We’ve put man on the moon, visited Pluto and Jupiter, and even managed to land a probe on a speeding comet. But when it comes to the origins of life, it might come as a surprise to learn that science doesn’t have all the answers. “We have a really sketchy understanding of what early Earth looked like” says Dr Matthew Powner of UCL.
“There is no perfect geological record of how the earth looked 4 billion years ago, when the origin of life is expected to have taken place. The rocks get recycled through plate tectonics and the records get lost.” In the absence of a geological record, some of our best clues to understanding how life could have formed on planet Earth come from chemistry.
Because scientists have struggled to show how basic organic molecules could have formed together on Earth, some researchers have suggested the building blocks of life may have come from outside our solar system.
“Lots of people like to look at meteors that contain organic molecules. It’s kind of the coolest, right?” says Dr Powner. “But I’m not sold – I don’t need space-based delivery. The coolest and most exciting isn’t always the best in science. For me, the question is how you link up robust, earth-bound organic chemistry.” Dr Powner’s team is looking at doing exactly that – by demonstrating how chemical processes could have formed the basic building blocks for life on Earth billions of years ago.
Life on Earth is thought to have begun with RNA, the single-stranded cousin of our double helix DNA. Like DNA, RNA is made up of four essential building blocks. Two of these, uracil and cytosine, are built on a single ring of carbon and nitrogen atoms known as a pyrimidine. The other two, adenine and guanine, are built on a double ring of carbon and nitrogen atoms called a purine.
Until recently, scientists have been unable to show how both of these essential building blocks might have been formed from the same materials. As part of his PhD, Dr Powner succeeded in describing the first full route to producing pyrimidine molecules, but this is only half the story. “It’s been irritating for nearly 10 years that there is no complementary method for purine molecules.”
For the first time, Dr Powner’s group has managed to demonstrate in a paper published in Nature Communications, how both molecules might be formed from an 8-oxo-purine, a purine double ring containing an oxygen.
This is a huge step, but because of the 8-oxo group, the compound formed by Dr Powner’s group contains an oxygen where a hydrogen is normally located on RNA. “We’re one oxidation away from our ideal synthesis,” explains Dr Powner. “As we build the structure, this 8-oxo group lets us build in the selectivity, but it’s left over as a by-product.” While there are enzymes that can use this oxygen-containing RNA to function, it is still one away from describing RNA as we know it.
“Is that a problem? We’re not sure.” says Dr Powner, whose research group will continue to look both at how these oxygen-containing RNA function, and how to modify their synthesis to remove that oxygen. “I guess the thing that’s most important about this paper is that it’s not a one-off. It’s not something we’ve just started and we’re not going to stop now.”
Liz Killen is studying for an MSc in Science Communication