An atom or group of atoms with an unpaired valence electron. Free radicals are formed when a bond is broken without forming ions. Because of their unpaired electrons, most free radicals are extremely reactive. For example, superoxide free radicals, formed in the body during normal metabolic processes and as a reaction to toxins and infections, have damaging effects on cells and tissues. See also antioxidants; reactive oxygen species; superoxide dismutase.
Subjects: Medicine and Health — Biological Sciences.