Telomeras

Telomeres are the protective caps at the ends of chromosomes. They are composed of repetitive nucleotide sequences and associated proteins. In humans, this sequence is TTAGGG, repeated thousands of times. Telomeres play a crucial role in maintaining the integrity of our genetic material during cell division. Each time a cell divides, a small portion of the telomere is lost. This is because DNA polymerase, the enzyme responsible for DNA replication, cannot fully replicate the very ends of linear chromosomes.

Over time, telomeres shorten, and when they become critically short, the cell can no longer divide and enters a state of senescence or undergoes programmed cell death (apoptosis). This shortening of telomeres is considered a biological clock that contributes to the aging process. However, the enzyme telomerase can counteract this shortening. Telomerase is a reverse transcriptase that adds repetitive DNA sequences back to the telomeres, thus lengthening them. Telomerase activity is typically high in germ cells and stem cells, allowing these cells to divide extensively. In most somatic cells, telomerase activity is very low or absent, leading to telomere shortening. Dysregulation of telomerase activity has been linked to various diseases, including cancer, where cancer cells often reactivate telomerase to achieve immortality.