الفهرس 
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Abstract
Mitochondria are membrane-bound cytoplasmic organelles, variable in size, shape and number from one type of cell to another. They are considered the power house of the cell as they are responsible for the production of energy through oxidation of various food substances. O2 is both essential to human life and toxic. We are dependent on O2 for oxidation reactions in the pathways of adenosine triphosphate (ATP) generation, detoxification, and biosynthesis. However, when O2 accepts single electrons, it is transformed into highly reactive oxygen radicals that damage cellular lipids, proteins, and DNA. Damage by reactive oxygen radicals contributes to cellular death and generation in a wide range of diseases. Radicals are compounds that contain a single electron, usually in an outside orbital. Oxygen is a biradical, a molecule that has two unpaired electrons in separate orbitals. Through a number of enzymatic and non-enzymatic processes that routinely occur in cells, O2 accepts single electrons to form reactive oxygen species (ROS). ROS are highly reactive oxygen radicals, or compounds that are readily converted in cells to these reactive radicals. The ROS formed by reduction of O2 are the radical superoxide (O2-), the non-radical hydrogen peroxide (H2O2), and the hydroxyl radical (OH•). Various methods have been used to minimize the disastrous effect of ROS on the body including antioxidants intake either from naturally occurring sources as green tea, broccoli, and nuts, or as diet supplements, also caloric restriction in daily meals. Vitamin E is considered the most widely used fat-soluble antioxidant, preventing peroxidation of membrane phospholipids, thus preserving cell integrity and proper function.