How does a cell know how old it is?Every time a cell multiplies to make two new cells, special zones at the ends of its chromosomes, called telomeres, become shorter. Once the telomeres reach a certain length, the cell stops dividing and eventually dies. The only cells to escape this fate are those that divide to make eggs and sperm. In these cells, a substance called telomerase builds the telomeres up again, so they remain the same length.
Telomerase - an elixir of life?
Scientists have made normal cells in a test tube multiply indefinitely by adding telomerase. Some have claimed that telomerase could be used as an 'elixir of life', but this is unlikely. Apart from germ cells, the only other cells that can multiply indefinitely are cancer cells. Allowing old, damaged cells to carry on growing and dividing forever would probably have disastrous results.