Lecture Notes: Cell Walls - Gram-Positive and Gram-Negative

Introduction

• Speaker: Dr. O
• Focus: Cell walls of bacteria, specifically gram-positive and gram-negative.
• Function of Cell Wall:
  • Bacteria cell membranes lack cholesterol; hence without cell walls, cells would lyse easily.
  • Antibiotics often target cell walls to cause bacterial cells to rupture.

Peptidoglycan (Murine) Structure

• Components:
  • Peptide: Protein component
  • Glycan: Carbohydrate component
  • Analogy: Carbohydrate backbone (logs) tied by protein components (rope).
• Importance:
  • Common in both gram-positive and gram-negative bacteria, but structures differ.

Gram-Positive Bacteria

• Characteristics:
  • Thick peptidoglycan cell wall.
  • Provides better mechanical protection.
• Defense Mechanism:
  • Mainly mechanical due to thick cell wall.
• Concerns:
  • Some gram-positive bacteria are dangerous, but less research focused compared to gram-negative.

Gram-Negative Bacteria

• Characteristics:
  • Thin peptidoglycan cell wall.
  • Presence of periplasmic space between plasma membrane and cell wall.
  • Outer lipid membrane (LPS membrane):
    • Strong negative charge.
• Periplasmic Space:
  • Contains degradative enzymes and transport proteins.
  • Can break down and pump out harmful substances including antibiotics.
• Outer Membrane (LPS):
  • Evades phagocytosis and complement system.
  • Acts as a barrier to detergents, heavy metals, bile salts, certain antibiotics, and lysozyme.
• Lipid A Toxin:
  • Endotoxin released upon cell death.
  • Can cause fever, blood clotting, dilation of blood vessels, and shock.
  • Care is needed when treating infections to prevent rapid toxin release.

Summary

• Gram-Positive:
  • Thick cell walls offer physical protection.
• Gram-Negative:
  • More susceptible to mechanical stress but protected by outer membrane and endotoxins.
  • More resistant to immune responses and treatments.
• Current Focus:
  • Majority of research on combating gram-negative bacteria due to their resistance and danger.

Conclusion

• Separate video will cover atypical cell walls.
• Takeaway: Understanding the structural differences helps in targeting bacterial infections effectively.