Bacterial Cell Wall Structure
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Questions and Answers

What is the primary function of the bacterial cell wall?

  • Generate energy for the cell
  • Act as a storage site for nutrients
  • Facilitate the movement of molecules
  • Provide structural support and protection (correct)

    • Which process expends ATP to transport molecules against their gradient?

  • Simple diffusion
  • Protein synthesis
  • Group translocation (correct)
  • Endocytosis

    • In the context of ion gradients, what serves to store energy for metabolism or drive transport of other molecules?

  • Proton pumps (correct)
  • ABC transporters
  • Ribosomes
  • Cell walls

    • Which bacterial taxonomic group is characterized by having a Gram-positive cell envelope?

    <p>Firmicutes</p> Signup and view all the answers

    What is the function of the murein lipoprotein in Gram-negative bacteria?

    <p>Links the cell wall to the outer membrane</p> Signup and view all the answers

    What is the main component of the bacterial cell wall that provides its structure?

    <p>Peptidoglycan</p> Signup and view all the answers

    How do membrane-permeant weak acids affect the internal pH of a cell?

    <p>Cause a drop in pH</p> Signup and view all the answers

    What is the composition of the outer membrane in Gram-negative bacteria?

    <p>Inward- /outer-facing leaflets differ in lipid composition</p> Signup and view all the answers

    Which structure in Gram-negative bacteria acts as an endotoxin when the cell dies?

    <p>Lipopolysaccharide layer</p> Signup and view all the answers

    Where is the periplasm located in a bacterial cell?

    <p>Between the inner membrane &amp; outer membrane</p> Signup and view all the answers

    Which bacteria have a cell wall comprised of pseudomurien?

    <p>Archaea</p> Signup and view all the answers

    What is the function of a bacterial capsule?

    <p>Forms a protective layer outside the cell envelope</p> Signup and view all the answers

    What is the main difference between capsules and slime layers in bacteria?

    <p>Capsules are more tightly associated with the cell than slime layers.</p> Signup and view all the answers

    What is the main characteristic of biofilms?

    <p>They are multi-cell populations surrounded by an exopolysaccharide matrix.</p> Signup and view all the answers

    What is the main component of peptidoglycan in bacterial cell walls?

    <p>Carbohydrates</p> Signup and view all the answers

    Which antibiotic specifically targets the synthesis of peptidoglycan in bacteria?

    <p>Penicillin</p> Signup and view all the answers

    Which type of bacteria has a more complex cell envelope, Gram-positive or Gram-negative?

    <p>Gram-negative</p> Signup and view all the answers

    What is the function of ion gradients and membrane-permeant weak acids/bases in prokaryotic cells?

    <p>Maintaining osmotic balance</p> Signup and view all the answers

    Which antibiotics have an effect on peptidoglycan synthesis in bacterial cells?

    <p>Penicillin and vancomycin</p> Signup and view all the answers

    How do Gram-negative bacterial envelopes differ from Gram-positive bacterial envelopes?

    <p>Gram-negative envelopes have an inner and outer membrane</p> Signup and view all the answers

    Which of the following is a key difference in cell envelope composition between Archaea and Mycoplasma?

    <p>Mycoplasma has no cell wall</p> Signup and view all the answers

    What are ABC transporters responsible for in prokaryotic cells?

    <p>Active transport of molecules against their concentration gradient</p> Signup and view all the answers

    Which external structures to the cell envelope play a role in adhesion to surfaces?

    <p>Flagella and pili</p> Signup and view all the answers

    What is the main component of a bacterial cell wall structure?

    <p>Peptidoglycan</p> Signup and view all the answers

    Which enzyme is targeted by penicillin to prevent cell wall synthesis?

    <p>Beta-lactamase</p> Signup and view all the answers

    What is the role of vancomycin in bacterial cell wall synthesis?

    <p>Prevents cross-bridging by binding to terminal alanine dipeptide</p> Signup and view all the answers

    What is the function of MreB in rod-shaped bacterial cells?

    <p>Directs the helical direction of peptidoglycan synthesis</p> Signup and view all the answers

    Which bacterial species have cell wall synthesis occurring only at the midpoint of fission?

    <p>Streptococcus and Staphylococcus</p> Signup and view all the answers

    What type of bacteria have thick cell walls with multiple peptidoglycan layers penetrated with teichoic acids?

    <p>Firmicutes</p> Signup and view all the answers

    Study Notes

    Prokaryote Cell Structure and Function

    • Prokaryote cell composition: a cell envelope, protected by one or more structural support layers, including a cell wall, S-layer, outer membrane, and complex layers (e.g., mycobacterial species).

    Cell Membrane Structure

    • Prokaryote cell membranes are composed of different lipid types, including bacterial and archaeal membrane lipids.
    • Transport processes: passive (osmosis) and active (requiring energy to move molecules against their gradient).
    • Ion gradients: store energy for metabolism or drive transport of other molecules.
    • Membrane-permeant weak acids/bases: small, neutral molecules that can diffuse into the cell and affect internal pH.

    Active Transport

    • Requires energy to move molecules against their gradient.
    • Mechanisms: ABC transporters (e.g., amino acid, carbohydrate transport) and group translocation (modification of substrate during transport).

    Cell Envelope

    • Refers to the chemical structure external to the inner membrane.
    • Composed of peptidoglycan (murein), a polymer of disaccharides cross-linked with peptide tetramers.

    Peptidoglycan Synthesis

    • Involves many enzymes, including penicillin-binding proteins.
    • Penicillin targets the enzyme that cross-links peptides, while vancomycin binds to the terminal alanine dipeptide, preventing cross-bridging.
    • Bacterial resistance mechanisms: beta-lactamase (cleaves penicillin) and vancomycin resistance.

    Cell Envelopes of Gram-positive and Gram-negative Bacteria

    • Gram-positive bacteria: thick cell wall, multiple peptidoglycan layers penetrated with teichoic acids.
    • Gram-negative bacteria: thin cell wall, 1-2 peptidoglycan layers, bridged to outer membrane via the murein lipoprotein.

    Outer Membrane of Gram-negative Bacteria

    • Lipopolysaccharide (LPS) layer: an endotoxin released when the cell dies.
    • Outer membrane proteins: non-specific porins that transport sugars, peptides.
    • Lipid A: short chain fatty acids linked to glucosamine dimers.

    Atypical Cell Walls

    • Mycoplasma: smallest bacteria, lack cell wall.
    • Archaea: cell wall is comprised of pseudomurien.
    • Mycobacteria: contain waxy lipids (mycolic acids) in addition to peptidoglycan.

    Structures External to the Cell Envelope

    • Capsule: a polysaccharide layer that lies outside the cell envelope, can be protein in nature.
    • Slime layer: a looser assemblage of polysaccharides.
    • Biofilm: a multi-cell population surrounded by an exopolysaccharide matrix.

    Comparison of Cell Envelopes

    • Gram-positive vs. Gram-negative bacteria: differences in cell wall composition and structure.
    • Archaea and Mycoplasma: unique cell envelope compositions.
    • Mycobacterial cell envelope: contains waxy lipids (mycolic acids) in addition to peptidoglycan.

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    Description

    Learn about the structure of a bacterial cell wall, including its composition, functions, and the enzymes involved in cell wall synthesis. Explore how antibiotics like penicillin and vancomycin target specific enzymes in the cell wall.

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