Telomere and telomerase. Illustration showing how the enzyme telomerase (blue) acts on a telomere, the endpoint of deoxyribonucleic acid (DNA) found in chromosomes. The telomere is a region of repeated non-coding nucleotides (green), the function of which is to prevent coding nucleotides being lost during DNA replication. Telomeres shorten over time and this process is thought to play a role in cancer and ageing. Telomerase is a reverse transcriptase that creates the telomere regions using an RNA template (yellow). The nucleotides are A (adenine), C (cytosine), G (guanine), and T (thymine). For this artwork with labels, see C023/8862.