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Telomere, by which is a terminal structure of
eukaryotic chromosomes was discovered at first in 1938 and has a vital role in
chromosome protection. Telomere in human and other vertebrates consists of
thousands of 5′-TTAGGG-3′
tandem repeats at the end of the chromosome, has a main role in the chromosome
stability. Telomere protects the end of the chromosome from degeneration,
rearrangement and end to end fusion. There is a telomere loss at every cell
division. Progressive loss in telomere length results in disassociation of
telomere binding proteins and change in gene expression profiles. Adjacent genes
are suppressed by the telomere effect so the telomere loss results in adjacent
gene expressions. Apoptosis and replicative senescence are caused by
progressive telomere loss. There are three mechanisms for increasing telomere
length in eukaryotes and telomerase is the predominant mechanism. Telomerase
can synthesize telomere, without the template. Telomerase is overexpressed In 90% of cancers. Therefore cancerous cells compensate
the telomere loss in every cell division because of telomerase. In conclusion,
telomerase is a proper target for cancer therapy and many methods including
direct inhibition of telomerase and immunotherapy have been introduced.
