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.
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.
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.
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).
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 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.
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.
Telomere Shortening and Aging
In population level studies, researchers have shown that older people have shorter telomeres. Eventually, the cells with shorter telomeres can no longer replicate and, taken over time and lots of cells, tissue damage and the dreaded “signs of aging” can show up. Most cells can replicate about 50 times before the telomeres are too short. Some believe that telomeres are the “secret to longevity” and there are circumstances in which the telomeres will not shorten. Cancer cells, for example, don’t die (which is the main problem) because they switch on an enzyme called telomerase, which adds to the telomeres when cells divide. Some cells in your body need to do this (stem cells and sperm cells, for example) because they need to replicate more than 50 times in your lifetime.
Does It Happen to Everyone?
No — and that’s a big surprise. Researchers in Sweden found out that some people’s telomeres do not necessarily get shorter over time. In fact, they found that some people’s telomeres even get longer. This variation at the individual level was hidden by prior studies that averaged results over large population.
What Does Non-Shortening Telomeres Mean?
In the study, 959 individuals donated blood twice, 9 to 11 years apart. On average, the second samples had shorter telomeres than the first. However, around 33% of the people had either a stable or increasing telomere length over a period of around 10 years. What does this mean? Nobody knows. It could be that those people have an amazing cellular anti-aging mechanism or it could be that they have an early sign of cancer (researchers tried to rule this out) or it could be fairly meaningless. What we do know for sure is that aging is a lot more complicated than simply looking at the shortening of telomeres.
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