Figure 14.12 Inheritance of a single nuclear gene senescent mutant of Neurospora. A senescent mutant (S) was crossed to a wild strain of opposite mating type.

giving rise to a superoxide anion. A superoxide anion is highly destructive and leads to the formation of hydrogen peroxide, H2O2, and hydroxyl radicals, OH-, collectively called reactive oxygen species (ROS). ROS oxidize and damage nucleic acids, lipid and protein molecules and the damage to cells and tissues results in aging and ultimately to death. Since alternative oxidase (Figure 14.14) is located upstream of complex III, the production of ATP is restricted to complex I and consequently the production of ATP is lowered. To determine which of the aforementioned biochemical modifications is the primary cause of senescence, Dufour et al. (2000) examined the effects of specific inactivation of cytochrome oxidase on life-span, ROS formation, senDNA accumulation—modifications implicated in senescence. Since P. anserina has (i) a short life-span, (ii) a cytochrome-mediated aerobic respiratory pathway, (iii) an alternative respiratory pathway linking the oxidation of ubiquinol directly to the reduction of oxygen to water and playing a crucial

'A "A Ubiquinone 111

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