Flagella

Flagella are microscopic hair-like structures involved in the locomotion of a cell. The word “flagellum” means “whip”.

The flagella have a whip-like appearance that helps to propel a cell through the liquid. Some special flagella are used in few organisms as sensory organs that can sense changes in pH and temperature.

They are filamentous structures found in archaea, bacteria, and eukaryotes.

1. Archaeal flagella are nonhomologous.
2. Bacterial flagella are a coiled, thread-like structure, sharp bent, consisting of a rotary motor at its base and are composed of the protein flagellin.  A shaft exists between a hook and a basal body passing through the protein rings in the cell membrane.
3. Eukaryotic flagella are complicated cellular projections that pummel backwards and forward and are found in protist cells, gametes of plants, and animals. It is made up of a protein called tubulin.

The diagram of a sperm representing Flagella Structure at the posterior end

Bacterial Flagella Structure

The flagella is a helical structure composed of flagellin protein. The flagella structure is divided into three parts:

• Basal body
• Hook
• Filament

Basal Body

It is attached to the cell membrane and cytoplasmic membrane.

It consists of rings surrounded by a pair of proteins called MotB. The rings include:

L-ring: Outer ring anchored in the lipopolysaccharide layer and found in gram +ve bacteria.

P-ring: Anchored in the peptidoglycan layer.

C-ring: Anchored in the cytoplasm

M-S ring: Anchored in the cytoplasmic membrane

Hook

It is a broader area present at the base of the filament.

Connects filament to the motor protein in the base.

The hook length is greater in gram +ve bacteria.

Filament

Thin hair-like structure arising from the hook.

Also Read: Difference between cilia and flagella