Mysterious electron "holes" trek along our DNA, creating possible mutations as they travel. Researchers have suspected that these holes exist in connection to a single "rung" of the DNA ladder, but in a paper published in the Proceedings of the National Academy of Sciences, Esther Conwell, professor of chemistry at the University of Rochester, has shown that these holes may actually spread themselves across several rungs, with implications for how mutations may arise in our DNA.
"We're starting to understand how DNA functions right down to the quantum level," says Conwell. "These findings show that the current view of electron transport in our DNA may not be accurate, and that another model that takes into account the water and ions surrounding the DNA, solves the puzzle better."
These holes are created when an electron is removed from a strand of DNA. That can happen in a number of ways, such as an X-ray streaking through the DNA molecule and knocking out an electron. If the electron were removed from a base pair—a rung of the DNA molecule—its absence would result in an electrical charge, equal to the negative charge on the electron, but positive, in that part of the molecule. The charge could wander among the base pairs, carrying an electric current. Alighting on one type of base, guanine, can cause it to chemically react with water, damaging the structure of the DNA and giving rise to possible harmful mutations.
Although many researchers believed these holes would be localized, meaning occupying a single bases pair or rung, Conwell realized that the delocalized picture is the more likely one. In quantum mechanics, a particle like an electron can be present in a sort of blur of existence, rather than in a single position. It's as if the electron were cloud-like, having a definite presence and center, but not entirely present at any single point. The same goes for the absence of an electron, and this is what Conwell's research suggests—that electrons' absences are spread out across several DNA base pairs, not concentrated as single points on individual pairs.
In the new findings, Conwell shows that the delocalized model explains many experimental results for hole movement in DNA that had not been successfully explained with the localized model. Recent experiments by J. K. Barton of the California Institute of Technology and her group showed that holes in DNA are indeed delocalized over about four bases, in agreement with the results of the calculations of Conwell's group.
"Beyond understanding our DNA and the possible medical benefits of such research, there are efforts under way to utilize these electron holes to turn strands of DNA into tiny electrical conductors that are parts of tiny circuits," says Conwell. "With suitable contacts to the DNA introducing electrons or holes at one end, and removing them at the other end, it's possible to have DNA transistors smaller than we can manufacture today."
Conwell received national attention in 2002 when she was named one of the top 50 most important women in science by Discover magazine for revealing how electronic signals flow through semiconductors, a technology that helped lead to the computer revolution. Her research, exploring how electric fields affect the movement of electrons in semiconductors, earned her an uncommon dual membership in the National Academy of Sciences and the National Academy of Engineering, two of the highest honors a scientist or engineer can receive.