DNA鈥檚 famous helical structure has an unexpected twist. It turns out that tightly winding the molecule鈥檚 double helix makes it stretch, and untwisting it makes it shrink.
Timoth茅e 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.
鈥淲e expected the DNA to shorten, but it didn鈥檛,鈥� says Lionnet. The strand lengthened by 0.42 nanometres for every extra turn that was introduced ().
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Winding up DNA brings the two strands of the molecule closer together, says Richard Lavery, also at CNRS. This forces the base pairs linking the strands to incline, which stretches the molecule. 鈥淭wisting DNA is not as simple as wringing out a cloth,鈥� he says.
