DNA Molecular Stretching is Studied
Posted on: Tuesday, 8 August 2006, 12:00 CDT
Scientists at the U.S. Department of Energy's Lawrence Berkeley Laboratory have discovered when a DNA molecule is stretched, it begins to overwind.
Biologists have long believed as DNA is stretched, its double helix starts to unwind. But now the Berkeley Lab researchers have proven that theory to be at least partly incorrect.
The scientists used a combination of microscopic beads and magnetic tweezers to observe that when a DNA molecule is stretched, it begins to overwind until the force being applied to stretch the DNA exceeds about 30 picoNewtons -- one picoNewton is about a trillionth the force required to hold an apple against Earth's gravity.
Beyond the 30 picoNewton threshold, the DNA double helix begins to unwind in accordance with predictions.
DNA's helical structure implies that twisting and stretching should be coupled, hence the prediction that DNA should unwind when stretched, said biophysicist Carlos Bustamante, who led the experiment. That is why it was such surprise when we directly measured twist-stretch coupling to find, instead, DNA overwinds when stretched. The DNA molecule, when studied at close range, continues to surprise us!
The research is detailed in the journal Nature.
Source: United Press International
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