Genome complexity: DNA u-v light protection (Introduction)

by David Turell @, Saturday, June 24, 2017, 20:16 (732 days ago) @ David Turell

All four DNA code amino acids protect themselves from u-v light. Thiss protects DNA from u-v light damage:

"In experiments at the Department of Energy's SLAC National Accelerator Laboratory, scientists were able to see the first step of a process that protects a DNA building block called thymine from sun damage: When it's hit with ultraviolet light, a single electron jumps into a slightly higher orbit around the nucleus of a single oxygen atom.

"This infinitesimal leap sets off a response that stretches one of thymine's chemical bonds and snaps it back into place, creating vibrations that harmlessly dissipate the energy of incoming ultraviolet light so it doesn't cause mutations.


"Thymine and the other three DNA building blocks also strongly absorb ultraviolet light, which can trigger mutations and skin cancer, yet these molecules seem to get by with minimal damage. In 2014, a team led by Markus Guehr – then a SLAC senior staff scientist and now on the faculty of the University of Potsdam in Germany – reported that they had found the answer: The stretch-snap of a single bond and resulting energy-dissipating vibrations, which took place within 200 femtoseconds, or millionths of a billionth of a second after UV light exposure.

"But what made the bond stretch? The team knew the answer had to involve electrons, which are responsible for forming, changing and breaking bonds between atoms. So they devised an ingenious way to catch the specific electron movements that trigger the protective response.


"For this new experiment, the scientists hit thymine molecules with a pulse of UV laser light and tuned the energy of the LCLS X-ray laser pulses so they would home in on the response of the oxygen atom that's at one end of the stretching, snapping bond.

"The energy from the UV light excited one of the atom's electrons to jump into a higher orbital. This left the atom in a sort of tippy state where just a little more energy would boost a second electron into a higher orbital; and that second jump is what sets off the protective response, changing the shape of the molecule just enough to stretch the bond.

"The first jump, which was previously known to happen, is difficult to detect because the electron winds up in a rather diffuse orbital cloud, Guehr said. But the second, which had never been observed before, was much easier to spot because that electron ended up in an orbital with a distinctive shape that gave off a big signal.

"'Although this was a very tiny electron movement, the signal kind of jumped out at us in the experiment," Guehr said. "I always had a feeling this would be a strong transition, just intuitively, but when we saw this come in it was a special moment, one of the best moments an experimentalist can have."

"Study lead author Thomas Wolf, an associate staff scientist at SLAC, said the results should settle a longstanding debate about how long after UV exposure the protective response kicks in: It happens 60 femtoseconds after UV light hits. This time span is important, he said, because the longer the atom spends in the tippy state between the first jump and the second, the more likely it is to undergo some sort of reaction that could damage the molecule."

Comment: we see plastics denature when outside in sunlight. DNA can do the same, but the amino acids in DNA can respond very quickly. Did God arrange this protection? The only way to look into the point is to test the other 16 essential amino acids in living matter to see if they are as quick in response. By the way the article doesn't mention uracil which is in RNA and probably is just as fast in response.

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