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DNA could have existed long before life itself
Snorri Gunnarsson/flickr/getty
THIS WEEK
In the beginning Earth created DNA Michael Marshall
THE latest twist in the origin-oflife tale is double helical. Chemists are close to demonstrating that the building blocks of DNA can form spontaneously from chemicals thought to be present on the primordial Earth. If they succeed, their work would suggest that DNA could have predated the birth of life. DNA is essential to almost all life on Earth, yet most biologists think that life began with RNA. Just like DNA, it stores genetic information. What’s more, RNA can fold into complex shapes that can clamp onto other molecules and speed up chemical reactions, just like a protein, and it is structurally simpler than DNA, so might be easier to make. After decades of trying, in 2009 researchers finally managed to generate RNA using chemicals that probably existed on the early Earth. Matthew Powner, now at University College London, and 12 | NewScientist | 25 August 2012
his colleagues synthesised two of the four nucleotides that make up RNA. Their achievement suggested that RNA may have formed spontaneously – powerful support for the idea that life began in an “RNA world”. Powner’s latest work suggests that a rethink might be in order. He is trying to make DNA nucleotides through similar methods to those he used to make RNA nucleotides in 2009. And he’s getting closer. Nucleotides consist of a sugar attached to a phosphate and a nitrogen-containing base molecule – these bases are the familiar letters of the genetic code. DNA nucleotides, which link together to form DNA, are harder to make than RNA nucleotides, because DNA uses a different sugar that is tougher to work with. Starting with a mix of chemicals, many of them thought to have been present on the early Earth, Powner has now created a sugar like that in DNA, linked to a
switched to DNA because DNA is better at storing information. In other words, RNA organisms made the first DNA. If that is true, how did life make the switch? Modern organisms can convert RNA nucleotides into DNA nucleotides, but only using special enzymes that are costly to produce in terms of energy and materials. “You have to know that DNA does something good for you before you invent something like that,” Switzer says. He says the story makes more sense if DNA nucleotides were naturally present in the environment. Organisms could have taken up and used them, later developing the tools to make their own DNA once it became –Lurking at the dawn of life– clear how advantageous the molecule was – and once natural molecule called AICA, which is supplies began to run low. similar to a base (Journal of the Early organisms must have American Chemical Society, doi. scavenged for materials in this org/h6q). way, says Matthew Levy of the There is plenty still to do. Albert Einstein College of Powner needs to turn AICA into a Medicine in New York City. “The base, and add the phosphate. His early Earth was probably a bloody molecule also has an unwanted mess,” he says, with all manner sulphur atom, which helped the of rich pickings on offer. reactions along but now must be Powner suggests another removed. Nevertheless, a DNA alternative. Life may have begun nucleotide is just a few years away, with an “RNA and DNA world”, says Christopher Switzer of the in which the two types of University of California, Riverside. nucleotides were intermingled. “It’s practically a fait accompli at Powner’s co-author Jack Szostak, this point.” of the Harvard Medical School, That could have important has shown that “mongrel” implications for our molecules containing a mix of DNA and RNA nucleotides can “Organisms could have used perform some of the functions of naturally occurring DNA, pure RNA (Proceedings of the then developed the tools National Academy of Sciences, doi. to make their own” org/bj8r97). Powner suggests that life started out using these hybrid understanding of life’s origins. molecules, gradually purifying Prebiotic chemists have so far them into DNA and RNA. largely ignored DNA, because its Benner says it makes more complexity suggests it cannot sense for the first life to have used possibly form spontaneously. pure DNA and RNA as early as “Everybody and his brother has possible. Both work better than been saying ‘RNA, RNA, RNA’,” the mongrel molecules. says Steven Benner of the Right now, though, there’s Foundation for Applied Molecular nothing to tell us exactly how and Evolution in Gainesville, Florida. when life first used DNA. “It almost Conventional wisdom is that becomes a choose-your-ownRNA-based life eventually adventure game,” says Levy. n
