Australian-American researcher Elizabeth Blackburn and Carol Greider and Jack Szostak of the United States won the Nobel Medicine Prize on Monday for identifying a key switch in cellular ageing.
The trio were honoured for the discovery of how chromosomes are protected by telomeres and the role of an enzyme called telomerase in maintaining or stripping away this molecular shield.
"The award of the Nobel Prize recognises the discovery of a fundamental mechanism in the cell, a discovery that has stimulated the development of new therapeutic strategies," the Nobel jury said.
Blackburn and Greider are only the ninth and tenth women to win the Nobel Medicine Prize since 1901 -- out of a total 195 medicine laureates -- and this is the first time two women have shared the honour.
But Nobel committee secretary Goeran Hansson said gender played no part in the decision.
"They're not being honoured because they are women. They are being honoured because they've made a fundamentally important discovery," he told Swedish news agency TT.
The three laureates told Swedish Radio they were overjoyed by the news.
Greider, born in 1961 and a molecular biology and genetics professor at Johns Hopkins University School of Medicine in Baltimore, was "just thrilled."
"I just think that the recognition for curiosity-driven basic science is very, very nice," she said, adding that she was up doing laundry in the US when the early morning call came from Sweden.
Blackburn, born in 1948, who teaches biology and physiology at the University of California in San Francisco, said she knew when they made their Christmas Day 1984 discovery that they were on to something big.
"I felt very excited ... and I thought this is very interesting, this is a very important result, and you don't often feel that about a result," she said.
Szostak, 56, a professor of genetics at Massachusetts General Hospital in Boston, said he planned to celebrate with "a big party at some point."
Telomeres are a minute yet vital factor in ageing. They are like a nubby, protective cap, fitting on the ends of the strands of DNA -- the chemical recipe for life -- that are packed into chromosomes.
Blackburn and Szostak discovered in 1982 that a unique DNA sequence in the telomeres protects the chromosomes from degradation when the cells divide. With Greider, Blackburn also identified telomerase, the enzyme that makes the telomere DNA.
If telomeres become worn, cells age.
But if telomerase levels are high, the telomere length is maintained, and cellular ageing is braked. A small number of rare but very destructive diseases, including a form of severe anaemia, are linked to defective telomerase, resulting in damaged cells.
Yet there is also a darker and more complex side to this picture.
Many experts initially speculated that ageing could be pinned to telomere shortening, but the process has emerged as something that encompasses different factors, as well as telomeres.
In addition, high telomerase also helps cancer, enabling its cells to replicate endlessly and achieve what scientists call "cellular immortality."
Finding ways of blocking this machinery through "telomerase inhibitors" is one of the most eagerly explored areas of cancer research.
The trio's work has "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.
The three won the 2006 Lasker Prize, one of the most prestigious US science awards, for the same work.
The Medicine Prize is the first award to be announced in this year's Nobel season.
The Physics Prize is to be announced on Tuesday followed by the Chemistry Prize on Wednesday. The Literature Prize will be announced on Thursday and the Peace Prize on Friday.
The Economics Prize will wrap up the awards on October 12.
The laureates receive a gold medal, a diploma and 10 million Swedish kronor (1.42 million dollars, 980,000 euros) which can be split between up to three winners per prize. The prizes are awarded in Stockholm and Oslo on December 10.