What is a Telomere?:
A chromosome is a long strand of DNA. At the end of a chromosome is a telomere, which acts like a bookend. Telomeres keep chomosomes protected and prevent them from fusing into rings or binding with other DNA. Telomeres play an important role in cell division.
What Happens When a Cell Divides?:
Each time a cell divides, the DNA unwraps and the information in the DNA is copied. The process does not copy all of the DNA information - the telomeres are not copied. When the cell is finished dividing, the DNA comes back together. The telomeres lose a little bit of length each time this happens.
Why Do They Get Shorter?:
When a cell divides and copies DNA, the strands of DNA get snipped to enable the copying process. The places that are snipped are the telomeres. Since the telomeres do not contain any important information, more important parts of the DNA are protected. The telomeres get shorter each time a cell divides, like a pencil eraser gets shorter each time it's used.
Can Telomeres Become Too Short?:
Yes. When the telomere becomes too short, essential parts of the DNA can be damaged in the replication process. Scientists have noticed that cells stop replicating when telomeres are shorter. In humans, a cell replicates about 50 times before the telomeres become too short. This limit is called the Hayflick limit (after the scientist who discovered it).
How Does All This Affect Aging?:
Researchers can use the length of a cell's telomeres to determine the cell's age and how many more times is will replicate. This is important in anti-aging research. When a cell stops replicating, it enters into a period of decline known as "cell senescence," which is the cellular equivalent of aging. However, another reason telomeres are important is cancer.
Cancer? Why Are We Talking About Cancer Now?:
Cancer is a condition in which certain cells in your body stop dying. Every system in your body is carefully balanced to allow for cells replicating and dying. If cells stop dying and keep replicating, the balance is disrupted and there are too many of one kind of cell. Groups of these cells form tumors. Researchers believe that cancer cells are creating an enzyme called telomerase, which prevents telomere shortening.
Where Does Telomerase Come From?:
Every cell in your body has the genetic code to make telomerase, but only certain cells need to produce this enzyme. White blood cells and sperm cells, for example, need to have telomere shortening switched off in order to make more than 50 copies of themselves through your lifetime. In advanced cancer, the cancer cells also seem to be producing telomerase, which allows them to continue to replicate without dying.
Source: Aging Under the Microscope; National Institutes of Health, National Institute of Aging.
Aging Under the Microscope; National Institutes of Health, National Institute of Aging.