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Oxidative stress

Whilst molecular oxygen (O2) is necessary for the release of energy during respiration, derivative forms of O2, termed reactive oxygen species (ROS) are produced endogenously by cells under aerobic conditions. These ROS include the superoxide radical (O2--), hydrogen peroxide (H2O2), and the hydroxyl radical (-OH), which can damage cell components, contribute to cellular ageing, and ultimately lead to cell death (Beckman and Ames, 1998). Specific effects include lipid peroxidation (Girotti, 1998), protein inactivation (Cabiscol et al., 2000), and nucleic acid damage (Salmon et al., 2004; Ribeiro et al., 2006), including damage to mitochondrial DNA, which can lead to the generation of respiratory-deficient ‘petite' mutants (O'Rourke et al., 2002; Doudican et al., 2005; Gibson et al., 2006). Oxygen's apparently contradictory roles within the cell, that is being essential for aerobic respiration and other metabolic processes, whilst being inherently toxic, have been referred to as the ‘oxygen paradox' (Davies, 1995).

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