[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 bases fits exclusively into a green base and a purple bases fits exclusively into a yellow base.]

[Zoom in on a group of base pairs in the DNA helix. As the base pairs separate, Messenger RNA, shown as a purple ribbon-like structure, moves in and creates matching base pairs on half of the helix. But one of the pairs, a green node with a purple node, is mismatched by color and shape.]

A mismatch of base pairs, shown here as a green base pairing with a purple base instead of a proper yellow/purple pairing, can occur during the DNA copying process.

A mismatch repair gene then might signal a protein to help repair the process [A mismatch repair gene, shown as a purple net-like structure, comes in from the left and settles on the mismatched base pair].

But before the repair process can be completed, an outside agent, such as the chemical benzene, interferes and defeats the repair, leading to a cancerous cell.

[The mismatched green base begins to turn yellow. A group of oblong yellow hexagons with brown circular centers comes in from the right and swarms around the group of base pairs. The mismatch repair gene moves out to the right and the mismatched base returns to its original green color].