This article was published in Scientific American’s former blog network and reflects the views of the author, not necessarily those of Scientific American
CHICAGO—There is a moment in Steven Spielberg's E.T.: The Extra-Terrestrial in which scientists realize that E.T. in fact has DNA, like Earth-based life forms. But that DNA is unlike any that scientists have thus far—it being 1982, of course—found in any Earthbound organism: It has six, instead of the usual four, bases in its alphabet.
Had E.T. been made today, a scientific consultant may have had to give a nod to a lab in Gainesville, Fla., where DNA with six nucleotides exists in a beaker.
"We have an artificial chemical system that is capable of Darwinian evolution," biochemist Steven A. Benner, of the Foundation for Applied Molecular Evolution in Gainesville, said at a session here at the American Association for the Advancement of Science's (AAAS) annual meeting this morning.
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But before you get too excited—or terrified—about mad scientists creating artificial life in the lab, Benner's caveats are worth noting: The system "is not self-sustaining."
In other words, this "artificial life" isn't alive at all, even if it works sort of like life does. And it's not going to rival E.T. anytime soon.
A quick review: DNA's four bases
—A for adenine, C for cytosine, G for guanine and T for thymine—pair off to store information that is translated into ribonucleic acid (RNA) and then into proteins. Benner told reporters yesterday that his team had created a system "made up of four molecules that are the basic building blocks of our DNA along with eight synthetic modifications of them," for a total of 12 bases, according to LiveScience.
Benner discussed those 12 bases—named Z, P, V, J, Iso-C, Iso-G, X and K—briefly this morning at a public session that we live-Twittered, but spent most of his time describing the six-base version of his team's "Artificially Expanded Genetic Information System." (That gave him a chance to bring up E.T.)
When the system copies itself, it can make mistakes, and some of those mistakes might be more likely to be copied than other sequences, which means natural selection and evolution. But the system needs a boost from something called the polymerase chain reaction, so it can't do the copying all on its own, like DNA can, and is therefore not self-sustaining. Benner said yesterday, however, that was just a few years away.
The point of all this? It's not to create a new version of life on Earth, although it's certainly at least a theoretical step in that direction. There are other such attempts, such as this one using a DNA-like molecule that has a triple, instead of double, helix. And there are related attempts to create artificial life in the lab using the same molecular biology in existing organisms.
What Benner and others are trying to do, with funding from NASA, is figure out what life might look like on other planets, if we ever find it. "One of the ways scientists try to understand life as a universal concept...is you try to make life on your own in the lab," Benner said yesterday, according to LiveScience. "We try to put together chemicals that do that."
That life on other planets may not be based on the same molecular biology that governs life on Earth, because of the composition of those planets and their atmospheres. So at today's session, other scientists described such "weird life" that could give clues to basis for extraterrestrial life. Paul Davies, a physicist, cosmologist, and astrobiologist at Arizona State University, described a "shadow biosphere" filled with the descendants of previous alien life on Earth.
As Davies and Benner pointed out, those descendants, and evidence of their ancestors, are most likely to be found at the microscopic level—Benner cited tiny structures in the Allan Hills meteorite as one potential example—not in the cute, if bizarre-looking, being from Steven Spielberg's imagination.
E.T., code home?
Image of DNA via Wikimedia
