Abstract
Living species are continuously subjected to all extrinsic forms of reactive oxidants and others that are produced endogenously. There is extensive literature on the generation and effects of reactive oxygen species (ROS) in biological processes, both in terms of alteration and their role in cellular signaling and regulatory pathways. Cells produce ROS as a controlled physiological process, but increasing ROS becomes pathological and leads to oxidative stress and disease. The induction of oxidative stress is an imbalance between the production of radical species and the antioxidant defense systems, which can cause damage to cellular biomolecules, including lipids, proteins and DNA. Cellular and biochemical experiments have been complemented in various ways to explain the biological chemistry of ROS oxidants. However, it is often unclear how this translates into chemical reactions involving redox changes. This review addresses this question and includes a robust mechanistic explanation of the chemical reactions of ROS and oxidative stress.
Highlights
In chemistry, a free radical (FR) is a relatively stable species that contains one or more unpaired electrons and can react with other molecules, either by donating its unpaired electron to another molecule or by taking it away from another molecule to increase stability.In this way it converts the molecule with which it reacts into another FR, so a common feature of FR reactions is the chain process: one radical gives rise to another radical
Addition of water on the carbon and formation of the hydroxy toreactions form the by enamine derivative which evolves to the unsaturated imine by lossThe of the phosphate tion free radicals, with the formation of carbon-centred radicals
Hydroxyl radicals can be added to the C-8 position of guanine and generate a radical on the nitrogen at position 7 (Figure 10), which can be reduced by the addition of an electron and a proton to an unstable intermediate, giving the ring-opening fragmentation product
Summary
A free radical (FR) is a relatively stable species that contains one or more unpaired electrons and can react with other molecules, either by donating its unpaired electron to another molecule or by taking it away from another molecule to increase stability In this way it converts the molecule with which it reacts into another FR, so a common feature of FR reactions is the chain process: one radical gives rise to another radical. Oxidants are released during the folding of proteins and the formation of disulphide bonds They are highly reactive chemical molecules derived from the ability of the O2 molecule to accept electrons [3], generating subsequent unstable molecules such as superoxide anion ( O2 − ), hydrogen peroxide (H2 O2 ), hydroxyl radical (OH− ), and singlet oxygen (1 O2 − ), produced by all kinds of cells. On the other hand, when they are produced in excess or when cellular defences are not able to metabolise them, oxidative stress (OS) damage occurs [5]
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