Today, three U.S. researchers were awarded the 2009 Nobel Prize in Physiology or Medicine. Australian-American researcher Elizabeth Blackburn, Carol Greider and Jack Szostak, won the prize for their 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 recognizes the discovery of a fundamental mechanism in the cell, a discovery that has stimulated the development of new therapeutic strategies," the Nobel jury said.

Telomeres are a minute yet vital factor in aging. 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 aging 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.

For the official announcement visit: http://nobelprize.org/nobel_prizes/medicine/laureates/2009/