Mitochondrially generated reactive oxygen species such as superoxide (O
—) and hydroxyl radicals (•OH) are free to attack methylene bridges adjacent to unsaturated carbon bonds in fatty acids. This results in the formation of lipid peroxidation products. Subsequent cyclization and beta-scission and can result in the formation of reactive alkenals such as 4-hydroxy-2-nonenal and malonaldehyde. These extremely reactive but more stable species can diffuse from their site of origin and result in protein and DNA damage. PUFA, polyunsaturated fatty acid. SOD Superoxide dismutase.