Lecture Notes: Bacterial Cell Structures

Glycocalyx

• Definition: A sugar coat outside the cell wall, viscous and sticky, comes in two forms:
  • Capsule: Rigid, well-defined structure.
  • Slime Layer: Looser and less ordered.
• Functions:
  • Contributes to virulence by helping bacteria evade phagocytosis.
  • Assists with cell attachment.
  • Prevents cells from drying out.
• Biofilms:
  • Associated with both slime layers and virulence.
  • Reduce sensitivity to antibiotics and detergents.
  • Formation involves many bacteria joining together with their slime layers.

Flagella

• Definition: Filamentous protein structures that allow bacterial movement.
• Types:
  • Monotrichous: Single flagellum, polar.
  • Amphitrichous: Flagella on either end.
  • Lophotrichous: Multiple flagella at one end.
  • Peritrichous: Flagella spread over the surface.
• Movement Mechanism:
  • Chemotaxis: Movement towards/away from chemicals.
  • Phototaxis: Movement towards/away from light.
  • Flagellar rotation leads to 'runs' and 'tumbles' to navigate.
• Swarming Characteristics:
  • Seen in highly motile bacteria like Proteus mirabilis.
  • In lab, it displays wave-like movements across petri plates.

Axial Filaments

• Found in some bacteria, inside the cell.
• Examples include:
  • Lyme Disease: Borrelia burgdorferi.
  • Syphilis: Treponema pallidum.

Other External Structures

Fimbriae

• Role: Helps in bacterial adhesion to surfaces.
• Significance in Virulence:
  • Example: Neisseria gonorrhoeae adheres to the urogenital tract using fimbriae.

Pili

• Function: Involved in lateral gene transfer.
• Mechanism:
  • Facilitate the transfer of plasmid DNA between bacteria.
  • Important for spreading traits like antibiotic resistance.
• Example: Antibiotic resistance gene sharing.

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• Focus on eukaryotic cells and their primary substructures.