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Wednesday, 10 July 2019

Bacterial Flagella: structure, types and function

Bacterial Flagella: structure, types and function

Rabotanyteach.blogspot.com

  • Flagellum (singular) is hair like helical structure emerges from cell wall and cell membrane
  • It is responsible for motility of the bacteria
  • Size: thin 15-20nm in diameter.
  • Single flagella can be seen with light microscope only after staining with special stain which increase the diameter of flagella.

Structure of flagella:


  • Flagella is not straight but is helical.
  • It is composed of flagellin protein (globular protein) and known as H antigen.
  • Flagella has three parts. Basal body, Hook and filament

Basal body:

  • it is composed of central rod inserted into series of rings which is attached to cytoplasmic memvbrane and cell wall.
  • L-ring: it is the outer ring present only in Gram -ve bacteria, it anchored in lipopolysaccharide layer
  • P-ring: it is second ring anchored in peptidoglycan layer of cell wall.
  • M-S ring: anchored in cytoplasmic membrane
  • C ring: anchored in cytoplasm
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Hook:

  • it is the wider region at the base of filament
  • it connects filament to the motor protein in the base
  • length of hook is longer in gram +ve bacteria than gram –ve bacteria

Filament:

  • it is thin hair like structure arises from hook.

Types of flagella

On the basis of arrangement

1. Monotrichous:

  • presence of single flagella in one end of cell.
  • examples; Vibrio cholera, Pseudomonas aerogenosa

2. Lophotrichous:

  • presence of bundle of flagella in one end of cell.
  • example: Pseudomanas fluroscence

3. Amphitrichous:

  • presence of single or cluster of flagella at both end of cell.
  • example; Aquaspirillium

4. Peritrichous:

  • presence of flagella all over the cell surface.
  •   example; E.coli, Salmonella, Klebsiella

5. Atrichous:

  • absent of flagella.
  • example; Shigella

Function:

Flagellar motility:

  • At the base surrounding the inner ring (M-S and C ring) there is a series of protein called Mot protein.
  • A final set of protein called Fli protein function as motor switch. The flagella motor rotates the filament as a turbine causing movement of the cell in the medium.
  • The movement of flagella results from rotation of basal body which is similar to the movement of the shaft of an electric motor.
  • A turning motion is generated between S-ring and M ring. S-ring acts as starter while M ring acts as roter.
  • The basal body as a whole give a universal joint to the cell and allows complete rotation of hook and filament.
  • Flagella moves the cell by rotating the flagella about the basal body. Rotation of flagella is either clockwise or anticlockwise

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