Telomeres/telomeres/telomere/Telomere
Telomeres are repeats of the short-base sequence, TTAGGG, and its complement in all mammalian species, at the ends of each chromosome. In human cells, telomeres are approximately 8,000–10,000 bp in length with a single-stranded TTAGGG overhang of 100–400 bases on the 3’ end.
Telomeres do not encode genes, but rather prevent chromosome ends from being recognized as double-strand breaks .
Moreover, because of the end-replication problem, bases at the very tip of each chromosome are lost with each round of cell division. This progressive telomere shortening, to a critically short length, has been shown to be responsible for the Hayflick limit, the finite number of cell divisions that may occur before a cell enters the permanently non-dividing state termed replicative se nescence.
Hence, telomeres serve as a biological clock.
Finally, work from several laboratories has shown that telomeres play an important role in triggering DNA damage responses, although the physiological role of this telomere-based signaling is as yet poorly understood.
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