A structure forming a layer external to the plasma membrane. It controls the shape of the bacterium and serves as a permeability barrier. In some species a capsule may be formed external to the cell wall. The walls of Gram-positive bacteria are 30–100 nm thick and appear homogeneous. They are composed mainly of peptidoglycans. Gram-negative cell walls are thinner (20–30 nm) and are layered. The inner layer (adjacent to the plasma membrane) contains peptidoglycans. The outer layer contains peptidoglycans cross-linked to lipoproteins. Certain bacteria lack cell walls. See Gram-staining procedure, Mycoplasma, peptidoglycan.
Subjects: Medicine and Health — Genetics and Genomics.