Bacterial outer membrane

The outer membrane of Gram - negative bacteria occurs mainly in proteobacteria and cyanobacteria. It is part of a two bilayers membrane system. The inner membrane is in this case always defined by the actual cell membrane, while the outer membrane acts as an additional separation from the outside. Both membranes include a cellular compartment, which is referred to as the periplasmic space.

The two layers of the Outer membrane are constructed differently. The composition of the inner layer is similar to a unit of the membrane. It mainly consists of phospholipids, are embedded in the lipoproteins. This lipoprotein complex maintains a connection to the cell wall in the periplasmic space. The composition of the outer layer, however, differs significantly from that of a biological membrane unit: phospholipids are largely replaced by polysaccharides, lipids to form the complex lipopolysaccharide (LPS). Together with numerous proteins form the major components of the outer layer. The outer membrane which, unlike the interior membrane as " not energized " for biochemical processes so there is no energy in the form of ATP and no proton gradient is available. The exact composition of the membrane is usually highly variable and plays an important role in the adaptability of bacteria to changing environmental conditions (eg changes in osmolarity ) and the pathogenicity of individual strains. The lipopolysaccharides act as strong antigens, pyrogens and endotoxins.

The outer membrane is primarily used as a diffusion barrier for large molecules. As a "filter " it prevents biopolymers from entering the periplasmic space, but most of all it prevents the escape of proteins and enzymes from the periplasm into the environment. In the membrane are numerous porins and other integral proteins that are required for transport processes or the receiving signals and environmental stimuli. Characteristic of integral proteins of the Outer membrane β -barrel are barrel-shaped structures. Parts of the anchoring of flagella and cilia ( the so-called L-ring ) are located in the exterior membrane.

• Microbiology