A relatively simple combination of naturally occurring sugars and amino acids formed on Earth before any life existed offers a plausible route to RNA, researchers at the University of California, Merced, have found.

Biological molecules, such as RNA and proteins, can exist as enantiomers. Enantiomers are two molecules that are identical except for the three dimensional arrangement of the atoms that make it up. One of the best examples is your left and right hands — they are the same except they are mirror images of each other.

In biological systems, only one “hand” or enantiomer of the basic molecules that make up DNA, RNA, proteins, and sugars is used. This is a key aspect to how biological systems work: when the molecules interact, only ones with the correct three-dimensional shape will work together — just as the proper way to shake someone’s right hand is to use your right hand and not your left.

The researchers found that having only one enantiomer available is a very important aspect of the origin of life. The problem of creating RNA breaks down into two parts: (1) making up the complex molecules like RNA and proteins needed for life to work, and (2) making sure those molecules were made up of the right enantiomers.

By studying the chemical reactions carefully, the research team found that it was possible to provide the natural (found in nature) enantiomer of precursor molecules that would evolve into RNA. The natural enantiomer of the RNA precursor molecules formed a crystal structure visible to the naked eye. The crystals were stable and avoided normal chemical breakdown. And they can exist until the conditions are right for them to change into RNA.

The scientists said their research fills a major gap in the knowledge of molecular evolution. Researchers had previously shown that very simple chemicals can spontaneously make simple building blocks of more complex biological molecules.

In a separate field of research, other scientists have demonstrated that once they have one enantiomer of RNA, they can start making simple self-replicating systems.

“The key question was how do you get from those basic building blocks to RNA. This what we really answered, linking the two fields of research,” said Jason Hein, Ph.D.

Ref.: Jason E. Hein, Eric Tse, and Donna G. Blackmond, A route to enantiopure RNA precursors from nearly racemic starting materials, Nature Chemistry, 2011; [DOI: 10.1038/NCHEM.1108]