The peptidoglycan (murein) sacculus is a crucial component of the bacterial cell wall, providing structural integrity and shape. It consists of glycan strands cross-linked by short peptides, forming a closed, bag-shaped structure surrounding the cytoplasmic membrane. The composition and sequence of peptides vary among different bacterial species, and the fine structure can change with growth conditions. Limited biophysical data suggest that peptidoglycan has a thickness, elasticity, and porosity that allow it to withstand turgor pressure while allowing diffusion of large molecules. The architecture of peptidoglycan is complex, with variations in cross-linking and interpeptide bridges, and the degree of cross-linking can vary significantly between species. The fine structure of peptidoglycan, including the composition and distribution of muropeptides, can be modified by growth conditions and environmental factors, and these changes are associated with bacterial pathogenesis. Peptidoglycan's biophysical properties, such as thickness, elasticity, and porosity, are influenced by factors like pH and osmotic pressure, and these properties are essential for understanding the cell's response to environmental changes. Despite extensive research, the exact structure and architecture of peptidoglycan remain challenging to fully elucidate, particularly in Gram-negative bacteria.The peptidoglycan (murein) sacculus is a crucial component of the bacterial cell wall, providing structural integrity and shape. It consists of glycan strands cross-linked by short peptides, forming a closed, bag-shaped structure surrounding the cytoplasmic membrane. The composition and sequence of peptides vary among different bacterial species, and the fine structure can change with growth conditions. Limited biophysical data suggest that peptidoglycan has a thickness, elasticity, and porosity that allow it to withstand turgor pressure while allowing diffusion of large molecules. The architecture of peptidoglycan is complex, with variations in cross-linking and interpeptide bridges, and the degree of cross-linking can vary significantly between species. The fine structure of peptidoglycan, including the composition and distribution of muropeptides, can be modified by growth conditions and environmental factors, and these changes are associated with bacterial pathogenesis. Peptidoglycan's biophysical properties, such as thickness, elasticity, and porosity, are influenced by factors like pH and osmotic pressure, and these properties are essential for understanding the cell's response to environmental changes. Despite extensive research, the exact structure and architecture of peptidoglycan remain challenging to fully elucidate, particularly in Gram-negative bacteria.