[Animation clip begins by zooming in on a vertically oriented DNA helix set on an empty black background. The helix is comprised of two ribbon-like vertical spiraling blue structures, each of which has a series of colored rungs running its entire length. The rungs, or bases, which extend horizontally from each spiral, are red, yellow, green and purple. The bases on one spiral are bound to those on the other, creating horizontal base pairs that connect the two spirals. The base pairs are matched by color: red/green and yellow/purple. The bases are also shaped differently, so that a red base fits exclusively into a green base and a purple base fits exclusively into a yellow base.]

Changes in DNA, some of which are inherited, others of which are due to outside causes, can lead to cancer. The cancer process begins when a cell starts to divide.

[Zoom in on DNA helix]

In division, the DNA begins to unwind [Base pairs begin to separate, unwinding the DNA helix] and a strand of what's called Messenger RNA begins to copy one of the DNA strands [Messenger RNA, shown as a spiraling ribbonlike purple structure, creates matching base pairs on half of the DNA helix].

If the copying process goes wrong, cancer can occur.