telomeres

A telomere is a region of highly repetitive DNA at the end of a linear chromosome that functions as a disposable buffer. Every time linear chromosomes are replicated during late S phase, the DNA polymerase complex is incapable of replicating all the way to the end of the chromosome; if it were not for telomeres, this would quickly result in the loss of vital genetic information, which is needed to sustain a cell's activities. Every time a cell with linear chromosomes divides, it will lose a small piece of one of its strands of DNA. This process has been referred to by James Watson and Alexei Olovnikov as the "end replication problem" (1971). It is believed that telomeres have a function in the ageing process.
See more at Wikipedia.org...

Noun
1. either (free) end of a eukaryotic chromosome; "telomeres act as caps to keep the sticky ends of chromosomes from randomly clumping together"
(hypernym) end
(part-holonym) chromosome

A series of repeated DNA sequences at the 5´ end of a chromosome that ensure correct chromosome replication during cell division; each time a cell divides, some of the telomeres are lost in the process, eventually leaving little or no telomeres and resulting in cell death.