Overview
This lecture introduces the basics of bacterial flagella structure, their function in motility, and how bacteria move using run and tumble behavior.
Structure of Bacterial Flagella
- All bacterial flagella have three main parts: filament, hook, and basal body.
- The filament is the long, whip-like structure visible outside the cell.
- The hook connects the filament to the basal body and acts as a flexible joint.
- The basal body anchors the flagellum to the cell and enables rotation.
- Rotation is powered by the flow of hydrogen ions (protons) through the basal body, similar to ATP synthase.
- Gram-positive bacteria have a simpler flagellar structure due to a thick cell wall.
- Gram-negative bacteria have a more complex flagellar structure to span the outer membrane and periplasmic space.
Function and Purpose of Flagella
- Flagella provide motility (ability to move) for bacteria.
- Bacteria move to seek attractants (e.g., nutrients, oxygen) or avoid repellents (e.g., waste products).
- Movement towards chemicals is called chemotaxis; movement towards or away from light is phototaxis.
Mechanism of Bacterial Movement
- Bacteria move using a pattern called "run and tumble."
- A "run" occurs when flagella rotate counterclockwise, moving the cell in one direction.
- A "tumble" happens when flagella rotate clockwise, causing the cell to stop and change direction.
- Run allows long movement towards or away from stimuli; tumble enables quick changes in direction.
Key Terms & Definitions
- Flagella — whip-like appendages that enable bacterial movement.
- Filament — long, external part of the flagellum.
- Hook — flexible connector between filament and basal body.
- Basal Body — motor structure embedded in the cell wall/membrane for flagellar rotation.
- Motility — ability of an organism to move independently.
- Chemotaxis — movement toward or away from chemicals.
- Phototaxis — movement toward or away from light.
- Run — straight, sustained movement; flagella rotate counterclockwise.
- Tumble — random change in direction; flagella rotate clockwise.
Action Items / Next Steps
- Review diagrams of flagellar structure in both gram-positive and gram-negative bacteria.
- Study examples of chemotaxis and run/tumble movement patterns.