with every mitotic division telomeric sequences had been shortened and telomerase enzyme added sequences to the end of chromosomes due to its structure that contain RNA short strand that act as a template for reverse transcription of DNA from RNA therefore it is a nucleoprotein in its structure and responsible to recover the chromosomal telomere structure threfore it is very important enzyme and its activity in specialized cell very low while in stem cells and non specialized cell very high also many researcher found that its activity in the cancer cell was very high that called immortal cells