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Images of supercoiled DNA show complex, dynamic structure

"Our study looks at DNA on a somewhat grander scale," said researcher Sarah Harris.

By Brooks Hays

LEEDS, England, Oct. 13 (UPI) -- Everyone knows the double helix, the iconic double-stranded molecules of DNA, but new research suggests the image is a simplified approximation.

In reality, supercoiled DNA is much more complex and dynamic.

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Using high-tech microscopy, researchers at Baylor College of Medicine, in Texas, captured high-resolution 3-D images of supercoiled DNA. The images were analyzed by scientists at the University of Leeds, in England.

Instead of zooming in on the DNA, scientists took a wide-angle view. The new perspective revealed a varied and complex design. More than just a twisting double-helix, researchers found a whole range of dynamic shapes and structures -- figure eights, handcuffs, circles, pretzel twists.

That DNA would take on a variety of complex twists, turns and coils isn't all that surprising. A complete DNA set comprises 3 billion base pairs. Stretched to full length, a DNA sequence measures more than 39 inches. To fit inside the nucleus of a cell, it has to bunch and coil itself in dramatic fashion.

Researchers didn't attempt to look at all 3 billion pairs, just a few hundred. Still, the grander view revealed DNA's propensity for dynamic design.

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"When Watson and Crick described the DNA double helix, they were looking at a tiny part of a real genome, only about one turn of the double helix," Sarah Harris, a researcher at Leeds' School of Physics and Astronomy, said in a press release. "This is about 12 DNA 'base pairs,' which are the building blocks of DNA that form the rungs of the helical ladder."

"Our study looks at DNA on a somewhat grander scale -- several hundreds of base pairs -- and even this relatively modest increase in size reveals a whole new richness in the behavior of the DNA molecule," Harris added.

Harris and her colleagues detailed their findings in a new paper, published online this week in the journal Nature Communications.

The researchers hope that by better understanding DNA structure inside cells, they can improve the computer models that design medicine -- like new antibiotics or chemotherapies.

"This is because the action of drug molecules relies on them recognising a specific molecular shape -- much like a key fits a particular lock," Harris said. "We are sure that supercomputers will play an increasingly important role in drug design. We are trying to do a puzzle with millions of pieces, and they all keep changing shape."

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