peptidoglycan

Examples of peptidoglycan in the following topics:

• Peptidoglycan Synthesis and Cell Division

  • Peptidoglycan, also known as murein, is a polymer and consists of sugars and amino acids which form the cell walls of bacteria.
  • A common misconception is that peptidoglycan gives the cell its shape.
  • Peptidoglycan is also involved in binary fission during bacterial cell reproduction.
  • Peptidoglycan forms around 90% of the dry weight of Gram-positive bacteria but only 10% of Gram-negative strains.
  • For both Gram-positive and Gram-negative bacteria, particles of approximately 2 nm can pass through the peptidoglycan.

• The Cell Wall of Bacteria

  • Bacteria are protected by a rigid cell wall composed of peptidoglycans.
  • The major component of the bacterial cell wall is peptidoglycan or murein.
  • This rigid structure of peptidoglycan, specific only to prokaryotes, gives the cell shape and surrounds the cytoplasmic membrane.
  • Peptidoglycan is a huge polymer of disaccharides (glycan) cross-linked by short chains of identical amino acids (peptides) monomers.
  • From the peptidoglycan inwards all bacterial cells are very similar.

• Damage to the Cell Wall

  • 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.
  • 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.
  • Penicillin acts by binding to transpeptidases and inhibiting the cross-linking of peptidoglycan subunits.
  • Penicillin acts by binding to penicillin binding proteins and inhibiting the cross-linking of peptidoglycan subunits.

• Gram-Positive Cell Envelope

  • Gram-positive bacteria have cell envelopes made of a thick layer of peptidoglycans.
  • Primarily, it detects peptidoglycan, which is present in a thick layer in Gram-positive bacteria.
  • In Gram-positive bacteria, the cell wall is thick (15-80 nanometers), and consists of several layers of peptidoglycan.
  • Running perpendicular to the peptidoglycan sheets is a group of molecules called teichoic acids, which are unique to the Gram-positive cell wall.
  • One idea is that they provide a channel of regularly-oriented, negative charges for threading positively-charged substances through the complicated peptidoglycan network.

• Inhibiting Cell Wall Synthesis

  • Antibiotics commonly target bacterial cell wall formation (of which peptidoglycan is an important component) because animal cells do not have cell walls.
  • The peptidoglycan layer is important for cell wall structural integrity, being the outermost and primary component of the wall.
  • The final step in the synthesis of the peptidoglycan is facilitated by penicillin-binding proteins (PBPs).
  • This class of drugs inhibit the synthesis of cell walls in susceptible microbes by inhibiting peptidoglycan synthesis.
  • They bind to the amino acids within the cell wall preventing the addition of new units to the peptidoglycan .

• Diverse Cell Forms of Methanogens

  • The cell walls of of Methanogens, like other Archaea, lack peptidoglycan, a polymer found in the cell walls of the bacteria.
  • Pseudopeptidoglycan differs in chemical structure from bacterial peptidoglycan, but resembles eubacterial peptidoglycan in morphology, function, and physical structure.
  • These differences makes these archaea resistant to the enzyme, lysozyme, which only breaks down β (1,4) sugar linkages like those found in peptidoglycan.

• Gram-Negative Outer Membrane

  • In the Gram-negative Bacteria the cell wall is composed of a single layer of peptidoglycan surrounded by a membranous structure called the outer membrane.
  • The peptidoglycan layer is non-covalently anchored to lipoprotein molecules called Braun's lipoproteins through their hydrophobic head.
  • Together, the plasma membrane and the cell wall (outer membrane, peptidoglycan layer, and periplasm) constitute the gram-negative envelope.

• Cell Walls of Archaea

  • Archaeal cell walls differ from bacterial cell walls in their chemical composition and lack of peptidoglycans.
  • For instance, the cell walls of all bacteria contain the chemical peptidoglycan.

• MreB and Determinants of Cell Morphology

  • Therefore, MreB probably directs the synthesis and insertion of new peptidoglycan building units into the existing peptidoglycan layer to allow length growth of the bacteria.
  • Recent research shows that peptidoglycan precursors are inserted into cell wall following helical pattern which is dependent on MreB, and it's reported that MreB also promote the GT activity of PBPs.
  • MreB- RodZ complexes act as a major stabilizing factor in bacterial cell wall and ensure the insertion of new peptidoglycan in a spiral like fashion into the cell wall.

• Basic Structures of Prokaryotic Cells

  • Bacterial cell walls contain peptidoglycan composed of polysaccharide chains that are cross-linked by unusual peptides containing both L- and D-amino acids, including D-glutamic acid and D-alanine.
  • There are more than 100 different forms of peptidoglycan.
  • Up to 90 percent of the cell wall in gram-positive bacteria is composed of peptidoglycan, with most of the rest composed of acidic substances called teichoic acids.
  • Gram-negative bacteria have a relatively thin cell wall composed of a few layers of peptidoglycan (only 10 percent of the total cell wall), surrounded by an outer envelope containing lipopolysaccharides (LPS) and lipoproteins.
  • Both groups have a cell wall composed of peptidoglycan: in gram-positive bacteria, the wall is thick, whereas in gram-negative bacteria, the wall is thin.