Telomeres are repetitive sequences of base pairs of our DNA at the end of each of our chromosomes, in humans the telomere sequence is TTAGGG, and this is the same for most animals.
Our telomeres are important because when our DNA is copied (this happens every time a cell divides) the polymerases which copy DNA do not start from the very tip, so if we did not have telomeres, we would loose a little bit of genetic material every time we needed to make a new cell, leaving raggedy gene ends which could lead to mutations (which could cause cells to form tumors). Telomeres also stop the ends of different chromosomes sticking together and altering our genetic makeup. In a way telomeres act like an aglet to our chromosome shoelaces, by protecting the ends from wear and tear.
When we are born, our telomeres are up to 15000 base pairs long (though each individual has a genetically determined number). Each time our cells divide by mitosis, we lose around 30-200 base pairs from our telomeres. This gives most of the cells in our body a lifespan of 50-70 divisions, after which they usually 'die' in a way that does not affect the working of neighbouring cells known as cell senescence. However sometimes can continue to divide causing mutations as less genetic material is copied in successive cell divisions. Notably, artery wall cells have far shorter telomeres than those in veins due to stress, damadge and therefore the need for the replication of cells.
Our bodies also produce an enzyme called telomerase reverse transcriptase which adds base pairs to the end of our telomeres, preventing them from shortening too quickly, however this process appears to stop in adult cells. This enzyme is also responsible for the 'immortality' of cancerous cells which divide rapidly. There is hope amongst scientists to prevent the development of tumours by inhibiting telomerase, however this can have significant side effects such as problems with fertility, wound healing and blood cell production.
Studies on mice in November 2012 have shown that their rate of telomere shortening is 100 faster than in humans and perhaps accountable for the difference in lifespan between our species. The studies also have shown that exending telomeres can increase life expectancy in mice by up to 24% and postpone the advance of age related diseases such as osteoporosis and insulin-resistance. 20 year studies on birds (without natural predators) in the Seychelles, found links between longer telomeres and longer life as well as rapidly shortening telomeres as a sign of a bird within the last year of its life.
Links between telomere length and shortening have been linked to aging and many human diseases, people with shorter telomeres are apparently 3 times more likely to suffer from cardiovascular diseases; 8 times more likely to suffer form infectious diseases; there have beeen links to Alzheimers disease as well as bone, prostate, bladder and kidney cancers to name a few. Telomere length also has direct links to Werner's syndrome (where oxidative stress cannot be repaired) and Dyskeratosis congenita (where telomeres shorten rapidly), diseases both with symptoms of premature aging.
Links have been found between the age of a child's father and telomere length as unlike body cells, the sex cells increase telomere length with age, so the father will pass on these longer telomeres to his offspring.
Some laboratories are offering blood tests to determine telomere length, the '£400 blood test to tell you when you will die'. However this advertisment was misleading and was exaggerated by the media, as longevity cannot be predicted through one blood test, due to the huge varaition between people's original telomere length. Though discovering a fast rate of telomere shortening could be an incentive to improve liefstyle (for example telomeres are shortened by oxidative stress, a process which is prevented by eating antioxidants)
An issue however is that if further studies were to confirm that telomeres played a significant role in causing aging and age-related diseases, that insurance companies or employers could use the imformation about an individual's telomere length to discriminate against that individual.
There is hope that by studying the action of telomerase in cancer cells and its apparent ability to provide cell immortality that we could potentially postpone the aging process. Natural selection only prepared us to outlive our offsping, but now with an aging population due to the irradication of many diseases which have blighted our species in the past, are telomeres the final barrier to immortality?
Definitions:
Base pairs, our DNA is made of pairs of complementary molecules, one on each strand, bonded together
Enzymes, proteins in the body which speed up metabolic reactions
Mitosis, cell division where by cells make an identical copy of their genetic material
Polymerases, a type of enzyme that copies DNA
Oxidative stress, is an imbalance between the production of reactive oxygen and the body's abillity to restore the balance of oxidants
Sources:
Genome by Matt Ridley
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