Question

A bacterial flagellum is composed of

• A. Filament, hook and basal body
• B. Vesicles, tubules and lamellae
• C. Pili, Fimbriae and filament
• D. Hook, tubules and Fimbriae

Answer 1

The Correct Option is A

A bacterial flagellum is a complex motility appendage responsible for propelling the bacterium through a liquid medium. It consists of three main structural parts: 

1. Filament: This is the long, helical, whip-like structure that extends outwards from the cell surface. It is composed primarily of repeating subunits of the protein flagellin. The rotation of the filament generates the thrust for movement.
2. Hook: This is a curved, flexible structure that acts as a universal joint, connecting the filament to the basal body. It transmits the torque generated by the motor to the filament, allowing it to rotate.
3. Basal Body: This is the motor complex embedded within the cell envelope (cell wall and plasma membrane). It anchors the flagellum to the cell and contains the protein rings and motor proteins (like Mot proteins) that utilize proton motive force (or sometimes sodium motive force) to generate the rotation of the hook and filament.

Now let's examine the options provided:

• Filament, hook and basal body: This option correctly lists the three main components of the bacterial flagellum.
• Vesicles, tubules and lamellae: These are general cellular structures not specific to the bacterial flagellum composition.
• Pili, Fimbriae and filament: Pili and fimbriae are other types of bacterial surface appendages, distinct from flagella.
• Hook, tubules and Fimbriae: Tubules (like microtubules) are characteristic of eukaryotic flagella/cilia, not bacterial flagella. Fimbriae are different appendages.

Therefore, a bacterial flagellum is composed of Filament, hook and basal body.

Answer 2

A bacterial flagellum is primarily composed of three main parts:

• Filament: The long, whip-like structure that extends from the bacterial surface and is responsible for the movement of the bacterium.
• Hook: A curved structure that connects the filament to the basal body, allowing the flagellum to rotate.
• Basal body: The motor complex that anchors the flagellum to the bacterial cell membrane and is responsible for the rotation of the flagellum.

Thus, the correct answer is (A) : Filament, hook and basal body.