Earth's life depends mainly on the availability of oxygen in the terrestrial
biosphere. Based on geochemical records of existing terrestrial oxides, oxygenic
photosynthesis occurred in the cyanobacterial precursors approximately 2800 Ma ago.
The oxygen level in the atmosphere is now 21%. The human cells use this oxygen to
extract the necessary energy through mitochondrial respiration using the reactions of
the redox system that involves the transfer of electrons, enzymatic agents, and reactive
oxygen species, mainly superoxide radical (O.-
2), hydroxyl radical (.OH) and hydrogen
peroxide (H2O2). The different reaction mechanisms from and to produce reactive
oxygen species with their reaction constants in aquatic environments are presented
here, as well as their production through the Fenton reaction. Oxidative stress is an
imbalance between both normal oxygen-free radicals’ production and the cell's ability
to detoxify it.
Keywords: Enzymatic Reactivity, Great oxidation event-GOE, Hydrogen
peroxide (H2O2), Hydroxyl radical (.OH), Lipid peroxidation, Oxygenic
photosynthesis, Reactive oxygen species in aquatic environments, (ROS), ROS
cytotoxicity, Superoxide anion (O.-
2).
