Just why mitochondria assume this seemingly disparate role is the subject of speculation. Neil Blackstone, associate professor of biological sciences, Northern Illinois University, DeKalb, and Douglas Green, head of the division of immunology at the La Jolla Institute for Allergy and Immunology, Ontario, Calif., believe that it is an evolutionary issue, one that goes back to the mitochondria's roots as an endosymbiont.5 They suggest that after ancient eukaryotes took in protomitochondria, mitochondria were forced to interact with their environment through their hosts. The protomitochondria weren't completely at the eukaryotes' mercy, however; they could manipulate the host cell phenotype with by-products of ox-phos, and, in particular, reactive oxygen species (ROSs).
ROSs raise the mutation rate and, some think, sexual recombination along with it.6 In good times, that is, times of rapid growth, the mitochondria would crank out adenosine triphosphate (ATP), keeping the redox state of the mitochondria fully oxidized. However, during ...
