Bacterial Flagella

A lot of bacterial  cells have one or more tail-like  appendages  known  as flagella.  bacteria  can move through  the extracellular  medium towards  attractants  and  away  from  repellents, By rotating  their flagella so called  chemotaxis. Bacterial flagella are different from flagella and eukaryotic cilia in two ways:

(1)  Each bacterial flagellum is composed of the protein flagellin (53 kDa subunit) as opposed to  tubule in  and 

(2)  it  rotates  rather  than  bends. 

An E. Coli bacterium on  the surface of the cell has  approximate  six  flagella  that  emerge  from  various  positions. Flagella are thin helical filaments which is 15 nm in diameter and 10 μm long. Electron microscopy has revealed that the flagellar  filament  have eleven subunits in 2 helical turns which, when viewed end-on, has the appearance with a hollow central core of an 11-bladed propeller. By the addition  of  new  flagellin  subunits  to  the  end  away  from  the  cell Flagella grow,  with  the  new subunits  diffusing  through  the central core. membrane  is the  flagellar  hook  composed  of subunits  of the  42 kDa hook  protein  that  forms  a  short,  curved  structure Between  the flagellar  filament  and the  cell which Situated   in the plasma membrane is the flagellar motor or basal body, an intricate assembly of proteins. The flexible hook is associated to a series of protein rings which are embedded in the outer and inner membranes.  By a flow of protons the rotation of the flagella is driven through an outer ring of proteins, known the stator. In the F₁F₀-ATPase a similar proton- driven motor is found that synthesizes ATP.

             Cell wall structure of (a) Gram-positive  and (b) Gram-negative  bacteria.