The Fenton reaction leads to free radical generation when -

Ans. is 'c' i.e., Ferrous ions are conveed to ferric ions o Free radicals are generated through Fenton's reaction. o In this reaction iron is conveed from its ferrous to ferric form and a free radical is generated. i.e. (H202+Fe2+ --> Fe3++ OH++ OH-) o Note :- H202 can also react with copper instead of iron to produce free radicals. Free radicals o Free radicals are chemical species that have a single unpaired electron in the outer orbit. o Most of these are paially reduced reactive oxygen forms that are produced as an unavoidable byproduct of mitochondrial respiration --> also known as reactive oxygen species. o The most impoant are hydrogen peroxide (11202), Superoxide anion (02) and hydroxyl radical (OH). o Free radicals are highly reactive species and toxic --> they can damage the cell membrane and nucleic acids. o Free radicals initiate autocatalytic reactions, whereby molecules with which they react are themselves conveed into free radicals to propagate the chain of damage. o Free radicals are produced in several ways : ? I. Ionizing radiations (UV rays, X-rays) can hydrolyze water into hydroxyl (OH) and hydrogen (H) free radicals. Enzymatic metabolism of exogenous chemicals, e.g., CC14 can generate CC13. The reduction - oxidation reaction during normal metabolic process. During normal respiration, molecular oxygen is sequentially reduced by addition of electron to generate water. In this process small amount of H202, 02- and OH- are produced. o H202 generated, can interact with 02 to generate OH through the Haber-weiss reaction. H202+ 02 --> OH- + OH + 02 Rapid burst of superoxide (02) occur in activated neutrophils during inflammation with the help ofNADPH oxidase. Some intracellular oxidases, e.g., xanthine oxidase generate superoxide radicals. Transition metal such as iron and copper donate or accept free electrons and catalyze free radical formation (see above fenton reaction). Nitric oxide (NO) generated in endothelium, macrophages and neurons can also act as free radical. o Free radicals cause cell injury by ? I. Lipid peroxidation and subsequent damage of cellular and mitochondrial membrane. Oxidative modification and subsequent degradation of intracellular proteins. DNA strand break.