Cell wall is the second layer of the cell envelope below the glycocalyx. This layer gives bacteria their characteristic shape and also provides strong structural support to prevent a bacterium from bursting or collapsing in a hypotonic solution.
Peptidoglycan, also known as murein, is the single most important component of the bacterial cell wall. It is a polymer that exists as one immense, covalently linked molecule. It forms a supporting net around a bacterium that resembles multiple layers of chain-link fence.
In the peptidoglycan polymer, molecules of N-acetylglucosamine alternate with molecules of N-acetylmuramic acid. These molecules are cross-linked by short peptide chains to provide a strong but flexible support framework.