outer membrane

Definition

Target type: cellularcomponent

The external membrane of Gram-negative bacteria or certain organelles such as mitochondria and chloroplasts; freely permeable to most ions and metabolites. [GOC:go_curators]

The outer membrane is a unique feature of Gram-negative bacteria. It is a phospholipid bilayer, like the inner membrane, but it also contains a distinctive outer leaflet composed of lipopolysaccharide (LPS). LPS is a complex molecule with three main components: lipid A, core oligosaccharide, and O-antigen. Lipid A is embedded in the outer membrane and acts as an endotoxin, triggering an immune response in the host. The core oligosaccharide is a short sugar chain that connects lipid A to the O-antigen. The O-antigen is a long, repeating sugar chain that extends outwards from the cell surface and varies between bacterial species.

In addition to LPS, the outer membrane also contains a variety of proteins, including porins and lipoproteins. Porins are transmembrane proteins that form channels through the outer membrane, allowing the passage of small molecules, such as nutrients and waste products. Lipoproteins are anchored to the outer membrane by a lipid molecule and play a variety of roles, including attachment to host cells, transport of molecules across the membrane, and regulation of gene expression.

The outer membrane provides a protective barrier for Gram-negative bacteria, preventing the entry of harmful substances and facilitating the export of toxins and other virulence factors. It also plays a crucial role in the interaction of bacteria with their environment, including their attachment to surfaces, their resistance to antibiotics, and their ability to cause disease.'
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Proteins (1)

Compounds (2)