SAN DIEGO: Can life arise from nothing but a chaotic assortment of basic molecules? The answer is a lot closer following a series of ingenious experiments that have shown evolution at work in non-living molecules.
For the first time, scientists have synthesized RNA enzymes – ribonucleic acid enzymes also known as ribozymes – that can replicate themselves without the help of any proteins or other cellular components.
What’s more, these simple nucleic acids can act as catalysts and continue the process indefinitely.
“There’s nothing in biology in this system: no proteins, no cells, no biological matter. We just provide them with the building blocks,” said molecular biologist Gerald Joyce of the Scripps Research Institute in San Diego.
“They’re just molecules, so they do what they do until they run out of substrate. And this will go for ever – it’s an immortal molecule, if you like,” he told a meeting of the American Association for the Advancement of Science in San Diego.
Since he and colleague Tracey Lincoln first succeeded in creating this artificial genetic system that can undergo self-sustained replication and evolution last year, the molecules have changed dramatically as they evolve better and better solutions.
Survival of the fittest
The researchers began with ribozymes known to occur naturally, and put these in a growth medium, heated them and allowed the ribozymes to replicate until they had exhausted their fuel – usually within an hour.
The team then extracted a random subset, and put them in a new medium: ribozymes then competed with each other to consume as much of the medium as possible.
Eventually more successful ribozymes came to dominate the culture, and as the process continued, the ribozymes – undergoing evolution – grew in complexity, blindly finding solutions that made them more successful.
“The key thing is it replicates itself, and passes information from parent to progeny down the line,” Joyce told Cosmos Online.
“There’s roughly 30 bits of information passed. Some functions are more fit than others, and those that are more fit ‘breed’ more, and are perpetuated more efficiently, and so it goes Darwinian.”
The ultimate goal is to create genetic systems that behave like life, and are for all intents ‘life’ as we know it, but arose without using biological systems.
“The aim is to create systems that have inventive capabilities, that can develop novel solutions to challenges posed by the environment. But that we don’t have yet,” he said.
“What we do have is a self-sustained chemical system that undergoes Darwinian evolution.
Synthetic genetic systems
“They are synthetic genetic systems, and they are evolving. But they’re not living because they don’t yet show the capacity to invent functions out of whole cloth [independently from basic building blocks].
“The idea is to given them enough information wherewithal [build up enough genetic informaton] so they can start inventing their own solutions, rather than just optimising existing solutions,” he added.
Joyce said it was not practical to synthesize the more complex DNA-based life we know from scratch; it’s too complex and probably beyond today’s science. But it is conceivable to start with a much more basic form of life-like molecules based on RNA, and use evolution to build on them.
RNA world hypothesis
Many scientists believe that early life was based on RNA and predated the arrival of life based on deoxyribonucleic acid (DNA) and proteins. RNA, which can both store information like DNA as well as act as an enzyme like proteins, and may have supported pre-cellular life.
A lading proponent of the so-called ‘RNA world’ hypothesis, Joyce believes that RNA-based catalysis and information storage may have been the first step in the evolution of cellular life.