This is because the ends of chromosomes, structures called telomeres, shorten each time the cell divides.
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This is the role of structures called telomeres that cap the ends of chromosomes.
Telomeres protect the chromosomes, much like the plastic tips on shoelaces keep lace from fraying.
So the longer your telomeres are, the longer you can expect to live.
It centers on structures at the end of chromosomes called telomeres and an enzyme that forms them, called telomerase.
This is where the zebra finches came in: how early and accurately could longer telomeres predict a longer life?
But what remains unknown is why some people have longer telomeres than others.
Work by the researchers determined that telomeres protect DNA from degradation in the process, and that telomerase maintains the telomeres.
They are certain to raise the question of whether our telomeres are similar predictors of how long we will live.
The next step will be to find out why the length of telomeres can vary so much from individual to individual.
It markets a supplement called TA-65, which the company says lengthens telomeres, the caps on the ends of DNA associated with aging.
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Blackburn had been looking for an enzyme that helped telomeres stay intact.
They say the lengths of tiny pieces of DNA called telomeres indicate whether a young creature is likely to live long into old age.
In every case the longest lived birds had the longest telomeres, but the best predictor of lifespan was the length of the telomeres at just 25 days old.
Recent research found that meditation can result in molecular changes affecting the length of telomeres, a protective covering at the end of chromosomes that gets shorter as people age.
But it is a big leap from the laboratory to the real world - whatever our telomeres may say, human lifespans also have to contend with additional factors like diet, drink and stress.
We will be able to rejuvenate our organs in place by gradually replacing aging cells that contain genetic errors and short telomeres with cells containing our own DNA but without errors and with extended telomeres.
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But before you rush out to get your telomeres stretched - were such a process possible - it is worth pointing out that the creatures they have been working with are not humans but altogether shorter-lived zebra finches.
Greider, 48, along with her mentor Dr. Elizabeth Blackburn from the University of California, San Francisco, and Harvard scientist Dr. Jack Szostak, were given the Nobel Prize for their work with telomeres, which are the bits of repeating DNA at the end of our chromosomes.
The reason for this is believed to be to stop cancer in its tracks by preventing tumour cells from dividing more than a certain number of times. (Successful cancers often have a special enzyme that repairs telomeres.) The cost is that, eventually, even healthy tissue cannot renew itself.
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