Telomerase

Telomerase is an enzyme that preserves the ends of eukaryotic chromosomes, preventing their shortening, through the synthesis of telomeric repeat sequences. This is a ribonucleoprotein since it is composed of an RNA subunit (hTR or hTERC) and a protein subunit (hTERT) – catalytic part (reverse transcriptase acting on the 3 'end of the DNA chain). It has its own mold (template) of DNA. The RNA portion of human telomerase has approximately 450 nucleotides and the mold region, containing eleven, is complementary to the telomeric sequence 5’-TTAGGG-3’. In all organisms, the produced sequence is rich in guanine.
That enzyme is active only in stem cells, breeding and embryonic, it is also found in cancerous cells. In the latter case, the telomerase activation occurs unusual and uncontrollably. Since prevents shortening of telomeres allows cells to divide an infinite number of times without loss of genetic information, conferring immortality to them.
The telomerase enzyme is considerate a biologic clock, a marker indicating that cellular senescence will inevitably be installed, causing aging in cells that exhibit telomerase activity.