Molecules assemble in water, hint at origins of life

[Jim__]

(Phys.org)—The base pairs that hold together two pieces of RNA, the older cousin of DNA, are some of the most important molecular interactions in living cells. Many scientists believe that these base pairs were part of life from the very beginning and that RNA was one of the first polymers of life. But there is a problem. The RNA bases don't form base pairs in water unless they are connected to a polymer backbone, a trait that has baffled origin-of-life scientists for decades. If the bases don't pair before they are part of polymers, how would the bases have been selected out from the many molecules in the "prebiotic soup" so that RNA polymers could be formed?

Researchers at the Georgia Institute of Technology are exploring an alternate theory for the origin of RNA: they think the RNA bases may have evolved from a pair of molecules distinct from the bases we have today. This theory looks increasingly attractive, as the Georgia Tech group was able to achieve efficient, highly ordered self-assembly in water with small molecules that are similar to the bases of RNA. These "proto-RNA bases" spontaneously assemble into gene-length linear stacks, suggesting that the genes of life could have gotten started from these or similar molecules. The research is published online in the Journal of the American Chemical Society.

The discovery was made by a team of scientists led by Georgia Tech Professor Nicholas Hud, who has been trying for years to find simple molecules that will assemble in water and be capable of forming RNA or its ancestor. Hud's group knew that they were on to something when they added a small chemical tail to a proto-RNA base and saw it spontaneously form linear assemblies with another proto-RNA base. In some cases, the results produced 18,000 nicely ordered, stacked molecules in one long structure.

"Thinking about the origin of RNA reminds me of the paradox of your grandfather's ax," said Hud, a professor in the School of Chemistry and Biochemistry. "If your father changed the handle and you changed the head, is it the same ax? We see RNA the same way. Its chemical structure might have changed over time, but it was in continual use so we can consider it to be the same molecule."

more ...

[longship]

1. Ken Ham's response...

Oh yeah??

R&K

[DreamGypsy]

2. Cool. Here's the abstract ....

from the ACS Journal:

Molecular self-assembly is widely appreciated to result from a delicate balance between several noncovalent interactions and solvation effects. However, current design approaches for achieving self-assembly in water with small, synthetic molecules do not consider all aspects of the hydrophobic effect, in particular the requirement of surface areas greater than 1 nm2 for an appreciable free energy of hydration. With the concept of a minimum hydrophobic surface area in mind, we designed a system that achieves highly cooperative self-assembly in water. Two weakly interacting low-molecular-weight monomers (cyanuric acid and a modified triaminopyrimidine) are shown to form extremely long supramolecular polymer assemblies that retain water solubility. The complete absence of intermediate assemblies means that the observed equilibrium is between free monomers and supramolecular assemblies. These observations are in excellent agreement with literature values for the free energy of nucleic acid base interactions as well as the calculated free energy penalty for the exposure of hydrophobic structures in water. The results of our study have implications for the design of new self-assembling structures and hydrogel-forming molecules and may provide insights into the origin of the first RNA-like polymers.

So the particular example is somewhat artificial, but developing mechanisms like this for replication is crucial for exploring the chemical origins of life.

Here's the graphic from the abstract:



Thanks for the post J__.