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4.4F: Damage of the Cell Wall

  • Page ID
    8848
  • [ "article:topic", "authorname:boundless" ]

    The cell wall is responsible for bacterial cell survival and protection against environmental factors and antimicrobial stress.

    LEARNING OBJECTIVES

    Discuss the effects that damage to the cell wall has on the bacterial cell

    KEY TAKEAWAYS

    Key Points

    • Gram-positive and Gram-negative bacteria are protected by an external cell wall composed of varying layers of peptidoglycan.
    • Damage to bacterial cell wall compromises its integrity and creates imbalance of electrolytes that trigger cell death.
    • Some antibiotic classes act by inhibiting the synthesis of cell wall building blocks leading to cell lysis and death.

    Key Terms

    • hydrolase: An enzyme that catalyzes the hydrolysis of a substrate.
    • transpeptidase: Any enzyme that catalyzes the transfer of an amino or peptide group from one molecule to another

    The cell wall is the principal stress-bearing and shape-maintaining element in bacteria. Its integrity is thus of critical importance to the viability of a particular cell. In both gram-positive and gram-negative bacteria, the scaffold of the cell wall consists of a cross-linked polymer peptidoglycan. The cell wall of gram-negative bacteria is thin (approximately only 10 nanometers in thickness), and is typically comprised of only two to five layers of peptidoglycan, depending on the growth stage. In gram-positive bacteria, the cell wall is much thicker (20 to 40 nanometers thick).

    While the peptidoglycan provides the structural framework of the cell wall, teichoic acids, which make up roughly 50% of the cell wall material, are thought to control the overall surface charge of the wall. This affects murein hydrolase activity, resistance to antibacterial peptides, and adherence to surfaces. Although both of these molecules are polymerized on the surface of the cytoplasmic membrane, their precursors are assembled in the cytoplasm. Any event that interferes with the assembling of the peptidoglycan precursor, and the transport of that object across the cell membrane, where it will integrate into the cell wall, would compromise the integrity of the wall. Damage to the cell wall disturbs the state of cell electrolytes, which can activate death pathways (apoptosis or programmed cell death). Regulated cell death and lysis in bacteria plays an important role in certain developmental processes, such as competence and biofilm development. They also play an important role in the elimination of damaged cells, such as those irreversibly injured by environmental or antibiotic stress. An example of an antibiotic that interferes with bacterial cell wall synthesis is Penicillin. Penicillin acts by binding to transpeptidases and inhibiting the cross-linking of peptidoglycan subunits. A bacterial cell with a damaged cell wall cannot undergo binary fission and is thus certain to die.

    image

    Penicillin mechanism of action: Penicillin acts by binding to penicillin binding proteins and inhibiting the cross-linking of peptidoglycan subunits.

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