Sunday, 30 March 2014

Hydrogen Peroxide, RNA And The Origin Of Life

Black smokers could have provided the environment
where the RNA World first formed.
In the mid 20th century Francis Crick and Leslie Orgel proposed a revolutionary solution to the origin of life: The RNA World Hypothesis. In this remarkable model of the origin of life information, energy and molecules were exchanged as a set of chemical systems similar to those found in cells, capable of perpetuating the existence of genes and their products; but all based around RNA. RNA is chemically simpler compared to DNA and would have had a greater chance of forming in a prebiotic environment. In time RNA would gave given way to the DNA-based system used by cells today.

Now an intriguing study has revealed a potential energy source for the RNA World. All chemical systems require energy to work, but the RNA world in particular needs a very specific temperature cycle; heating to 40 - 50 degrees Celsius to separate the base-paired strands of RNA and a cooling phase of 10 to 20 degrees Celsius to anneal complementary strands into newly replicated helixes.

This is difficult to achieve. A team of researchers led by Dr Rowena Ball from the Australian National University, however, have found that a reaction of hydrogen peroxide provides the exact cycle of temperature changes needed to drive RNA replication. Hydrogen peroxide decomposes into water and oxygen, releasing heat in the process, a natural thermo-chemical oscillator. What is interesting is that hydrogen peroxide's decomposition period, 90 seconds, is exactly the time needed to drive RNA replication.

RNA under a microscope.
By using a mathematical model consisting of hydrogen peroxide, RNA and the molecules needed for replication of genetic information, Dr Ball and her researchers showed that RNA concentration doubled every 0.3 seconds.

What is more, previous experiments have shown that RNA strands can undergo evolution and adaptation, losing ineffectual nucleotides to keep only the essentials to speed up their replication. Hydrogen peroxide could act as a mutagen, helping introduce diversity into the RNA pool and increase the pace of evolution.

'Ideally I'd like to set up a long-term experiment that can be just left to go for years and years,' said Dr Ball. 'Because evolution and natural selection will be happening, every year or two you could sample and see what you ended up with.' While hydrogen peroxide is not present in great quantities today, in the environment of the early Earth it would have been far more common. Yet the origin of cells is somewhat murky. In time we will have an increasingly clearer picture of how a world based around DNA came into existence.