ABSTRACT
The single most important characteristic which distinguishes mycoplasmas from all other prokaryotes is their complete lack of a cell wall. Demonstration of a single membrane in cell sections has become essential to define a new isolate as a mycoplasma. Thin sections of mycoplasmas reveal an extremely simple ultrastructure consisting of a plasma membrane, ribosomes, and a prokaryotic nucleoid. The lack of a cell wall in mycoplasmas facilitates the isolation of their cytoplasmic membranes by eliminating the need for the tedious procedures usually involved in the separation of the bacterial cell wall from the cytoplasmic membrane. Isolated mycoplasma membranes resemble plasma membranes of other prokaryotes in gross chemical composition, being composed mainly of proteins and lipids. The fatty acid residues of membrane phospholipids and glycolipids constitute the major portion of the hydrophobic core of the membrane, so that the physical properties of this core are largely determined by the composition of these residues.
