By Elizabeth H. Blackburn
Telomeres are protective tips that stabilize the ends of chromosome. The function of telomeres is to allow cells to divide while holding the genetic material intact. Telomeres contain specialized, simple repetitive DNA sequences that, together with their specifically-bound proteins, protect chromosome ends from damage.
Every time cells divide, unless a process of telomeres elongation intervenes, telomeres become shorter and shorter until, eventually, the cells die. Thus a telomeres is analogue to a “fuse” whose length determines the lifespan of cells when the telomeres “fuse” in cells become too short, either loss of cell replenishment capability, or genomic instability (with the concomitant risk of the cell becoming cancerous) can result.
The telomere shortening process can be slowed, prevented or even reversed by the ribonucleoprotein enzyme telomerase. Telomerase rebuilds back the telomeres by adding telomeric DNA to them. By recognizing a worn-down telomere in a cell and elongating it by telomeric DNA addition, telomerase thus can effectively turn back the hands of the ticking clock that would otherwise be counting down the time to when the telomeric “fuse” will become too short and detonate. The degree of telomerase action therefore is a key factor in counteracting telomere shortening.
Telomerase is found in various human cell types. It is a unique reverse transcriptase because although, like the well-known retroviral reverse transcriptase, it has a catalytic protein, telomerase is a ribonucleic acid complex containing an essential, dedicated RNA as well as protein subunits. The RNA of telomerase contains a short sequence that is copied into the telomeric DNA, in addition, this RNA also has evolutionarily conserved structures that are crucial to the enzymatic reaction of telomerase.
In humans, telomerase is often over-activated in malignant cancer cell, contributing to their uncontrolled growth. However, troughout human life, the telomerase in normal cells may become insufficient, because the telomeres often wear down in cells, and telomere in normal cells in uman body has been linked to disease that increase with aging. In fact, through many clinical studies, telomere shortness has emerged as a potential marker for biological aging, because telomere shortness is associated with the major diseases of aging – including cardiovascular disease, cancer, diabetes, disease of poor tissue replenishment and disease of poor immune function, inflammation – and higher risk mortality.
The insight gained from the research in telomere biology are not so much related to people living longer than normal, but rather, relate to the goal of living longer in good health – that is augmenting the so-called “health-span”. Health-span can be contrasted with the term “lifespan”, which only tells one how many years a person live, but does not give information about the quality of live and health during the years a person is alive. Therefore, an important challenge is the application of this growing knowledge of telomeres and telomerase to forestalling some common disease and improving human health.
