10 Questions
What is the primary function of the periplasmic space in gram-negative bacteria?
To facilitate the breakdown of large macromolecules for metabolism
What is a characteristic of the outer membrane in gram-negative bacteria?
It is traversed by type I to V secretion devices
What is the primary function of lipoteichoic acids in gram-positive bacteria?
To initiate innate protective host responses
What is a characteristic of the gram-negative cell wall?
It is more complex than gram-positive cell walls
What is the primary function of type III secretion devices in gram-negative bacteria?
To transport molecules that facilitate bacterial adhesion or intracellular growth
What is the main function of the peptidoglycan in gram-positive bacteria?
To maintain the structure and shape of the cell
What is the effect of lysozyme on the peptidoglycan of gram-positive bacteria?
It cleaves the glycan backbone of the peptidoglycan
Which of the following molecules is NOT a component of the gram-positive bacterial cell wall?
Proteoglycans
What is the role of lipoteichoic acids in gram-positive bacteria?
They are anchored in the cytoplasmic membrane and promote attachment to mammalian cells
What is the consequence of removing the peptidoglycan layer from a gram-positive bacterium?
The bacterium lyses due to osmotic pressure
Study Notes
Gram-Positive Bacteria
- A gram-positive bacterium has a thick, multilayered cell wall consisting mainly of peptidoglycan (150 to 500 Å) surrounding the cytoplasmic membrane.
- The peptidoglycan is a meshlike exoskeleton that allows diffusion of metabolites to the plasma membrane.
- The peptidoglycan is essential for structure, replication, and survival in hostile conditions.
- Lysozyme, an enzyme found in human tears and mucus, can degrade peptidoglycan, leading to bacterial lysis.
- The gram-positive cell wall may include other components such as proteins, teichoic and lipoteichoic acids, and complex polysaccharides.
- Virulence proteins, such as the M protein of streptococci and protein A of S. aureus, are covalently bound to the peptidoglycan.
- Teichoic acids are water-soluble anionic polymers of polyol phosphates that are covalently linked to the peptidoglycan and essential to cell viability.
- Lipoteichoic acids have a fatty acid and are anchored in the cytoplasmic membrane.
Gram-Negative Bacteria
- Gram-negative cell walls are more complex than gram-positive cell walls, both structurally and chemically.
- The gram-negative cell wall contains a thin peptidoglycan layer (5-10% of the cell wall by weight) and an outer membrane.
- There are no teichoic or lipoteichoic acids in the gram-negative cell wall.
- The outer membrane contains a periplasmic space with transport systems for iron, proteins, sugars, and other metabolites, as well as hydrolytic enzymes.
- The periplasmic space contains virulence factors such as collagenases, hyaluronidases, proteases, and β-lactamase in pathogenic gram-negative species.
- The gram-negative cell wall also contains type I to V secretion devices that provide mechanisms for the uptake and release of different metabolites and other compounds.
This quiz covers the characteristics of gram-positive bacteria, including their cell wall structure, and microbiomes. Learn about the peptidoglycan layer and its functions.
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