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Penn researcher shows that DNA gets kinky easily at the nanoscale

PHILADELPHIA Scientists have answered a long-standing molecular stumper regarding DNA: How can parts of such a rigid molecule bend and coil without requiring large amounts of force? According to a team of researchers from the United States and the Netherlands, led by a physicist from the University of Pennsylvania, DNA is much more flexible than previously believed when examined over extremely small lengths. They used a technique called atomic force microscopy to determine the amount of energy necessary to bend DNA over nano-size lengths (about a million times smaller than a printed letter).

The findings, which appear in the November issue of the journal Nature Nanotechnology, illustrate how molecular properties often appear different when viewed at different degrees of magnification.

"DNA is not a passive molecule. It constantly needs to bend, forming loops and kinks, as other molecules interact with it," said Philip Nelson, a professor in Penn's Department of Physics and Astronomy in the School of Arts and Sciences. "But when people looked at long chunks of DNA, it always seemed to behave like a stiff elastic rod."

For example, DNA must wrap itself around proteins, forming tiny molecular structures called nucleosomes, which help regulate how genes are read. The formation of tight DNA loops also plays a key role in switching some genes off. According to Nelson, such processes were considered a minor mystery of nature, in part because researchers didn't have the tools of nanotechnology to examine molecules in such fine detail.

"Common sense and physics seemed to tell us that DNA just shouldn't spontaneously bend into such tight structures, yet it does," Nelson said. "In the conventional view of a DNA molecule, wrapping DNA into a nucleosome would be like bending a yardstick around a baseball."

To study DNA on the needed short length scales, Nelson and his colleagues used a technique called high-resolution atomic force micr
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Contact: Greg Lester
glester@pobox.upenn.edu
215-573-6604
University of Pennsylvania
3-Nov-2006


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