Telomeres are the "caps" that protect the ends of DNA strands from being destroyed by a cell. They are made up of areas of repeated DNA sequences combined with specific proteins at the ends of chromosomes — the tightly wound structures of DNA and proteins inside cells. Telomeres play a role in how fast cells age, though exactly how isn't totally clear.

Organisms without circular chromosomes — including humans, other animals, plants and even single-celled protists — have telomeres. Telomeres act as barriers, preventing DNA from being degraded and corrupted.

If our cells did not have telomeres, cellular machinery "would chew away the ends of the chromosomes and into essential genes," said Jan Karlseder, a professor at the Salk Institute for Biological Studies in California and the director of the Glenn Center for Biology of Aging Research at the Salk Institute. The cell might also attach the end of one chromosome to the end of another, which he said would be "a disastrous event" for a cell.

"Since our chromosomes are linear pieces of DNA, a structure called the telomere has evolved that protects the natural ends of the chromosomes from being recognized as DNA damage," Karlseder told Live Science.

Each time a cell divides, some part of the repeating sequence in a telomere is lost. When telomeres become too short to function effectively, a cell either dies or stops dividing. So because most cells cannot regenerate their telomeres, they become shorter as people age. The rate at which telomeres shorten has also been associated with rates of aging.