Adjust the length of telomeres is crucial in the process of senescencji cell immortalization and tumorigenesis . It occurs mainly due to the activity of telomerase . Telomerase is a DNA polymerase -dependent RNA specific for telomeric sections , which plays a crucial catalytic subunit hTERT (reverse transcriptase ) necessary for enzyme activity. The function of telomere - telomerase has been demonstrated in most tumor cells , stem cells and lymphocytes during differentiation and activation.