Saturday, January 13, 2007

Making life's first RNA molecules

Scientists have discovered a way to synthesize an important component of RNA from small molecules. The finding lends support to the RNA world hypothesis, which is one of the hypotheses describing how life got started on earth.

RNA is the intermediary between DNA and protein. DNA gives cells instructions, proteins carry out the instructions. But somehow, this all had to get started from extremely simple molecules, like ammonia, water, methane and carbon dioxide.

DNA is a difficult molecule to make. Its sugar portion has a modification that can only happen with enzymes. It is incredibly unlikely to find it naturally. That's where the RNA world hypothesis comes in: it has a much easier to make sugar, therefore it was the molecule that started life on Earth, not DNA, even though DNA is now by far the most common genetic material. Only a few viruses use RNA to transmit information through generations.

Importantly, strands of RNA can catalyze reactions. Scientists think this could have led to the formation of proteins and DNA.

The details are not completely known. But John Sutherland and colleagues from the University of Manchester have found a way to make the sugar portion of RNA from three smaller precursor molecules, glyceraldehyde-3-phosphate, 2-aminooxazole, cyanoacetylene, and water.

Water was common on the primordial earth. The scientists speculate that the other two molecules could combine when one evaporates and is delivered to the location of the second component in rainfall.

By doing this, they sidestep a chemical bottleneck that avoids creating a problematic molecule, ribose-phosphate, which is hard to make and decays quickly, and they also offer a way of making RNA from smaller molecules, which may show how life got started from small molecules.

It should also stick in the craw of creationists and intelligent design fans. They always like to wonder how complex things arose, an argument that basically stems from personal incredulity. Well, if this discovery pans out, it shows just such a logical way.

Reference:

J. Am. Chem. Soc., 129 (1), 24 -25, 2007. 10.1021/ja066495v S0002-7863(06)06495-X
Web Release Date: December 13, 2006 Copyright © 2006 American Chemical Society
Two-Step Potentially Prebiotic Synthesis of -D-Cytidine-5'-phosphate from D-Glyceraldehyde-3-phosphate
Carole Anastasi, Michael A. Crowe, and John D. Sutherland