Telomere

Human chromosomes (grey) capped by telomeres (white)

A telomere is a region of DNA at the end of a chromosome. It protects the end of the chromosome from deteriorating (getting worse) or fusing (joining) with other chromosomes.

The telomeres are made of repeated sequences of DNA ('repetitive DNA'). During cell division, enzymes that duplicate DNA cannot continue their work all the way to the end of chromosomes. If cells divided without telomeres, they would lose the ends of their chromosomes, and the information they contain.

The telomeres are disposable buffers blocking the ends of the chromosomes. They are destroyed during cell division, and are remade by an enzyme, telomerase reverse transcriptase.

The Australian Elizabeth Blackburn and the Americans Carol Greider and Jack Szostak won the 2008 Nobel Prize in Physiology or Medicine for their work on telomeres.

Telomere Media

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  Lagging strand during DNA replication

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  Shelterin co-ordinates the T-loop formation of telomeres.

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  Synthesis of chromosome ends by telomerase

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  The average cell will divide between 50 and 70 times before cell death. As the cell divides the telomeres on the end of the chromosome get smaller. The Hayflick limit is the theoretical limit to the number of times a cell may divide until the telomere becomes so short that division is inhibited and the cell enters senescence.