Telomere

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A telomere is a region of repetitive DNA at the end of a chromosome, which protects the end of the chromosome from deterioration. Its name is derived from the Greek nouns telos (τέλος) "end" and merοs (μέρος, root: μερ-) "part". The telomere regions deter the degradation of genes near the ends of chromosomes by allowing for the shortening of chromosome ends, which necessarily occurs during chromosome replication.[1]

Russian theorist Alexei Olovnikov was the first to recognize (1971) the problem of how chromosomes could replicate right to the tip, as such was impossible with replication in a 5' to 3' direction. To solve this and to accommodate Leonard Hayflick's idea of limited somatic cell division, Olovnikov suggested that DNA sequences would be lost in every replicative phase until they reached a critical level, at which point cell division would stop.[2][3]

During cell division, enzymes that duplicate DNA cannot continue their duplication all the way to the end of the chromosome. If cells divided without telomeres, they would lose the ends of their chromosomes, and the necessary information they contain. The telomeres are disposable buffers blocking the ends of the chromosomes and are consumed during cell division and replenished by an enzyme, the telomerase reverse transcriptase.

In 1975–1977, Elizabeth Blackburn, working as a postdoctoral fellow at Yale University with Joseph Gall, discovered the unusual nature of telomeres, with their simple repeated DNA sequences composing chromosome ends. Their work was published in 1978. The telomere shortening mechanism normally limits cells to a fixed number of divisions, and animal studies suggest that this is responsible for aging on the cellular level and sets a limit on lifespans. Telomeres protect a cell's chromosomes from fusing with each other or rearranging — abnormalities that can lead to cancer — and so cells are destroyed when their telomeres are consumed. Most cancers are the result of "immortal" cells that have ways of evading this programmed destruction.[4]

Elizabeth Blackburn, Carol Greider, and Jack Szostak were awarded the 2009 Nobel Prize in Physiology or Medicine for the discovery of how chromosomes are protected by telomeres and the enzyme telomerase.[5]

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