Telomeres shorten each time a cell
divides. In most cel s, the telomeres
becomes too short, it can no longer protect the cell’s
eventual y reach a critical length
DNA, leaving the cell at risk for serious damage. In
when the cel s stop proliferating and
most cells, telomere length cannot be restored. Extreme
become senescent.
telomere shortening triggers an SOS response, and
But, in certain cel s, like sperm and egg
the cell will do one of three things: stop replicating
cel s, the enzyme telomerase restores
by turning itself off, becoming what is known as
telomeres to the ends of chromo-
senescent; stop replicating by dying, called apoptosis;
somes. This telomere lengthening
or continue to divide, becoming abnormal and poten-
insures that the cel s can continue to
tially dangerous (for example, leading to cancer).
safely divide and multiply. Investiga-
Scientists are interested in senescent cells because,
tors have shown that telomerase is
although they are turned off, they still work on many
activated in most immortal cancer
levels. For instance, they continue to interact with
cel s, since telomeres do not shorten
other cells by both sending and receiving signals.
when cancer cel s divide.
However, senescent cells are different from their
earlier selves. They cannot die, and they release