DNA’s famous helical structure has an unexpected twist. It turns out that tightly winding the molecule’s double helix makes it stretch, and untwisting it makes it shrink.
Timothée Lionnet at the French National Centre for Scientific Research (CNRS) in Paris tethered one end of a DNA molecule to a microscope slide, and the other to a magnetic bead, which he rotated with a magnetic field, twisting the helix.
“We expected the DNA to shorten, but it didn’t,” says Lionnet. The strand lengthened by 0.42 nanometres for every extra turn that was introduced (www.arxiv.org/abs/q-bio.BM/0602008v1).
Winding up DNA brings the…
