N-acetylmuramic acid (MurNAc) is a bacterial cell wall component. Peptidoglycan, also called murein, is a polymer that consists of long glycan chains that are cross-linked via flexible peptide bridges to form a strong but elastic structure that protects the underlying protoplast from lysing due to the high internal osmotic pressure. The peptidoglycan is the only cell wall polymer common to both gram-negative and gram-positive bacteria. The glycan chain is built up of alternating, β-1,4-linked N-acetylglucosamine (GlcNAc) and N-acetylmuramic acid (MurNAc) subunits. The chemistry of the glycan chains varies only slightly between different bacteria.