Telomerase

Whenever DNA replicates, a little is removed from the end, like a photocopy that was not aligned correctly. Telomerase adds a little to the end of the DNA, in a line of useless letters reading TTAGGG that the DNA can lose without a loss of functions within the cell. A good animation of how this occurs is posted bellow under the For Further Information, Try: tab that I highly recommend seeing.

-bexchada