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Abstract
Telomers are specialized DNA protein structures located at the end of eukaryotic chromosomes. They play an essential role in the stable maintenance of the eukaryotic chromosomes within the cell by serving as specific binding sites for structural proteins. The proteins Cap the ends of linear chromosomes, thus preventing end to end fusion and other events that are normally lethal to the cell. A progressive shortening of the chromosome ends with each replication cycle results from DNA polymerase inability to replicate linear DNA to its very ends.
The maintenance of stable telomeres length in replicating cells is associated with the activation of telomerase. Telomerase is a ribonucleoprotein reverse transcriptase enzyme, consisting of a catalytic subunit (TERT), associated template RNA and structural proteins. The enzyme activity compensates for the loss of telomeric DNA by adding repeat sequences to the chromosome ends. As a result , telomerase acts as a reverse transcriptase that uses part of its intrinsic RNA component as a template for telomeric repeat synthesis.
Numerous data on telomerase expression demonstrate the presence of telomerase activity in the vast majority of different types of cancer, but failed to detect telomerase activity in most normal tissues.