Szostak, Jack William, 1952–, American molecular biologist, b. London, England, Ph.D. Cornell, 1977. Szostak has been a professor at Harvard Medical School and a researcher at Massachusetts General Hospital since 1977. He shared the 2009 Nobel Prize in Physiology or Medicine with Carol Greider and Elizabeth Blackburn for solving the problem of how chromosomes make complete copies of themselves during cell division and how they protect themselves against degradation during this process. Szostak and Blackburn discovered that a unique DNA sequence in telomeres (the region of DNA at the ends of the chromosomes) protects the chromosomes from degradation. In addition to increasing understanding of the cell, the three researchers's work shed light on disease mechanisms and stimulated the development of potential new disease therapies.