<P> Peptidoglycan, also known as murein, is a polymer consisting of sugars and amino acids that forms a mesh - like layer outside the plasma membrane of most bacteria, forming the cell wall . The sugar component consists of alternating residues of β - (1, 4) linked N - acetylglucosamine (NAG) and N - acetylmuramic acid (NAM). Attached to the N - acetylmuramic acid is a peptide chain of three to five amino acids . The peptide chain can be cross-linked to the peptide chain of another strand forming the 3D mesh - like layer . Peptidoglycan serves a structural role in the bacterial cell wall, giving structural strength, as well as counteracting the osmotic pressure of the cytoplasm . A common misconception is that peptidoglycan gives the cell its shape; however, whereas peptidoglycan helps maintain the structural strength of the cell, it is actually the MreB protein that facilitates cell shape . Peptidoglycan is also involved in binary fission during bacterial cell reproduction . </P> <P> The peptidoglycan layer is substantially thicker in gram - positive bacteria (20 to 80 nanometers) than in gram - negative bacteria (7 to 8 nanometers), with the attachment of the S - layer . Peptidoglycan forms around 90% of the dry weight of gram - positive bacteria but only 10% of gram - negative strains . Thus, presence of high levels of peptidoglycan is the primary determinant of the characterisation of bacteria as gram - positive . In gram - positive strains, it is important in attachment roles and serotyping purposes . For both gram - positive and gram - negative bacteria, particles of approximately 2 nm can pass through the peptidoglycan . </P>

Where is peptidoglycan found in a bacterial cell