Transmission electron microscope studies have shown that
the bacterial flagellum is composed of three parts (figure 3.42).
The longest and most obvious portion is the filament, which
extends from the cell surface to the tip. The basal body is embedded
in the cell; and a short, curved segment, the hook,
links the filament to its basal body and acts as a flexible coupling.
The filament is a hollow, rigid cylinder constructed of subunits of
the protein fl agellin, which ranges in molecular weight from
30,000 to 60,000 daltons, depending on the bacterial species. The
filament ends with a capping protein. Some bacteria have sheaths
surrounding their flagella. For example, Vibrio cholerae has a
lipopolysaccharide sheath.