few are of unknown function. Nineteen different proteins are known to be part of the flagellar structure; it is thought that there may be additional components*.

*Quoted From: DeRosier D. Spinning Tails. Curr Opin Struct Biol. 1995 Apr;5(2):187-93

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