Posted 06-17-2004 at 10:54:08
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>The environment surrounding DNA in living cells plays a surprisingly important role in regulating the movement of electronic charge through the life-coding molecule, suggests a paper published October 19 in the journal Science. The work could lead to a better understanding of how DNA is damaged by oxidative processes and offer clues to potential DNA applications in nanotechnology.
Based on experimental data, computer-based molecular dynamics simulations and complex electronic structure calculations, the paper is the first to describe how sodium ions could control the migration of electron holes -- also known as radical cations -- through DNA. The electron holes, positively charged locations in the DNA structure, are created by normal cellular oxidation processes and everyday events such as exposure to sunlight. Migrating through the DNA to distances up to 30 nanometers from their site of origin, the electron holes ultimately reach certain locations where they may initiate reactions that can damage the genetic coding.
Uzi Landman (left) and Gary Schuster compare results of a molecular dynamics simulation to experimental data. A paper published in the October 19 issue of Science suggests the environment surrounding DNA plays a key role in controlling charge transport.
Photo by Gary Meek (300-dpi JPEG version - 407K)
"Our paper presents a new way of thinking about what controls electrical charge transport in DNA," said Gary Schuster, a professor in the School of Chemistry and Biochemistry at the Georgia Institute of Technology and dean of its College of Sciences. "It is the motions of the water molecules, the sodium ions, the backbone of the DNA and the bases of the DNA that altogether control the movement of charge in the DNA. It's clear that we must consider both the DNA and its environment."
Underlying the charge migration mechanism unveiled in this study are two physical principles: (1) like electrical charges electrostatically repel one another, and (2) thermal energy induces random motion -- known as stochastic dynamic fluctuations -- among the microscopic constituents of matter: ions, atoms and molecules.
In a 1999 paper published in Proceedings of the National Academy of Sciences, Schuster and his colleagues suggested that electrical charge moves through DNA in a "Slinky-like" process in which the molecule distorts itself in an effort to locally stabilize the charge. The new work seeks to explain why the charge moves at all, and to elucidate the dynamical mechanism of long-range transport in DNA.
In a nutshell, the paper's authors argue that the positively charged electron holes -- created by the removal of an electron -- move when approached by positively charged sodium ions hydrated in the aqueous medium surrounding the DNA. Circulated by thermal energy in a random way, the diffusing sodium ions are attracted to specific locations in the DNA, such as the negatively charged