In 1984, University of California, Berkeley biology professor Elizabeth Blackburn and then grad student Carol Greider made the discovery that a quarter century later would win them the Nobel Pnze: They identified telomerase as the enzyme that protects the DNA in our chromosomes, in effect keeping our cells-and, to some degree, us-young. But telomerase is naturally produced only minimally and intermittently in some of our cells-just enough to grt. disposable us a maximum life span of around 120 years. Unless, that is, someone figures out how to increase the telomerase inside our bodies. Such tinkering with the basic machinery of life has been a theoretical possibility since the 1990s, when scientists at the Bay Area biotech firm Geron and elsewhere identified the human telomerase gene.