Practice question

Aerobic respiration inherently leaks electrons to oxygen at Complex I and Complex II producing superoxide anion which dismutates to hydrogen peroxide and can generate highly destructive hydroxyl radical via Haber-Weiss and Fenton chemistry catalyzed by iron. These reactive oxygen species damage virtually all macromolecules including proteins forming carbonyls, lipids forming peroxides and DNA forming 8-oxoguanine leading to mutations. Bacteria deploy multilayered detoxification network. Superoxide dismutase encoded by sodA manganese cofactored, sodB iron cofactored and sodC copper-zinc periplasmic catalyzes rapid dismutation of superoxide to peroxide and oxygen lowering steady state to picomolar protecting dehydratases. Catalase isozymes KatG bifunctional and KatE monofunctional then convert peroxide to water and oxygen, while alkyl hydroperoxide reductase AhpCF scavenges low-level organic peroxides. Coordinated transcriptional induction via OxyR sensing peroxide and SoxR sensing superoxide ensures prompt response proportional to stress. Peptidoglycan hydrolase remodels wall, DNA helicase unwinds duplex, transpeptidase cross-links wall unrelated to ROS, distinguishing catalase and superoxide dismutase as canonical evolutionarily conserved ROS detoxifiers essential for aerobic growth and pathogenesis inside phagocytes.