Telomeres - the giver of life and death

Telomeres are extra chunks of DNA at the ends of chromosomes that protect important segments of DNA from being lost during cell replication and division. As a cell keeps replicating, the telomeres become shorter. Once the telomere is gone, the cell stops dividing and becomes senescent before it eventually dies. Telomeres can be extended by the enzyme telomerase, which results in cell immortality as long as the telomerase is still functioning. This enzyme is present in immortal cells such as germ cells and stem cells. Additionally, telomerase is over-expressed in cancer cells, which is one of the many reasons why they are able to replicate uncontrollably. 

Telomerase was only discovered within the past 50 years, so details about its structure, function, and expression, among others, is still being researched or recently found. For example, ATM kinase has been known to be involved in DNA repair, but now researchers found that it is also involved in the elongation of telomeres. Getting to know how each enzyme and other proteins are involved in this process could allow them to be manipulated, such as shutting down elongation in cancerous cells or stimulating telomere elongation in aging cells. However, there is a delicate balance between elongating telomeres for longer-life spans/anti-aging and keeping them at a controlled length so that the cells don't become cancerous and have the opposite effect (i.e., death).

Reference:
Another Telomere-Regulating Enzyme Found