April 11, 2006 | David F. Coppedge

Isolated DNA Bases Are Destroyed Quickly

Without water, DNA bases fall apart quickly.  Any origin-of-life models expecting the building blocks of DNA (nucleotides) to stick around for long are going to suffer, say researchers from Oregon State University.  The molecules can enter a “dark state” in which they are highly vulnerable to UV radiation.  This idea was once considered “scientific heresy” – so much so that the researchers “had a lot of sleepless nights” defending the idea from critics:

The core of the debate, [Wei] Kong [professor of chemistry] said, relates to the behavior of the nucleic acid bases – adenine, thymine, guanine and cytosine – which 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. (Emphasis added in all quotes.)

Isolated DNA bases, in other words, do not have the stability scientists thought they did.  They are extremely vulnerable to UV damage for short periods:

The lifetime of the dark state is not long – a nanosecond is one billionth of a second.  But it’s more than enough time for DNA mutations to happen, Kong said.  And the existence of this dark state raised questions about how life ever could have begun, given that the genetic carriers were so easily mutated or destroyed during this very brief but very vulnerable time.
    “When the bases of DNA were first being formed billions of years ago [sic], the atmosphere was actually quite hostile,” Kong said.  “It was a period prior to any protective ozone layer on Earth and the ultraviolet radiation was very strong.  So if primordial DNA bases were forced into this vulnerable dark state, they should have incurred large amounts of photochemical damage that would have made the very survival of these bases difficult, let alone further evolution of life.”

At this point, the press release takes a dramatically optimistic turn: the dark state disappears in the presence of water.  “So if water were present, the earliest DNA bases would have been able to survive and eventually help form the basis for ever-more-complex life forms,” they claim. 

The findings suggest, Kong said, how water could have been an absolutely essential compound to allow early DNA bases to remain stable, resist mutation, and ultimately allow for the evolution of life….
“What this is really telling us is that life is a unified process,” Kong said.  “It’s not just a group of DNA bases, but it’s also the physical environment in which they exist.  Later on, as life became more evolved [sic], there were other ways to achieve genetic stability.  But at first, it simply may not have been possible without water.”

So while the news seems bad, they were able to spin it positively by adding water: “the presence of water was the key to the evolution of life on Earth, making it possible for life to emerge [sic] from what was once a hostile and unforgiving primordial soup of chemicals and radiation” [sic].  In other words, don’t try freeze-dried primordial soup.

The only good news here is that these researchers have not completely obliterated all hope.  This is not good news for the OOL (origin-of-life) school.  They have constrained further a hopeless situation (see online book).  This “radical heresy” removes any possibility of key building blocks forming away from water.  Remember when Steve Benner postulated ribose forming in a desert with boron, because it was too unstable in water? (11/05/2004)  Now, the poor guy has to make the ribose in the desert (hoping that UV radiation won’t destroy it there), then get it into the water where the A, C, T, G or uracil are, hoping somehow that they will join up with phosphates on some clay mineral, and then link into polynucleotide chains that can both code for information and perform enzymatic functions (RNA World), but also find a safe haven in some membrane that is not so tight it becomes a death trap.
    Sounds like a hard story to sell to Congress.  Things are not going too well for astrobiology these days.

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Categories: Genetics, Origin of Life

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