Prokaryotic Cell Structure
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Questions and Answers

What happens to the pores in the cell walls of gram-positive bacteria when treated with alcohol?

  • They disappear
  • They close (correct)
  • They remain unchanged
  • They become larger

    • What happens to the crystal violet-iodine complex in gram-negative bacteria after alcohol treatment?

  • It is extracted from the cell (correct)
  • It remains in the cell
  • It changes color
  • It becomes insoluble

    • What is the function of the outer membrane in gram-negative bacteria?

  • To regulate temperature
  • To keep proteins inside the cell
  • To control pH
  • To keep proteins outside the cell (correct)

    • What is the periplasm?

    <p>The region between the outer and cytoplastic membranes</p> Signup and view all the answers

    What is the consistency of the periplasm contents?

    <p>Gel-like</p> Signup and view all the answers

    What type of molecules are not permeable through the outer membrane?

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

    What is the function of glycocalyx?

    <p>To protect the cell and adhere to surfaces</p> Signup and view all the answers

    What is a capsule?

    <p>A dense, tightly bound glycocalyx</p> Signup and view all the answers

    What percentage of the total cell wall of gram-negative bacteria consists of peptidoglycan?

    <p>10%</p> Signup and view all the answers

    What is the function of porins in the outer membrane of gram-negative bacteria?

    <p>To form channels for the entrance and exit of hydrophilic low-molecular-weight substances</p> Signup and view all the answers

    What is the term for the toxic component of LPS?

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

    What is responsible for the differences in the Gram stain reaction between gram-positive and gram-negative bacteria?

    <p>The structural differences between the cell walls</p> Signup and view all the answers

    What is the other name for the outer membrane of gram-negative bacteria?

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

    What is the purpose of the Gram stain?

    <p>To distinguish between gram-positive and gram-negative bacteria</p> Signup and view all the answers

    What is the name of the polysaccharide portion of LPS?

    <p>Both A and B</p> Signup and view all the answers

    What is the consequence of the structural differences between the cell walls of gram-positive and gram-negative bacteria in the Gram stain reaction?

    <p>The complex is not extracted by alcohol from gram-negative bacteria</p> Signup and view all the answers

    What is the primary function of the cell envelope in prokaryotic cells?

    <p>To protect the cell from its environment</p> Signup and view all the answers

    What is the structure of the plasma membrane?

    <p>Phospholipid bilayer with embedded proteins</p> Signup and view all the answers

    What is the selective barrier function of the plasma membrane?

    <p>To control the movement of molecules into and out of the cell</p> Signup and view all the answers

    What is the role of the cell wall in bacterial cells?

    <p>To provide structural support and maintain cell shape</p> Signup and view all the answers

    What is the main component of the cell wall in most bacteria?

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

    What is the function of peripheral proteins in the plasma membrane?

    <p>To facilitate the transport of molecules into the cell</p> Signup and view all the answers

    What is the function of lysozyme in animal secretions?

    <p>To break down peptidoglycan</p> Signup and view all the answers

    What is the function of electron transport in bacterial respiration?

    <p>To generate ATP</p> Signup and view all the answers

    What is the percentage of peptidoglycan in the cell wall of gram-positive bacteria?

    <p>90%</p> Signup and view all the answers

    What is the role of the cell wall in some species of bacteria causing disease?

    <p>It contributes to the ability of some species to cause disease</p> Signup and view all the answers

    What is the chemical composition of the cell wall used for?

    <p>To differentiate major types of bacteria</p> Signup and view all the answers

    What is the function of teichoic acids in the cell wall?

    <p>To bind Ca2+ and Mg2+ for transport into the cell</p> Signup and view all the answers

    What is the result of lysozyme breaking down peptidoglycan?

    <p>The cell wall becomes weaker</p> Signup and view all the answers

    What is the structure of peptidoglycan?

    <p>A mesh-like layer of sugars and amino acids</p> Signup and view all the answers

    What happens to the cell when the cell wall is weakened by lysozyme?

    <p>The cell swells and eventually bursts</p> Signup and view all the answers

    What is the charge of the cell surface due to teichoic acids?

    <p>Negatively charged</p> Signup and view all the answers

    Study Notes

    Cell Envelope

    • The cell envelope is the boundary layer of bacteria, lying outside the cytoplasm
    • It has a structure comprising a cell wall and a cytoplasmic membrane
    • Gram-positive bacteria have a two-layer cell envelope, while Gram-negative bacteria have a three-layer cell envelope

    Plasma (Cell) Membrane

    • A barrier that separates the cell from its environment
    • Composed of a phospholipid bilayer with embedded proteins
    • Has an inner and outer hydrophilic face, and a hydrophobic interior, forming a barrier to hydrophilic molecules
    • Functions:
      • Protects the cytoplasm and inner structure of the cell
      • Acts as a selective barrier for material entering and exiting the cell
      • Important for nutrient breakdown, energy production, and bacterial respiration
      • Involved in chromosomal segregation during replication

    Cell Wall of Bacteria

    • Responsible for the shape of the cell
    • Protects the interior structure of the cell from environmental changes
    • Prevents bacterial cells from rupturing due to osmotic pressure
    • Contributes to disease causation in some species
    • Site of action for some antibiotics
    • Cell wall structure is used to differentiate major types of bacteria
    • Peptidoglycan (murein) is a key component of the cell wall

    Peptidoglycan (Murein)

    • A polymer consisting of sugars and amino acids
    • Forms a mesh-like layer outside the cell membrane
    • Composed of alternating residues of β-(1,4) linked N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM)
    • Subunits are covalently joined to form glycan chains
    • Can be destroyed by certain agents, such as lysozyme
    • Lysozyme breaks the β-1,4-glycosidic bonds between NAG and NAM, weakening the wall and leading to cell lysis

    Gram-Positive Cell Wall

    • In Gram-positive bacteria, the cell wall consists of multiple layers of peptidoglycan
    • Teichoic acids are embedded in the cell wall, giving it a negative charge
    • Teichoic acids bind Ca2+ and Mg2+ for transport into the cell

    Gram-Negative Cell Wall

    • In Gram-negative bacteria, the cell wall consists of a thin layer of peptidoglycan
    • The outer membrane is composed of a lipopolysaccharide layer, with a complex of lipid and polysaccharide
    • The lipopolysaccharide layer is toxic and responsible for the pathogenicity of Gram-negative bacteria
    • Porins are proteins in the outer membrane that function as channels for hydrophilic substances

    Periplasm

    • A region between the outer surface of the cytoplasmic membrane and the inner surface of the outer membrane
    • Contains proteins, including hydrolytic enzymes, binding proteins, and chemoreceptors
    • Proteins in the periplasm are involved in initial food molecule degradation, substrate transport, and chemotaxis response

    Glycocalyx

    • A coating of repeating polysaccharide, protein, or both
    • Protects the cell and helps with attachment to the environment
    • Can form a loose shield (slime layer) or a dense layer (capsule)
    • Involved in protection, attachment, and biofilm formation

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    Description

    This quiz covers the structure of a prokaryotic cell, including the cell envelope, plasma membrane, and differences between gram-positive and gram-negative bacteria.

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