Biochemistry of Free Radicals and Antioxidant: A Systematic Review

Free radicals are highly reactive molecular species characterized by the presence of one or more unpaired electrons, which makes them capable of initiating oxidative reactions in biological systems. In living organisms, free radicals particularly reactive oxygen species (ROS) and reactive nitrogen species (RNS) are generated continuously as by-products of normal metabolic processes such as mitochondrial respiration, inflammatory responses, and enzymatic reactions. At physiological levels, free radicals play beneficial roles in cellular signaling, immune defense, and regulation of gene expression. However, excessive generation of free radicals or impairment of antioxidant defense mechanisms results in oxidative stress, a condition implicated in the development of numerous pathological conditions including cancer, cardiovascular diseases, diabetes mellitus, neurodegenerative disorders, and aging. Antioxidants are molecules that counteract the harmful effects of free radicals by neutralizing them, thereby preventing oxidative damage to vital biomolecules such as lipids, proteins, and nucleic acids. The antioxidant defense system consists of both enzymatic antioxidants such as superoxide dismutase, catalase, and glutathione peroxidase and non-enzymatic antioxidants including vitamins C and E, glutathione, carotenoids, and polyphenols. This seminar reviews the biochemical nature of free radicals, their sources and mechanisms of generation, and the molecular basis of oxidative damage. It also examines the classification, mechanisms, and biological significance of antioxidants, emphasizing their role in maintaining redox homeostasis and preventing oxidative stress-related disease