|MadSci Network: Cell Biology|
First off, the subject of free radicals has been covered extensively in past posts which can be accessed from our search engine at: http:// www.madsci.org/MS_search.html. Now, on to telomeres, telomerase, and aging:
Telomeres are stretches of repetitive DNA at the ends of chromosomes that allow faithful DNA replication by acting as primers for lagging-strand synthesis. As mentioned in the preceding link, each replication shortens the telomeres, until eventually they disappear and subsequent replications begin to chew away at the ends of the chromosomes. To counteract this loss, replicating cells contain an enzyme called telomerase which re-lengthens the telomeres between replications. The importance of telomerase came after years of frustration by researchers who found that several cell lines stopped growing in culture after a certain number of passages (divisions). They found that cells with activated telomerase could grow in culture indefinitely. This finding was hyped by the non-scientific media as a potential Fountain of Youth, and stories of telomerase allowing people to live forever and never age quickly sank into popular lore.
Meanwhile, researchers continued to examine this phenomenon, and found that the activity of telomerase and the length of the telomeres were intricately tied to programmed cell death (apoptosis), in so far as cells monitor their telomere lengths and commit suicide if they sense that they've replicated too many times. As it happens, this is very important in tissues like the skin and the lining of the gut, where new cells are constantly made as older cells slough off and die. If the older cells don't die but keep dividing instead, the result is more cells in the area than you want in a structure commonly called a tumor. If these cells find a way out of their tumor, they can become cancerous. In fact, "immortalization" was one of the first hallmarks described for cancerous cells, and is vital for tumor formation. The body normally prevents this by shutting off the telomerase gene in cells that are destined to be sloughed.
So, giving someone activated telomerase, or altering their endogenous telomerase genes to make them constitutively active would be a really bad idea. In fact, all of the cells in your body that are supposed to be proliferative express sufficient telomerase to last you throughout your lifetime. It is worth noting then that aging is not caused by your cells wearing out (since they don't), but is caused by the connective matrices (mostly collagen and elastin) around the cells wearing out.
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