THIS WEEK
In the beginning Earth created DNA Michael Marshall
THE latest twist in the origin-oflife tale is double helical. Chemists are close to demonstrating that the building blocks of DNA can form spontaneously from chemicals thought to be present on the primordial Earth. If they succeed, their work would suggest that DNA could have predated the birth of life. DNA is essential to almost all life on Earth, yet most biologists think that life began with RNA. Just like DNA, it stores genetic information. What’s more, RNA can fold into complex shapes that can clamp onto other molecules and speed up chemical reactions, just like a protein, and it is structurally simpler than DNA, so might be easier to make. After decades of trying, in 2009 researchers finally managed to generate RNA using chemicals that probably existed on the early Earth. Matthew Powner, now at University College London, and 12 | NewScientist | 25 August 2012
his colleagues synthesised two of the four nucleotides that make up RNA. Their achievement suggested that RNA may have formed spontaneously – powerful support for the idea that life began in an “RNA world”. Powner’s latest work suggests that a rethink might be in order. He is trying to make DNA nucleotides through similar methods to those he used to make RNA nucleotides in 2009. And he’s getting closer. Nucleotides consist of a sugar attached to a phosphate and a nitrogen-containing base molecule – these bases are the familiar letters of the genetic code. DNA nucleotides, which link together to form DNA, are harder to make than RNA nucleotides, because DNA uses a different sugar that is tougher to work with. Starting with a mix of chemicals, many of them thought to have been present on the early Earth, Powner has now created a sugar like that in DNA, linked to a
switched to DNA because DNA is better at storing information. In other words, RNA organisms made the first DNA. If that is true, how did life make the switch? Modern organisms can convert RNA nucleotides into DNA nucleotides, but only using special enzymes that are costly to produce in terms of energy and materials. “You have to know that DNA does something good for you before you invent something like that,” Switzer says. He says the story makes more sense if DNA nucleotides were naturally present in the environment. Organisms could have taken up and used them, later developing the tools to make their own DNA once it became –Lurking at the dawn of life– clear how advantageous the molecule was – and once natural molecule called AICA, which is supplies began to run low. similar to a base (Journal of the Early organisms must have American Chemical Society, doi. scavenged for materials in this org/h6q). way, says Matthew Levy of the There is plenty still to do. Albert Einstein College of Powner needs to turn AICA into a Medicine in New York City. “The base, and add the phosphate. His early Earth was probably a bloody molecule also has an unwanted mess,” he says, with all manner sulphur atom, which helped the of rich pickings on offer. reactions along but now must be Powner suggests another removed. Nevertheless, a DNA alternative. Life may have begun nucleotide is just a few years away, with an “RNA and DNA world”, says Christopher Switzer of the in which the two types of University of California, Riverside. nucleotides were intermingled. “It’s practically a fait accompli at Powner’s co-author Jack Szostak, this point.” of the Harvard Medical School, That could have important has shown that “mongrel” implications for our molecules containing a mix of DNA and RNA nucleotides can “Organisms could have used perform some of the functions of naturally occurring DNA, pure RNA (Proceedings of the then developed the tools National Academy of Sciences, doi. to make their own” org/bj8r97). Powner suggests that life started out using these hybrid understanding of life’s origins. molecules, gradually purifying Prebiotic chemists have so far them into DNA and RNA. largely ignored DNA, because its Benner says it makes more complexity suggests it cannot sense for the first life to have used possibly form spontaneously. pure DNA and RNA as early as “Everybody and his brother has possible. Both work better than been saying ‘RNA, RNA, RNA’,” the mongrel molecules. says Steven Benner of the Right now, though, there’s Foundation for Applied Molecular nothing to tell us exactly how and Evolution in Gainesville, Florida. when life first used DNA. “It almost Conventional wisdom is that becomes a choose-your-ownRNA-based life eventually adventure game,” says Levy. n