Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

New look at DNA hints at origin of ultraviolet damage

25.08.2005


Chemists at Ohio State University have gained new insight into how sunlight affects DNA. And what they found overturns ideas about genetic mutation that originated decades ago.



In the current issue of the journal Nature, Bern Kohler and his colleagues report that DNA dissipates the energy from ultraviolet (UV) radiation in a kind of energy wave that travels up the edge of the DNA molecule, as if the energy were climbing one side of the helical DNA “ladder.”

The finding lends insight into how DNA damage occurs along the ladder’s edge.


It also counters what scientists proposed in the 1960s: that UV causes mutations by damaging the bonds between base pairs – the horizontal “rungs” on the ladder. The new study shows that UV energy moves vertically, between successive bases.

In undamaged DNA, there are no chemical bonds between vertically stacked bases. But the bases do interact electronically, which is why Kohler thinks they form an efficient conduit for UV energy to flow through.

“Even though paired bases are connected by weak chemical bonds, it’s the interactions that take place without chemical bonds – the interactions between stacked bases – that are much more important for dissipating UV energy,” Kohler said.

The Nature paper builds on work from five years ago, when the associate professor of chemistry and his team first discovered that single DNA bases convert harmful UV energy to heat to prevent sun damage in the same way that sunscreen molecules protect sunbathers.

Back then, they studied only single bases floating in water. They hit the bases with a kind of UV strobe light, and saw that the energy was released as heat in less than one trillionth of a second.

Their new experiments show that the behavior of full DNA differs profoundly from that of isolated bases. When the chemists turned their strobe light on whole strands of novel DNA, the UV energy still changed to heat eventually, but the energy dissipated a thousand times more slowly.

That’s an eternity in the DNA universe, where scientists need to use special equipment just to see these ultra-fast chemical reactions happen. Yet, Kohler’s team saw no evidence that the UV affected the chemical bonds between the base pairs. They surmised that the UV energy was leaving the molecule by traveling along the edges instead.

“This slow relaxation of energy is utterly different from the mechanism in single bases that transforms the energy into heat in less than a trillionth of a second,” Kohler said.

“Eventually, the energy does turn into heat, but the important point is that the energy is retained within the molecule for much longer times,” he added. “This can cause all kinds of photochemical havoc.”

It could be that when base pairs are aligned in their natural state in a DNA strand, the electronic interactions along the stack provide an easier way for DNA to rid itself of UV energy, compared to passing the energy back and forth between the two bases in a base pair as scientists have previously thought.

In fact, it was the brilliance of James Watson and Francis Crick’s discovery of the structure of DNA that kept this secret hidden for so many years, Kohler said. Their work revealed that the DNA helix was composed of paired bases, and that discovery led researchers to focus on how UV energy might interact with base pairs.

“In fact, so much attention has been paid to base pairing that this other interaction, base stacking, has been neglected,” Kohler said.

Base stacking is frequently overlooked, he admitted, because the ladder terminology that we use to describe DNA structure makes us think that there are open spaces between successive rungs of base pairs.

A better analogy would be a stack of coins, he said. Bases are stacked right on top of each other.

Here’s what he and his team suspect is happening during the UV energy wave: as sunlight warms our skin, UV photons are absorbed by the bases, causing their electrons to vibrate. These high-energy vibrations nudge the atoms in the bases around, but only along one edge of the DNA ladder at a time.

If all goes well, the DNA returns to normal after the energy wave passes. But some of the time, the atoms don’t return to their original positions, and new chemical bonds are formed.

Scientists know that such accidental bonds create “photolesions” – injuries that prevent DNA from replicating properly. The details of the process aren’t fully understood, but studies suggest that photolesions cause genetic mutations that lead to diseases such as cancer.

This new research helps explain why most photolesions are formed between bases on the same side of the DNA strand.

Scientists believe that proteins in the body repair DNA by removing photolesions and filling in new material, using the remaining DNA strand as a template.

If UV damage is confined to one side of the DNA double helix or the other, then the undamaged side makes an easy template for the proteins to follow. But if both sides of a strand were damaged, then the template would effectively be missing.

The Nature paper highlights the shortcomings of previous studies, which applied results from isolated base pairs to the full DNA molecule. “It turns out that you can’t extrapolate the results of base pairs to whole strands of DNA,” Kohler said.

