Americans Elizabeth H. Blackburn, Carol W. Greider and Jack W. Szostak won the 2009 Nobel Prize in medicine Oct. 5 for discovering a key mechanism in the genetic operations of cells, an insight that has inspired new lines of research into cancer.

Elizabeth H. Blackburn (left) and Carol W. Greider, two of the three winners of the 2009 Nobel Prize in medicine, stand next to a bust of Paul Ehrlich in March before they were awarded a prize named after the German scientist. AP PHOTO

It was the first time two women have been among the winners of the medicine prize.

The trio solved the mystery of how chromosomes, the rodlike structures that carry DNA, protect themselves from degrading when cells divide.

The Nobel citation said the laureates found the solution in the ends of the chromosomes — features called telomeres that are often compared to the plastic tips at the end of shoelaces that keep those laces from unraveling.

Blackburn and Greider discovered the enzyme that builds telomeres — telomerase — and the mechanism by which it adds DNA to the tips of chromosomes to replace genetic material that has eroded away.

The prizewinners' work, done in the late 1970s and '80s, set the stage for research suggesting that cancer cells use telomerase to sustain their uncontrolled growth. Scientists are studying whether drugs that block the enzyme can fight the disease. In addition, scientists believe that the DNA erosion the enzyme repairs might play a role in some illnesses.

Ten women have won the prestigious medicine award since the first Nobel Prizes were handed out in 1901, but it was the first time that two women were honored in the same year.

The award includes a 10 million kronor ($1.4 million) purse split three ways among the winners.