Rising complexity and the ‘Big Birth’: A brave new RNA world

When looking into exploring rising complexity, I was immediately drawn to the origin of life. Organic life is like rising complexity on steroids – it is comprised of a complex arrangement of chemical materials and properties, the aggregate effect of which allows the emergent system to beget its own complexity. Through life’s tendency to proliferate genetic information, and the natural selection of the evolutionarily “fittest” of those genes, organic life is simply geared to become increasingly more complex over time – as long as it managed to pass a certain threshold level where the requisite conditions for its existence were met and sustained.

In this light, I was lucky enough to get into contact with Associate Professor Rowena Ball, a mathematical chemist and thermodynamicist at Australian National University, who leads an international research project addressing origin-of-life questions. Last year, her and co-researcher, Leeds University’s Professor John Brindley, hit the news when they published a breakthrough paper in the Journal of the Royal Society Interface suggesting that hydrogen peroxide – think: plastics and hair bleach – kick-started the chemical process which drove life. This year, another couple of studies from Ball’s research team have bolstered their theory. Not only do their findings provide a revelatory perspective about the existence of life within the universe, they have demonstrated how matter and energy was organised to cross that aforementioned threshold and form biological complexity.

“We actually know more about the origin of the universe than we know about the origin of life,” Ball started off saying. “We haven’t got any instrumentation that can probe it, so I don’t think we’ll ever be able to say, ‘this is how it happened,’ because we weren’t there to see it and nor do we have a Hubble Space Telescope to give us information [about it].” This was a sobering thought, but science tended to be no easy pushover. In order to get closer to understanding the origin of life, Ball said, researchers needed to “use scientific methodology to derive thermodynamically consistent hypotheses and test them in simulation and in the laboratory, and then we can even eventually produce artificial life in the laboratory”.

At this point, in my mind, it sounded like origin-of-life researchers were modern-day alchemists, transforming inert chemical matter into biological entities at their fingertips, all in the pursuit of discovering more about reality. However, for Ball, this wasn’t meant as a magic trick. Her aim was to provide a ‘eureka’ moment to cement the ‘RNA world hypothesis’ as an established scientific principle. “The RNA hypothesis is well-accepted, for many reasons,” she said. “There are a couple of smoking guns in modern biology that support it.” (See here for a more in-depth explanation.)

Champagne_vent_white_smokers

The RNA world hypothesis holds that communities of RNA grew in rock pores around hydrothermal vents and replicated and evolved

The RNA world hypothesis is, essentially, a very convenient solution to a very old problem: what came first, the chicken or the egg? Or, more specifically: what came first, genetic information (DNA) or a biocatalyst enzyme (protein)? As Richard Dawkins pointed out in his 2009 book The Greatest Show on Earth: “DNA can replicate, but it needs enzymes in order to catalyse the process. Proteins can catalyse DNA formation, but they need DNA to specify the correct sequence of amino acids”. There must have been an intermediate step leading up to the formation of DNA and protein, scientists presume.

There is, rather fortuitously, a candidate in the natural world which could fulfil this intermediary role: Ribonucleic acid (RNA). Not only does RNA join DNA and protein as one of the three types of macromolecules involved in the system of reproduction and metabolism used by all living cells – it is the ‘messenger’ that transfers genetic coding from DNA to protein, to let the latter know what its function is – it is also a convenient solution to the DNA/protein catch-22. Although it is much less complex than either DNA or protein, RNA is still a polynucleotide molecule, (just like DNA) while it can also act like an enzyme (just like proteins). It can therefore pass on genetic information and act as a biocatalyst for that activity, both at the same time. Based on this knowledge, and on what we know about the geological history of the earth, the RNA world hypothesis holds that communities of RNA grew in rock pores around hydrothermal vents and replicated and evolved, eventually passing on the mantle of genetic proliferation to the more complex entity, DNA.

“But there have been problems with it [the RNA world hypothesis] that have been regarded by its proponents as just problems that need to be worked on and that will be eventually solved, and by its opponents as fatal flaws,” Ball advised. For one thing, how could RNA replicate without cellular machinery powering the process? There needed to be some kind of external energy source, and one which fit within the criteria imposed by the rules of thermodynamics.  Such criteria necessitated the presence of a form of thermal cycling – a periodic energy source which produced a heating phase to separate the RNA’s base-paired double strands and a cooling phase to anneal both strands into a double helix.

According to Ball, a “thermochemical oscillator” in the primordial soup was needed to achieve this thermal cycling – and hydrogen peroxide presented as a viable candidate for it. My next post, Finding a lifeblood for life, looks into this in more detail.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s