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Phoenix666 writes:

DNA, our genetic material, normally has the structure of a twisted rope ladder. Experts call this structure a double helix. Among other things, it is stabilized by stacking forces between base pairs. Scientists at the Technical University of Munich (TUM) have succeeded at measuring these forces for the very first time on the level of single base pairs. This new knowledge could help to construct precise molecular machines out of DNA.

[...] Prof. Hendrik Dietz from the Chair of Experimental Biophysics uses DNA as construction material to create molecular structures. Hence, he is greatly interested in gaining a better understanding of this material. "There are two types of interactions which stabilize double helices," he explains. For one, DNA contains hydrogen bonds.

[...] To put it simply, the measurement system is designed hierarchically and involves microscopic beams, at the tips of which one or more double helix structures running in parallel are located. These have been modified such that each end carries one base pair. Two of these microscopic beams are connected with a flexible polymer. On the other side, the beams are coupled to microscopic spheres which can be pulled apart using optical laser tweezers. In solution, the base pairs on the end of one of the beam[s] can now interact with the base pairs on the end of the other beam. This also makes it possible to measure how long a stacking bond between them lasts before they fall apart again, as well as the force acting between the base pairs.

The forces measured by the researchers were in the range of piconewtons. "A newton is the weight of a bar of chocolate," explains Dietz. "What we have here is a thousandth of a billionth of that, which is practically nothing." Forces in the range of two piconewtons are sufficient to separate the bond created by stacking forces.

Furthermore, the scientists also observed that the bonds spontaneously broke up and formed again within just a few milliseconds. The strength and the lifetime of the interactions depends to a great extent on which base pairs are stacked on each other.

An abstract is available — full article is paywalled.

Being able to precisely measure and understand the forces within DNA is key to using organic molecules for nanometer-scale construction. The team in Munich is currently using what they've learned to construct a molecular rotational motor whose movements are controlled by chemical and thermal stimuli.

Original Submission