The discovery has clear implications for biology, since it can help explain the DNA repair process.

“The ability to observe what happens to electronic energy in DNA on such short time scales also extends the hope that methods such as ours can finally determine how DNA is damaged by UV light in the first place,” Kohler said.

The Ohio State chemists are now testing other DNA strands. For simplicity, they first wanted to compare the behavior of single Adenine and Thymine bases with strands entirely composed of those two bases. That is the work described in Nature.

Kohler’s team includes Carlos E. Crespo-Hernández and Boiko Cohen, both postdoctoral researchers in the Department of Chemistry at Ohio State. Their work was sponsored by the National Institutes of Health and the Alexander von Humboldt Foundation, and was performed at Ohio State’s Center for Chemical and Biophysical Dynamics, which is funded by the National Science Foundation.

Bern Kohler | EurekAlert!
Further information:
http://www.osu.edu

More articles from Life Sciences:

nachricht Could this protein protect people against coronary artery disease?
17.11.2017 | University of North Carolina Health Care

nachricht Microbial resident enables beetles to feed on a leafy diet
17.11.2017 | Max-Planck-Institut für chemische Ökologie

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: A “cosmic snake” reveals the structure of remote galaxies

The formation of stars in distant galaxies is still largely unexplored. For the first time, astron-omers at the University of Geneva have now been able to closely observe a star system six billion light-years away. In doing so, they are confirming earlier simulations made by the University of Zurich. One special effect is made possible by the multiple reflections of images that run through the cosmos like a snake.

Today, astronomers have a pretty accurate idea of how stars were formed in the recent cosmic past. But do these laws also apply to older galaxies? For around a...

Im Focus: Visual intelligence is not the same as IQ

Just because someone is smart and well-motivated doesn't mean he or she can learn the visual skills needed to excel at tasks like matching fingerprints, interpreting medical X-rays, keeping track of aircraft on radar displays or forensic face matching.

That is the implication of a new study which shows for the first time that there is a broad range of differences in people's visual ability and that these...

Im Focus: Novel Nano-CT device creates high-resolution 3D-X-rays of tiny velvet worm legs

Computer Tomography (CT) is a standard procedure in hospitals, but so far, the technology has not been suitable for imaging extremely small objects. In PNAS, a team from the Technical University of Munich (TUM) describes a Nano-CT device that creates three-dimensional x-ray images at resolutions up to 100 nanometers. The first test application: Together with colleagues from the University of Kassel and Helmholtz-Zentrum Geesthacht the researchers analyzed the locomotory system of a velvet worm.

During a CT analysis, the object under investigation is x-rayed and a detector measures the respective amount of radiation absorbed from various angles....

Im Focus: Researchers Develop Data Bus for Quantum Computer

The quantum world is fragile; error correction codes are needed to protect the information stored in a quantum object from the deteriorating effects of noise. Quantum physicists in Innsbruck have developed a protocol to pass quantum information between differently encoded building blocks of a future quantum computer, such as processors and memories. Scientists may use this protocol in the future to build a data bus for quantum computers. The researchers have published their work in the journal Nature Communications.

Future quantum computers will be able to solve problems where conventional computers fail today. We are still far away from any large-scale implementation,...

Im Focus: Wrinkles give heat a jolt in pillared graphene

Rice University researchers test 3-D carbon nanostructures' thermal transport abilities

Pillared graphene would transfer heat better if the theoretical material had a few asymmetric junctions that caused wrinkles, according to Rice University...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Ecology Across Borders: International conference brings together 1,500 ecologists

15.11.2017 | Event News

Road into laboratory: Users discuss biaxial fatigue-testing for car and truck wheel

15.11.2017 | Event News

#Berlin5GWeek: The right network for Industry 4.0

30.10.2017 | Event News

 
Latest News

NASA detects solar flare pulses at Sun and Earth

17.11.2017 | Physics and Astronomy

NIST scientists discover how to switch liver cancer cell growth from 2-D to 3-D structures

17.11.2017 | Health and Medicine

The importance of biodiversity in forests could increase due to climate change

17.11.2017 | Studies and Analyses

VideoLinks
B2B-VideoLinks
More VideoLinks >>>