Prof. Rune Toftgard, right, talks about the 2009 Nobel Prize winners for medicine at the Nobel Forum of the Karolinska Institute in Stockholm on Monday. (Bertil Ericson/Associated Press)

Three U.S. scientists, Elizabeth Blackburn, Carol Greider and Jack Szostak, have received the 2009 Nobel Prize in Medicine for their chromosome research.

The Karolinska Institute in Sweden said Monday the trio was honoured for the discovery of how chromosomes are protected by telomeres and the enzyme telomerase, which has implications for cancer and aging research.

"We had no idea when we started this work that telomerase would be involved in cancer, but were simply curious about how chromosomes stayed intact," Greider, 48, said in a statement.

The discovery by the trio determined how chromosomes can be "copied in a complete way during cell divisions and how they are protected against degradation," according to the citation.

The laureates found the solution in the ends of the chromosomes — the telomeres — and in an enzyme that forms them.

The telomeres, which serve as small caps at the ends of chromosomes, prevent cells from degrading. Some inherited diseases are now known to be caused by telomerase defects, including certain forms of congenital aplastic anemia as well as inherited diseases of the skin and the lungs.

The trio found the enzyme that builds telomeres and the mechanism by which it adds DNA to the tips of chromosomes to replace genetic material that has eroded away.

'Major problem in biology'

The discoveries have "solved a major problem in biology" and have added "a new dimension to our understanding of the cell, shed light on disease mechanisms, and stimulated the development of potential new therapies," the Nobel citation said.

U.S. biologists Elizabeth H. Blackburn from San Francisco, left, and Carol Greider from Baltimore pose next to a bust of Paul Ehrlich before they were awarded the Paul Ehrlich and Ludwig Darmstaedter science prize in Frankfurt, Germany, in March. (Michael Probst/Associated Press)

"When we started the work, of course, we were really just interested in the very basic question about DNA replication, how the ends of chromosomes are maintained," Szostak, 56, told The Associated Press. "At the time we had no idea there would be all these later implications."

Scientists are now 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.

"This has broad medical implications for cancer, certain inherited diseases and for aging," said Rune Toftgard, who announced the award.

Prize committee member Goran Hansson said there is a lot of work yet to do to develop therapies for blood, skin and lung disease based on the winners' breakthroughs.

The award, announced Monday, includes a 10 million kronor ($1.5 million) purse, a diploma and an invitation to the prize ceremonies in Stockholm on Dec. 10.

38 women have received Nobel

It is the first-time two women have been named winners of the medicine prize in the same year. Only 36 other women have received Nobel Prizes since they were first handed out in 1901.

Jack Szostak speaks on the phone at his home in Boston on Monday after learning that he is one of three Americans to win the Nobel Prize in Medicine. (Brian Snyder/Reuters)

Blackburn, 60, holds U.S. and Australian citizenship and is a professor of biology and physiology at the University of California, San Francisco.

Greider is a professor in the department of molecular biology and genetics at Johns Hopkins University School of Medicine in Baltimore.

Szostak, a U.S. citizen who was born in London, England, grew up in Canada and studied at McGill University in Montreal. He has been at Harvard Medical School since 1979 and is currently professor of genetics at Massachusetts General Hospital in Boston.

Canadian scientists Ernest McCulloch and James Till, whose 1960s discovery of stem cells paved the way for controversial research, were considered contenders for the prize.

Analysts have said the U.S. trio could also be up for the Nobel Prize in Chemistry.

The prize announcement is the first of six prizes focusing on medicine, physics, chemistry, economics, literature and the Peace Prize that will be announced through Oct. 12.

Alfred Nobel, the Swede who invented dynamite, established the prizes in his will in the categories of medicine, physics, chemistry, literature and peace. The economics prize is technically not a Nobel but a 1968 creation of Sweden's central bank.

Nobel left few instructions on how to select winners, but medicine winners are typically awarded for a specific breakthrough rather than a body of research.

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With files from The Associated Press