Lab Notes

What are telomeres?

by Patricia Shelton, MD

A telomere is a cap on the end of a chromosome.  The discovery of telomeres was so important to science and medicine that the 2009 Nobel Prize was awarded to three scientists who made the initial discoveries in the field1.  To understand why telomeres are critical, it helps to have a little background in genetics.


The information that dictates the structure and function of the human body is stored in DNA.  Similar to the way that computers store a lot of complex information digitally as 1s and 0s, DNA stores the information that creates your body in the form of four letters: A, T, G, and C.  (They aren’t literally letters, but four slightly different chemicals whose names start with those letters.)  These letters are arranged in specific patterns on long strands of DNA.  Because there’s a lot of information needed to create and maintain a human body, the strands of DNA are very long, so the cell packages them, winding them tightly into structures called chromosomes.


It’s important that the information on the DNA is protected.  If it’s damaged, the cell could malfunction.  It might die, or worse, it might transform into a cancer cell.  The ends of the DNA are vulnerable, and so the last part of the DNA strand consists of the cap called a telomere, which is simply a long series of repeats of a sequence (TTAGGG)2.  It protects the end of the DNA much like the plastic cap on the end of a shoelace.  If a few copies of the repeated sequence are lost, that won’t affect the information encoded on the DNA strand.


When a cell divides, as most types of cells do periodically in order to replace lost or damaged cells, the DNA must be copied accurately, so that each new cell has a complete copy of the necessary information.  However, the enzymes that copy the DNA have a flaw; they can’t copy the very end of a chromosome.  This means that each time the cell divides, the telomeres get a little bit shorter.  Eventually, the telomeres are gone, and the cell could start to lose critical information.  Because of the risk of the cell becoming a cancer cell, the cell actually commits suicide when it detects that its telomeres are too short, to protect the rest of the body from it becoming malignant3.


Thus, telomeres act like a clock of aging.  Looking at the overall population, the average length of telomeres gets slightly shorter each year4.  However, there are individual differences in how quickly telomeres get shorter; those whose bodies are better able to maintain telomere length are likely to have longer lifespans than those whose telomeres shorten more quickly5.





1Gilson E, Segal-Bendirdijan E. The telomere story of the triumph of an open-minded research. Biochimie. 2010 Apr;92(4):321-6.


2Moyzis RK, Buckingham JM, Cram LS, et al. A highly conserved repetitive DNA sequence, (TTAGGG)n, present at the telomeres of human chromosomes. Proc Natl Acad Sci U S A. 1988 Sep;85(18):6622-6.


3Fyhrquist F, Saijonmaa O. Telomere length and cardiovascular aging. Ann Med. 2012 Jun;44 Suppl 1:S138-42.


4Henriques CM, Ferreira MG. Consequences of telomere shortening during lifespan. Curr Opin Cell Biol. 2012 Dec;24(6):804-8.



5Tedone E, Arosio B, Gussago C, et al. Leukocyte telomere length and prevalence of age-related diseases in semisupercentenarians, centenarians and centenarians’ offspring. Exp Gerontol. 2014 Jun 27;58C:90-95.