بسم الله الرحمن الرحيم Free Radicals الجذور الحرة فكرة من 100 عام It is now 100 years since Moses Gomberg discovered the first organic free radical ويقصد بهذا المصطلح ذرة فاقدة الكترون ( محتاجه الكترون) ، ولهذا فهي ذرة غير مستقرة وتتوق للاستقرار بالحصول على هذا الالكترون . كيف نفسر هذا الكلام هناك أربع طرق لحدوث الجذور الحرة 1/Initiation Some molecules contain relatively weak covalent bonds, which under the correct energetic conditions, can break to give two molecules or atoms, each containing an unpaired electron. This type of bond breaking is known as homolysis or homolytic bond cleavage. (visible-light, UV or X-rays) Propagation /2 Once the radical has been formed it can undergo abstraction (e.g. cyclisation ) or addition (e.g. polymers ) reactions, to form more stable radical or non-radical products. These propagation reactions generally work because they break weak bonds in the reactants and make strong bonds in the products. Termination /3 In competition with propagation reactions are termination reactions. Whereas propagation reactions have one radical reactant and one radical product, termination reactions lead to the destruction of radicals (i.e. no new radicals are produced from these reactions). An important termination reaction involves the combination (or coupling) of radicals to form dimers. Chain reactions /4 Most radical reactions involve a chain mechansim in which an initial radical undergoes a series of propagation reactions. These reactions ultimately lead to regeneration of the initial radical and the formation of a chain. Chlorination of methane تسميات اخرى In biochemistry, the free radicals of interest are often referred to as reactive oxygen species (ROS) because the most biologically significant free radicals are oxygen-centered المضار المصاحبة للجذور الحرة Free radical damage within cells has been linked to a range of disorders including cancerarthritisatherosclerosisAlzheimer's diseasediabetes This involvement is not at all surprising as free radical chemistry is an important aspect of phagocytosis, inflammation, and apoptosis. Cell suicide, or apoptosis, is the body's way of controlling cell death and involves free radicals and redox signalling. Redox factors play an even greater part in other forms of cell death such as necrosis or autoschizis الأسباب environmental pollutioncigarette smoke ultraviolet lightdrugschemicals... طرق الوقاية Antioxidants مضادات الاكسدة Antioxidants are molecules that scavenge for harmful oxygen-centred radicals (HO., RO They react with the harmful radicals before they get a chance to damage the bodyNaturally occurring antioxidants include vitamins C and E, which are found in many plants (including citrus fruits and vegetables), nuts and seeds. Indeed, vitamin E is often present in margarine and this prevents radical reactions leading to deterioration (or rancidity). Antioxidants have been proposed to play an important role in preventing cancer, heart disease, immune-deficiency diseases and ageing. However, the jury is still out as to which groups, if any, benefit from taking antioxidant supplements