Gram-Positive vs. Gram-Negative Cell Walls

What are the characteristics of Gram-positive bacteria in Gram staining?

They stain purple and have a thick peptidoglycan layer in their cell wall.

What are the characteristics of Gram-negative bacteria in Gram staining?

They stain pink and have a thin peptidoglycan layer and an outer membrane in their cell wall.

How does the cell wall structure of Gram-positive bacteria affect their sensitivity to penicillin and lysozyme?

Gram-positive bacteria are more sensitive to both penicillin and lysozyme because their thick, exposed peptidoglycan layer is a direct target.

How does the cell wall structure of Gram-negative bacteria affect their resistance to antibiotics and enzymes?

Gram-negative bacteria are more resistant due to their outer membrane barrier, which protects their thin peptidoglycan layer from direct access.

What key feature of peptidoglycan makes it an excellent antibiotic target?

Peptidoglycan is unique to bacteria, meaning antibiotics can target it specifically without harming host cells.

What is the primary function of the peptidoglycan cell wall in bacteria?

It provides rigidity, which helps bacteria resist osmotic lysis (bursting) by maintaining cell shape and integrity against internal pressure.

What are the basic sugar building blocks of peptidoglycan's backbone?

They are NAG (N-acetylglucosamine) and NAM (N-acetylmuramic acid), linked in long alternating chains.

How is the peptidoglycan structure strengthened by cross-linking?

It's strengthened by short peptide chains (tetrapeptide side chains) that cross-link the NAM units, forming a robust "chain-link fence" structure.

What is the specific action of lysozyme on the peptidoglycan cell wall?

Lysozyme cuts the glycosidic bonds between NAG and NAM units, thereby weakening the peptidoglycan backbone.

How do penicillin and
β-lactam antibiotics impair the bacterial cell wall?

Penicillin and
β-lactam antibiotics prevent the formation of peptide cross-links between the NAM units, which compromises the integrity and rigidity of the peptidoglycan wall.

What is the consequence for a bacterium if its peptidoglycan cell wall is weakened or improperly formed?

A weakened or improperly formed wall causes the bacterium to lose its rigidity and become susceptible to osmotic lysis (bursting), especially in hypotonic environments.