It is common knowledge that Gram-negative bacteria possess an internal membrane and an outer membrane, which contains lipopolysaccharide (LPS), as well as a periplasm that contains peptidoglycan.
But how are these structures actually arranged?
In this picture, for instance, it looks like the whole periplasm is filled with peptidoglycan:
https://hotcore.info/act/kareff-092024p.html
while in this one, there is an additional space:
https://quizlet.com/372741280/structures-of-grampositive-and-gramnegativebacterial-cell-walls-diagram/
Also, is the outer lipid leaflet of the outer membrane composed of phospholipids like the inner leaflet, with LPS embedded into it, or are the two leaflets chemically different?
Thank you
Dear Dr. Luigi Marongiu
Is the outer lipid leaflet of the outer membrane composed of phospholipids like the inner leaflet, with LPS embedded into it, or are the two leaflets chemically different?
The outer membrane of Gram-negative bacteria is composed of a unique bilayer structure containing lipopolysaccharides (LPS) in its outer leaflet and phospholipids in its inner leaflet. LPS contains a lipid A domain that can act as a virulence factor, triggering immune responses in animals. The phospholipids found in the inner leaflet of the outer membrane, provides structural support and acts as a boundary. Thus, the outer membrane is a bilayer structure, like a typical cell membrane but with a chemically asymmetric arrangement. This asymmetric arrangement, with LPS on the outside and phospholipids on the inside, is crucial for the outer membrane's function.
In this picture, for instance, it looks like the whole periplasm is filled with peptidoglycan.
No, the entire periplasm is not filled with peptidoglycan. The peptidoglycan forms a distinct, rigid layer embedded within this protein-rich space, rather than completely filling it.
while in this one, there is an additional space..
The additional space is the periplasmic space which is a compartment in Gram-negative bacteria, situated between the inner cytoplasmic membrane and the outer membrane. It is filled with a gel-like matrix called the periplasm, which contains a variety of enzymes and proteins involved in cell wall synthesis, protein folding, nutrient acquisition, and waste degradation. As mentioned above, the periplasmic space contains peptidoglycan, which is a rigid layer of crosslinked sugars and amino acids embedded within the periplasm. This peptidoglycan layer is crucial for maintaining the structural integrity of the cell wall.
Regards,
Malcolm Nobre
The figures you referring were just a schematic, which showing periplasm contain full of peptidoglycan, but actually not like that. The periplasm is a true aqueous compartment that contains a thin peptidoglycan layer plus proteins, not just “all peptidoglycan".The outer membrane is chemically asymmetric, with phospholipids on the inner leaflet and LPS dominating the outer leaflet.
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