<Li> Eukaryotic flagella--those of animal, plant, and protist cells--are complex cellular projections that lash back and forth . Eukaryotic flagella are classed along with eukaryotic motile cilia as undulipodia to emphasize their distinctive wavy appendage role in cellular function or motility . Primary cilia are immotile, and are not undulipodia; they have a structurally different 9 + 0 axoneme rather than the 9 + 2 axoneme found in both flagella and motile cilia undulipodia . </Li> <P> The bacterial flagellum is made up of the protein flagellin . Its shape is a 20 - nanometer - thick hollow tube . It is helical and has a sharp bend just outside the outer membrane; this "hook" allows the axis of the helix to point directly away from the cell . A shaft runs between the hook and the basal body, passing through protein rings in the cell's membrane that act as bearings . Gram - positive organisms have two of these basal body rings, one in the peptidoglycan layer and one in the plasma membrane . Gram - negative organisms have four such rings: the L ring associates with the lipopolysaccharides, the P ring associates with peptidoglycan layer, the M ring is embedded in the plasma membrane, and the S ring is directly attached to the plasma membrane . The filament ends with a capping protein . </P> <P> The flagellar filament is the long, helical screw that propels the bacterium when rotated by the motor, through the hook . In most bacteria that have been studied, including the Gram - negative Escherichia coli, Salmonella typhimurium, Caulobacter crescentus, and Vibrio alginolyticus, the filament is made up of 11 protofilaments approximately parallel to the filament axis . Each protofilament is a series of tandem protein chains . However, Campylobacter jejuni has seven protofilaments . </P> <P> The basal body has several traits in common with some types of secretory pores, such as the hollow, rod - like "plug" in their centers extending out through the plasma membrane . Given the structural similarities between bacterial flagella and bacterial secretory systems, bacterial flagella may have evolved from the type - three secretion system; however, whether these pores are derived from the bacterial flagella or the bacterial secretory system is not known for certain . </P>

The filament of the bacterial flagellum are composed of
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