Telomerase active site bound to DNA, molecular model. Telomerase is a reverse transcriptase that creates telomere regions on DNA (deoxyribonucleic acid) using an RNA (ribonucleic acid) template. Here, telomerase (red, orange, yellow and white) is shown with associated proteins (ribbons): TAP-82 and TAP-50. The RNA template for the elongation of the telomeric DNA of this ribonucleoprotein is shown with the nucleotide bases as ball-and-stick models and the growing DNA in the active centre shown as space-filled spheres. A telomere is the endpoint of deoxyribonucleic acid (DNA) found in chromosomes. Telomeres shorten over time and this process is thought to play a role in cancer and ageing.