reactive oxygen species (ROS)

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reactive oxygen species (ROS)

any oxygen-containing compound that is particularly reactive. From both exogenous and endogenous sources, ROS are present in all aerobic organisms, which have evolved defences against their potentially damaging effects and also ways of utilizing them (e.g. for signalling between and within cells and in the immune system, for killing invading micro-organisms). Some but not all ROS are free radicals (e.g. the superoxide anion (·O2-) and the hydroxyl radical (OH·) where an atom has one or more unpaired electrons in its outer orbital, making it particularly reactive. All the better known free radicals in the body are oxygen-based (although other atoms can also exist in this form) and are generated as by-products of oxidative metabolism. They are formed by exposure to ionizing radiation, cigarette smoke and other environmental pollutants and increased by excessive alcohol consumption and in infections. Free radicals are believed to cause cellular damage by lipid peroxidation which incorporates oxygen into membrane lipids. Protein and DNA damage are also involved. They are implicated in ageing and disease, including atherosclerosis (hence coronary heart disease and stroke), cancers and obstructive lung disease. Antioxidant enzymes protect cell membranes by reacting with the free radicals and removing them (e.g. removal of ·O2- by superoxide dismutase which produces hydrogen peroxide (H2O2), itself an ROS). In sport, ROS may be responsible for delayed-onset muscle soreness (DOMS). See also antioxidant enzymes, antioxidant nutrients, oxidative stress, lipids, vitamins.
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