Power, Sex, Suicide: Mitochondria and the Meaning of Life Read Online Free PDF

English-speaking world. For the first time, however, the case did not stand on the morphological similarities between mitochondria and bacteria, but turned on attempts to cultivate mitochondria as a cell culture. Portier claimed to have done so, at least with ‘proto-mitochondria’, which he argued had not yet become fully adapted to their life inside cells. His findings were publicly contested by a panel of bacteriologists at the Pasteur Institute, who were unable to replicate them. And sadly, once he had secured his chair at the Sorbonne, Portier abandoned the field, and his work was quietly forgotten.
    A few years later, in 1925, the American Ivan Wallin independently put forward his own ideas on the bacterial nature of mitochondria, claiming that such intimate symbioses were the driving force behind the origin of new species. His arguments again turned on culturing mitochondria, and he, too, believed that he had succeeded. But for a second time interest waned with the failure to replicate his work. This time symbiosis was not ruled out with quite the same venom, but the American cell biologist E. B. Wilson summed up the prevailing attitude in his famous remark: ‘To many, no doubt, such speculations may appear too fantastic for present mention in polite biological society; nevertheless it is within the range of possibility that they may some day call for some serious consideration.’
    That day turned out to be half a century later: aptly enough for the tale of an intimate symbiotic union, in the summer of love. In June 1967, Lynn Margulis submitted her famous paper to the
Journal of Theoretical Biology
, in which sheresurrected the ‘entertaining fantasies’ of previous generations and cloaked them in newly scientific apparel. By then the case was much stronger: the existence of DNA and RNA in mitochondria had been proved, and examples of ‘cytoplasmic heredity’ catalogued (in which inherited traits were shown to be independent of the nuclear genes). Margulis was then married to the cosmologist Carl Sagan, and she took a similarly cosmic view of the evolution of life, considering not just the biology, but also the geological evidence of atmospheric evolution, and fossils of bacteria and early eukaryotes. She brought to the task a consummate discernment of microbial anatomy and chemistry, and applied systematic criteria to determine the likelihood of symbiosis. Even so, her work was rejected. Her seminal paper was turned down by 15 different journals before James Danielli, the far-seeing editor of the
Journal of Theoretical Biology
, finally accepted it. Once published, there were an unprecedented 800 reprint requests for the paper within a year. Her book,
The Origin of Eukaryotic Cells
, was rejected by Academic Press, despite having been written to contract, and was eventually published by Yale University Press in 1970. It was to become one of the most influential biological texts of the century. Margulis marshalled the evidence so convincingly that biologists now accept her once-heterodox view as fact, at least when applied to mitochondria and chloroplasts.
    Bitter arguments persisted for well over a decade, and were arcane but vital. Without them, the final agreement would have been less secure. Everyone accepted that there are indeed parallels between mitochondria and bacteria, but not everyone agreed about what these really meant. Certainly the mitochondrial genes are bacterial in nature: they sit on a single circular chromosome (unlike the linear chromosomes of the nucleus) and are ‘naked’—they’re not wrapped up in histone proteins. Likewise, the transcription and translation of DNA into proteins is similar in bacteria and mitochondria. The physical assembly of proteins is also managed along similar lines, and differs in many details from standard eukaryotic practice. Mitochondria even have their own ribosomes, the protein-building factories, which are bacterial in appearance. Various antibiotics