Three American scientists win The Nobel Prize in Physiology or Medicine 2009 "for the discovery of how chromosomes are protected by telomeres and the enzyme telomerase."  The announcement, credits Elizabeth Blackburn, from the University of California San Francisco (USA), Carol Greider, from Johns Hopkins University (USA), and Jack Szostak, from  Harvard Medical School (USA) with "the discovery of a fundamental mechanism in the cell, a discovery that has stimulated the development of new therapeutic strategies." Drs. Blackburn and Szostak discovered that the solution to chromosome replication was contained in telomeres, the endcaps on chromosomes that exert a protect effect during cell divisions.  As a graduate student, Dr. Greider assisted in the identification of telomerase, the enzyme that responsible for telomere DNA.