Structure and Function of Flagella in Bacteria

Structure of Flagella in Bacteria:

May forms of bacteria bear thin, elongated thread-like flagella which help in their locomotion. Almost all the spirilla, most of the bacilli, and some of the cocci are flagellate. The flagella are fixed on to be protoplast and arise from small basal granules, the blepharoplasty situated on the outside of the cytoplasm.

The flagella may consist of either a simple filament or 2-3 fibrils coiled helically. In some forms, they twist to form a thick bundle. Bacteria having no flagella are termed atrichous, those with only one polar flagellum are monotrichous, such a group of flagella at one end lophotrichous, with a group of flagella at both ends, amphitrichos and with flagella uniformly distributed all over the body are termed peritrichous.

Function of Flagella in Bacteria:

Many bacteria are actively motile, moving at speed of up to 50mμ/second. Such bacteria are normally found to possess flagella. Bacteria flagella are much smaller than eukaryotic flagella, being about 120-180 A° in diameter, they don’t show the 9 plus 2 patterns of fibrils are not enclosed in a membrane, and show no ATPase activity.

Bacterial flagella consist essentially of a pure protein called “flagellin”. The flagella of motile bacteria are distributed over the surface of the cell in a characteristic fashion. The flagellum pierces the cell wall and arises from a specialized area of the cytoplasm, sometimes called a blepharoplasty by analogy with higher organisms flagella. Depending upon the arrangement of flagella, they may be atrichous, monotrichous, lophotrichous, amphitrichous at both poles and finally peritrichous.