Chemists cook up recipe for life
One of nature's enduring mysteries is how the complex systems that make up a functioning cell evolved in the first place. In particular scientists have struggled to explain the origins of DNA and its genetic relative RNA, both of which are used to store and carry genetic information in the form of a linked sequence of genetic letters or "bases", which each consist of three components, a sugar, an organic base and a phosphate group. And yet, despite significant effort, no one has ever found an easy way to make these complex molecules using the kinds of chemicals that would have been common on the early Earth - until now.
Writing in this week's Nature, Manchester chemist John Sutherland and his colleagues have uncovered an elegantly simple sequence of chemical steps that can create two of the four different letters used by the genetic code.
"We've worked out how to make C and U," says Sutherland. The team's synthesis starts with the chemicals cyanoacetylene, cyanamide, glycolaldehyde, glyceraldehyde and inorganic phosphate, all substances, as Sunderland points out "you see in space quite naturally and even in the smog surrounding Titan in our own solar system," indicating that they would probably have been present on a young planet Earth too. "Effectively we started with building blocks that were the equivalent of two halves of a sugar molecule and an organic base [the genetic letter], which we pieced together to make the whole" says Sunderland.
"This is where others went wrong in the past. They had tried to assemble genetic bases by looking for ways to link each of the intact individual components together, rather than by starting with bits of them." The reaction the team came up with generates large amounts of the genetic letter C, cytodine. This can be converted to uracil (U), a second genetic letter, with a blast of UV light, of which there would have been plenty because when life first evolved the Earth lacked an ozone layer.
Now the team are looking for a similarly simple way to make the other two bases. "Then we've got Darwin's little pond," says Sutherland. Regardless of whether they succeed or not, the present study shows that at least some of the components of genetic material can easily be synthesised from building blocks that would have been here when life began over 4 billion years ago.