A team of theoretical physicists at the University of Manitoba has developed a new model for how an electrical charge travels through DNA. Their research was published earlier this month in Physical Review Letters, the journal of the American Physical Society.

The team’s leader is physicist Tapash Chakraborty, Canada Research Chair in nanoscale physics. He said scientists have been wrestling with the problem of charge migration in DNA since the double helix was discovered more than half a century ago.

“DNA is a fascinating, very intelligent molecule,” he said. “It can self assemble, and with the recent developments in nanotechnology, there is a great deal of interest in its potential use as a molecular wire.”

Researchers around the world have conducted a wide range of studies on the conductive properties of DNA. Some have found it to be highly metallic, while others found the molecule behaved like a semi-conductor.

“The results depend on whether the DNA is wet or dry, or whether it’s a single strand or a rope, so it can be very complicated,” Chakraborty said.

Previous research has shown that of the four bases that make up DNA – adenine, thymine, guanine and cytosine – guanine has the lowest ionization potential, meaning that it’s easier to knock an electron off guanine. When this is done, a positively-charged guanine “hole” will move along the DNA strand until it reaches a “trap” made up of two or three non-charged guanines in a row. The other DNA bases act as barriers to this movement, but the hole can pass through them thanks to a quantum mechanical process called “tunneling.”

Earlier models suggested that when the hole encounters several barriers, it stops tunneling through them and begins to hop along the DNA strand. Unfortunately, this theory didn’t explain some of the experimental results. Chakraborty’s team suggested that since DNA is a double helix, the charge would more likely move over to the other strand and keep going.

“We said the charge could either move along the same strand or it can cross over to the other one, which we think is a more natural model,” Chakraborty said. “We call it a ‘multi-channel tunneling’ model, in which the charge can tunnel all the way through to the trap, taking the path it finds easiest, and that could mean crossing over to the other strand.”

Knowing whether DNA will conduct a charge is of more than just academic interest. Understanding exactly how a charge travels through DNA is very important to rapidly growing fields like nanotechnology, and it also has significant implications for medical research, particularly in understanding the process of DNA damage.

“It is well known that aging, many types of human cancer, and several degenerative neurological diseases are caused by mutations that happen when this DNA base, guanine, is oxidized,” Chakraborty said. “It’s very important to understand how this oxidative damage happens, and what physicists and chemists are doing, in the process of understanding how charges propagate, is describing the electronic properties of these mutational hotspots.”