Cellular Aging: Telomeres

Telomeres are specialized structures present at the end of liner chromosomes; they serve the essential function of protecting and stabilizing chromosome ends. The telomere was first defined in the 1930s following observations that naturally occurring chromosome ends behave differently than chromosome breaks induced by damaging agents such as ionizing radiation. Both structures are ends of double-stranded DNA molecules. However, chromosome ends are stable, allowing accurate transmission of chromosomes from generation to generation without loss of genetic material, whereas induced breaks are very unstable, reacting with other chromosomes in the cell to create rearrangements and chromosome fusions. In addition, broken ends of DNA trigger cellular protective responses. These responses act either to allow the DNA damage to be repaired, or to remove the cell from the population by cellular suicide, called apoptosis. Even though telomeres are the physical end of a DNA molecule, they do not trigger these protective responses. These observations indicated that there is something special about naturally occurring chromosome ends.