Oxidative phosphorylation

cells take high-energy electrons and release their energy in a controlled manner
the body passes electrons to oxygen
but oxygen is impatient and wants the high-energy electrons
ca. 1-2% of the high-energy electrons are grabbed by oxygen
oxygen turns into hulk: superoxid type of free radical
superoxid is out of control, smashes around the cell, is damaging the DNA: Mitochondrial theory of aging
this process is also called oxidative stress