When the DNA "instruction manual" of life becomes damaged – as
it does in human cells tens of thousands of times a day – bad
things can happen. The cell may die, cause an inherited disease,
or grow out of control to form a tumor. To prevent genetic
catastrophe, cells have evolved a molecular toolkit for
repairing their own DNA to restore normal behavior, duplication,
and controlled growth. A cell sensing genetic injury often
grinds to a halt. It puts growth and division on hold and, like
a ship in dry dock, undergoes repairs before setting sail again.
The cell's repair kit – specialized enzymes and other proteins –
can snip out and replace broken stretches of DNA, correct
spelling errors in the genetic code, or simply bypass the
damaged areas. Self-repair is vital to life and health, because
DNA is constantly under attack from internal and external
forces, including tobacco smoke, sunlight, environmental toxins,
and dietary byproducts. But when a patient has cancer, the
repair team becomes the enemy, since mo