New Scientist Turning back the years - Features: "AGEING is as inevitable as death and taxes. And when your skin starts to sag, your hair turns grey and your muscles slowly lose their strength, you can't help dreaming of forcing the sands of time back up into the hourglass.
Yet before we can hope to stem the flow, let alone reverse it, we need to know just what this sand consists of. Pinning down the molecular changes that underlie the ageing process is not easy. But it has long been suspected that mitochondria, the energy-generating structures within almost every cell of the body, play a key role. And in the past couple of years, researchers have produced strong evidence that this is indeed the case, that the decline of mitochondria determines when our bodies begin to crumble.
And some don't stop there. The techniques they are developing to cure mitochondrial diseases, they say, might someday allow us to rejuvenate our mitochondria - and thus delay the onset of old age.
Essentially, what mitochondria do is burn sugars to produce energy. It's a slow and controlled form of burning, but it can still be dangerous. Any errors or interruptions result in the production of highly reactive free radicals that can damage DNA.
The vast majority of a cell's DNA is tucked away in the nucleus, far from the danger. But mitochondria have their own genome, a small circular bit of DNA containing just 13 protein-coding genes. Not only is this DNA at ground zero of the free-radical barrage, it also lacks the sophisticated machinery for repairing DNA damage found in the nucleus of cells - making it especially vulnerable to mutations.
What's more, a single cell can have hundreds of mitochondria, each containing as many as 10 copies of this genome, and this DNA is replaced much more often than nuclear DNA. Each time it replica"