Gram positive

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The Gram-positive bacterial cell wall is one of the two types of bacterial cell walls the other being Gram-negative cell walls. The Gram-positive cell walls are mainly composed of peptidoglycan although they also consist of the surface proteins, teichoic and lipoteichoic acids the latter of which connects the cell wall to the cell membrane. The teichoic and lipoteichoic acids contribute to the positive charge of the bacterial cell surface and they are glycerophosphate or ribitol phosphate- containing acidic polysaccharides.

The thick layer of peptidoglycan enables the cell wall to retain the purple colour of crystal violet upon constriction consequent upon treatment with iodine. Thus Gram-positive bacterial cell walls stain purple.

Examples of Gram-positive bacteria include Staphylococcus aureus, Streptococcus pyogenes and Streptococcus pneumonia amongst others[1].

The structure of the Gram-positive peptidoglycan cell wall

Peptidoglycan is made from monomers called glycan tetrapeptides, these are linked together in chains which are in turn linked together. In gram-positive bacteria the crosslink is a peptide interbridge which is different in its structure depending on the bacterial strain, in Staphylococcus aureus the interbridge is made from five glycine residues[2].

References

  1. Kaiser, G. (2012) The Prokaryotic Cell: Bacteria. http://faculty.ccbcmd.edu/courses/bio141/lecguide/unit1/prostruct/gpcw.html. The Community College of Baltimore County.
  2. Madigan Micahel T, Martinko John M, Bender Kelly S, Buckley Daniel H, Stahl David A. “Brock biology of microorganisms” 14th edition, Pearson education limited, 2014.
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