DNA's Dark Side :: Astrobiology Magazine ::

DNA's Dark Side :: Astrobiology Magazine ::

DNA's Dark Side
Summary (Apr 11, 2006): Chemists at Oregon State University have pioneered a controversial theory about how supposedly-stable DNA bases can be pushed into a "dark state" in which they are highly vulnerable to damage from ultraviolet radiation -- an idea that has challenged some of the most basic concepts of modern biochemistry.

based on an Oregon State University release

"But just since last summer this has been a key point of discussion at several conferences and caused quite an excitement, as people see the data," Kong said. "Among other things, it helps to explain how water, or something else serving the same role, could have helped lead to the evolution of life."

The core of the debate, Kong said, relates to the behavior of the nucleic acid bases -- adenine, thymine, guanine and cytosine -- that as A-T and G-C base pairs form DNA and ultimately become the blueprint for all living things. One of the most basic premises of biochemistry is that these nucleic acid bases are very stable, as they would have to be to prevent rampant mutations and make an organized genetic structure possible.

But studies at OSU, which were done with highly sophisticated electron spectroscopy, showed that the alleged stability of the nucleic acid bases in DNA is largely a myth.

This graph shows how quickly ultraviolet (UV) energy deposited in the electrons of a nucleoside is converted to heat, which is then absorbed by water surrounding the nucleoside. Here, time is measured in femtoseconds, or quadrillions of a second. The diagram to the upper right of the image depicts a particular nucleoside -- adenosine. This molecule consists of a UV-absorbing base (shown in red) and a simple sugar (shown in gray) that binds it to the RNA backbone. This base is also found in DNA. Credit: Ohio State University

"In their biological form, surrounded by other hydrogen-bonded bases, it's true that the nucleic acids which make up DNA are stable," Kong said. "But we found that living things, in their totality, provide an environment which creates that stability, through attachments within base pairs and/or with neighboring bases. These attachments allow damaging photonic energy to be released as heat. But a DNA base as an isolated molecule, just by itself, does not have that stability."