Generally the cell membrane of bacteria is similar to the familiar bileaflet membrane, containing phospholipids and proteins, that is found throughout the living world. However, there are important differences. The bacterial cell membrane is exceptionally rich in proteins (up to 70% of its weight) and does not (except in the case of mycoplas-mas) contain sterols. The bacterial chromosome is attached to the cell membrane, which plays a role in segregation of daughter chromosomes at cell division, analogous to the role of the mitotic apparatus of eukaryotes. The membrane is the site of synthesis of DNA, cell wall polymers, and membrane lipids. It contains the entire electron trans-port system of the cell (and, hence, is functionally analogous to the mitochondria of eukaryotes). It contains receptor proteins that function in chemotaxis. Like cell mem-branes of eukaryotes, it is a permeability barrier and contains proteins involved in se-lective and active transport of solutes. It is also involved in secretion to the exterior of proteins (exoproteins), including exotoxins and hydrolytic enzymes involved in the pathogenesis of disease. The bacterial cell membrane is therefore the functional equiva-lent of most of the organelles of the eukaryotic cell and is vital to the growth and maintenance of the cell.
The cell membranes of Gram-positive and Gram-negative cells are similar in compo-sition, structure, and function except for the modification, already described, in Gram-negative cells that places the outer membrane of the wall and the cell membrane in intimate contact (Bayer’s junctions).