After some half a century of scrutiny, you might expect the DNA molecule to have few surprises left in store. But biochemists in California have discovered something quite remarkable about this most familiar of molecules - if you stretch this helical structure, it actually winds itself more tightly.
It sounds counterintuitive, but as Carlos Bustamante and his colleagues report in a paper published online by Nature (Vol. 442, No. 7099), the DNA double helix winds more tightly when gently stretched. Only if you really tug at it does its spiral begin to unfurl. This is in contrast to almost all other helical structures - such as an old-fashioned sweet wrapper, for instance, which unwinds when you pull on its ends.
The researchers made their discovery by studying single DNA
molecules with tiny stretching forces applied to them. The discovery may also explain some puzzling real-life examples of cellular DNA structures that seem to be both taut and yet tightly wound.
Carlos Bustamante (University of California Berkeley, CA, USA)
Article available online.
(C) Nature press release.
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