[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.]

During the copying process, a free radical, spun off perhaps by ionizing radiation, strikes the DNA and causes an incorrect pairing of two bases.

[As the base pairs separate, a free radical, shown as a yellow ball, comes in from the left and strikes a red base on the leftmost blue spiral of the DNA helix. After the free radical strikes, the red base changes color and shape from a pointed red cylinder to a grey diamond shape. As Messenger RNA, shown as a purple ribbon-like structure, moves in, a large yellow hexagonal node is created to bind with the diamond node].

Had the error not occurred in this particular tumor-suppressor gene, cancer might have been averted because this particular gene helps turn of the cancer process.