Bacterial Structures

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.

Frederick Griffith's experiments were pivotal in understanding the phenomenon of bacterial transformation. He studied different strains of Streptococcus pneumoniae, specifically the virulent (pathogenic) strain and the non-virulent (avirulent) strain.

In his experiments, Griffith observed that when he injected mice with the heat-killed virulent strain of Streptococcus pneumoniae, the mice remained healthy and survived. Similarly, when he injected mice with the live avirulent strain, the mice also remained healthy.

However, Griffith discovered something intriguing when he injected mice with a mixture of the heat-killed virulent strain and the live avirulent strain. The mice became sick and died, and upon examination, he found live virulent bacteria in their bodies. This led Griffith to propose the concept of transformation, where the genetic material from the heat-killed virulent strain somehow transformed the avirulent strain into a virulent form.