According to Scientific American, peptidoglycan is the substance that makes up the cell walls of bacteria. The polymer is primarily composed of amino acids and sugars. Peptidoglycan is a crucial component of bacteria, and it influences several different facets of their biology. Scientists use differences in the peptidoglycan-based cell walls to classify different bacterial species.
Scientific American explains that the peptidoglycan cell wall serves a similar function as the skin of humans does. The cell wall limits the size and shape of the bacterial cell and helps to repel invading organisms. Bacterial cells are akin to salt bubbles in a lake of fresh water. If the cell walls do not keep the external environment separated from the internal environment, the cells tend to absorb fresh water in an attempt to reach osmotic equilibrium. If the cell walls develop damage and fresh water is allowed inside the cell, it's likely to burst. Scientists call this eventuality osmotic lysis.
Scientists use this principle to battle bacteria. Bacteria normally repair the damage to their cell walls, which prevents osmotic lysis; however, Scientific American states that penicillin, one of the world’s oldest and most useful antibiotics, works by preventing bacterial cells from repairing damage to the cell wall. As these damaged sections begin to accumulate, the seal around the bacteria fails, causing the death of the bacteria.