Antioxidant

Antioxidants are compounds that inhibit oxidation, a chemical reaction that can take free radicals in addition to chain reactions that may harm the cells of organisms. Antioxidants such as thiols or ascorbic acid vitamin C may act to inhibit these reactions. To balance oxidative stress, plants as well as animals sustains complex systems of overlapping antioxidants, such(a) as glutathione.

The only dietary antioxidants are vitamins A, C, in addition to E. the term antioxidant is also used for industrial chemicals added during manufacturing to prevent oxidation in synthetic rubber, plastics, and fuels, or as preservatives in food and cosmetics.

While ] Additionally, supplementation with selenium or vitamin E does non reduce the risk of cardiovascular disease.

Oxidative challenge in biology

A paradox in metabolism is that, while the vast majority of complex life on Earth requires oxygen for its existence, oxygen is a highly reactive factor that damages alive organisms by producing reactive oxygen species. Consequently, organisms contain a complex network of antioxidant metabolites and enzymes that realize together to prevent oxidative waste to cellular components such as DNA, proteins and lipids. In general, antioxidant systems either prevent these reactive breed from being formed, or remove them before they can damage vital components of the cell. However, reactive oxygen rank also have useful cellular functions, such as redox signaling. Thus, the function of antioxidant systems is non to remove oxidants entirely, but instead to keep them at an optimum level.

The reactive oxygen species present in cells add hydrogen peroxide H₂O₂, hypochlorous acid HClO, and free radicals such as the hydroxyl radical ·OH and the superoxide anion O₂^{−. The hydroxyl radical is particularly unstable and will react rapidly and non-specifically with near biological molecules. This species is present from hydrogen peroxide in metal-catalyzed redox reactions such as the Fenton reaction. These oxidants can damage cells by starting chemical combine reactions such as lipid peroxidation, or by oxidizing DNA or proteins. Damage to DNA can cause mutations and possibly cancer, if not reversed by DNA repair mechanisms, while damage to proteins causes enzyme inhibition, denaturation and protein degradation.}

The ownership of oxygen as element of the process for generating metabolic energy produces reactive oxygen species. In this process, the superoxide anion is produced as a by-product of several steps in the electron transport chain. particularly important is the reduction of coenzyme Q in complex III, since a highly reactive free radical is formed as an intermediate Q·^{−. This unstable intermediate can lead to electron "leakage", when electrons jump directly to oxygen and form the superoxide anion, instead of moving through the normal series of well-controlled reactions of the electron transport chain. Peroxide is also produced from the oxidation of reduced flavoproteins, such as complex I. However, although these enzymes can produce oxidants, the relative importance of the electron transfer multinational to other processes that generate peroxide is unclear. In plants, algae, and cyanobacteria, reactive oxygen species are also produced during photosynthesis, particularly under conditions of high light intensity. This case is partly offset by the involvement of carotenoids in photoinhibition, and in algae and cyanobacteria, by large amount of iodide and selenium, which involves these antioxidants reacting with over-reduced forms of the photosynthetic reaction centres to prevent the production of reactive oxygen species.}