Telomeres are repetitive nucleotide sequences at the end of each chromatid that protect the chromosomes from deteriorating or fusing with other chromosomes.
When chromosomes are replicated, the chromosome ends shorten due to the synthesis of Okazaki fragments on the lagging strand. The telomeres at the ends of the chromosomes ensure that this shortening process does not result in the degradation of genes near the ends of the chromosomes. Even though telomeres shorten over time they are, in certain cases, replenished by the reverse transcriptase enzyme telomerase.
As shortening of telomeres are linked to ageing, their shortening has also been linked with age-related and deteriorative diseases. Good lifestyle choices and activity have been shown to slow the rate of telomere shortening, reducing the chance of developing age-related diseases.