A telomere [tel-uh-meer] is a protective region of repetitive DNA at the end of a chromosome, 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. 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.
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 also 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.
The Daily Omnivore 
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