The Gram-negative bacterial cell wall consists of three primary layers.
Figure 1. Upper image. Gram-negative bacterial cell wall. Lower image. Lipopolysaccharide
Cytoplasmic membrane: Surrounds the cytoplasm of Gram-positive and Gram-negative bacteria and regulates the passage of molecules in and out of the bacteria. It is similar to the one found in the mammalian cell membrane and consists mainly of proteins and lipids. Peptidoglycan: The peptidoglycan of the Gram-negative cell wall is a thin (5-10 nm) mesh of repeating subunits containing sugars and amino acids.
The Periplasmic space: lies between the outer membrane and the cytoplasmic membrane. It consists of a gel-like matrix containing a wide variety of proteins that are important for various cell functions.
The outer membrane protects the bacteria and acts as a barrier towards certain antibiotics. In the outer membrane, we find:
- Porin proteins penetrate the outer membrane of Gram-negative bacteria, forming pores which allow passive diffusion of hydrophilic molecules between the bacteria and the exterior
- Lipopolysaccharides are specific to the outer leaflet of the outer membrane. They carry a negative charge, which contributes to maintaining the shape of the bacteria.
Lipopolysaccharides are notorious because they have the potential of causing toxic shock in the infected host.