Researchers at Duke University's Pratt School of Engineering have uncovered a missing link in scientists' understanding of the physical forces that give DNA its famous double helix shape .
The study conducted by Piotr Marszalek, a professor of mechanical engineering at Duke said that the first direct measurements of the forces within single strands of DNA that wind around each other in pairs to form the complete, double-stranded molecules.
"The stability of DNA is so fundamental to life that it's important to understand all factor. If you want to create accurate models of DNA to study its interaction with proteins or drugs, for example, you need to understand the basic physics of the molecule. For that, you need solid measurements of the forces that stabilize DNA," Marszalek said.
Each DNA strand includes a sugar and phosphate "backbone" attached to one of four bases, which encode genetic sequences. The strength of the interactions within individual strands comes largely from the chemical attraction between the stacked bases. But the integrity of double-stranded DNA depends on both the stacking forces between base units along the length of the double helix and on the pairing forces between complementary bases, which form the rungs of the twisted ladder.
According to Marszalek, earlier studies have focused more attention on the chemical bonds between opposing bases, measuring their strength by "unzipping" the molecules' two strands,. Studies of intact DNA make it difficult for researchers to separate the stacking from the pairing forces.
"To get around that problem in the new study, the Duke team used an atomic force microscope (AFM) to capture the "mechanical fingerprint" of the attraction between bases within DNA strands. The bonds within the molecules' sugar and phosphate backbones remained intact and therefore had only a minor influence on the force measurements," Marszalek said.
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