2.5 Flagella

🎯 What Are Flagella?

• Flagella (singular: flagellum) are tail-like structures used by many bacteria to move.
• They work like little motors that spin and push the bacteria forward.
• Besides movement, they also help bacteria sense and respond to chemical signals (chemotaxis).

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🔍 Types of Bacteria Based on Flagella

1. Atrichous – No flagella at all.
2. Monotrichous – One flagellum at one end.
3. Lophotrichous – A bunch of flagella at one end.
4. Amphitrichous – One flagellum on each end.
5. Peritrichous – Flagella all around the cell.

(Think of them like different hairstyles: ponytail, pigtails, full curls!)

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🛠️ Structure of Bacterial Flagellum

The flagellum of bacteria is very different from the flagellum in human cells.

• It is made of a protein called flagellin.
• It does not have the 9+2 microtubule arrangement found in eukaryotic cells.

Let’s look at the three main parts:

1. Basal Body
   • The part anchored inside the cell membrane.
   • Acts like a motor that rotates the flagellum.
   • Has rotating rings:
     • 1 pair in Gram-positive bacteria.
     • 2 pairs in Gram-negative bacteria.
2. Hook
   • A curved part that connects the basal body to the filament.
   • Works like a universal joint, allowing flexible movement.
3. Filament
   • The long tail-like structure.
   • Whips around to push the cell forward.