Unravelling the secrets of ageingBMJ 2009; 338 doi: https://doi.org/10.1136/bmj.a3024 (Published 08 January 2009) Cite this as: BMJ 2009;338:a3024
- Susan Mayor, freelance journalist
Evidence is growing that every chromosome in the body carries a marker that counts down from the day of birth to death, rather like a cellular sand clock. These biological timers are telomeres—repeat sequences of DNA that, together with associated proteins, cap the ends of chromosomes and protect them from degradation, just as the plastic coating on the ends of shoelaces stops them from fraying.
Research has shown that telomeres shorten with each cell division, gradually marking off the time to cell death.1 This shortening is accelerated in diseases associated with ageing—particularly cardiovascular disease and cancers—and in the presence of risk factors for these diseases such as obesity and high blood pressure. The hope for the future is that measurements of telomere length could be used to detect early disease, allowing preventive measures to be put in place, and eventually that methods will be found to slow or even reverse the shortening.
DNA polymerase—The enzyme that replicates DNA
3′ end of linear DNA—The two ends of a single strand of DNA are called 3′ (prime) and 5′. DNA is synthesised from the 5′ to 3′ direction
Oxidative stress—The level of oxidative damage in a cell caused by reactive oxygen species such as free radicals
Telomeres and ageing
Telomeres are made up of a large number of tandem repeats of the sequence TTAGGG. The enzyme DNA polymerase cannot fully replicate the 3′ end of linear DNA, so telomeres shorten progressively with each repeated cell division. Laboratory studies have shown that the telomere length of replicating cells is inversely correlated with age.
More than 30 years ago, Olovnikov proposed that this shortening could provide a mechanism for a biological clock that determines cell behaviour.2 This theory—sometimes …