DNA

Splashery stretches a drumhead over this Splash's outline, twelve inches across, and finds the ways it can ring. Its lowest is 1670.5 Hz, 410 cents sharp of E6, the nearest tine on the comb. The next fifteen are its overtones, and each one draws its own figure: sand gathers on the lines that stay still.

Tap it to unzip it and zip it back up.

DNA is the long molecule that carries the instructions for building and running a living thing. It is shaped like a twisted ladder, a double helix: two strands wind around each other, joined by pairs of bases, A with T and C with G, like the rungs.

Tap it and it unzips almost to the bottom, the bases lighting up in pairs as it opens, then zips back up. A cell unzips its DNA like this to copy it. In 1953 scientists worked out its shape, helped by Rosalind Franklin's X-ray pictures. The DNA in a typical human cell with a nucleus would stretch about 2 meters if pulled straight. Partner sets the matching strand's color.

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