New Evidence for the RNA World

Every instructor of an introductory biology class is faced with a dilema to present to their class. While we know that DNA is the genetic material of all living organisms (except some viruses - but most do not consider them as "living"), it appears to have been absent from the early Earth. So what was the original genetic material? And, more importantly, do we have any evidence to support this hypothesis?

Before we look at the alternatives, was wasn't DNA the original genetic material on the planet? One main reason, of course, is its complexity, and the fact that DNA requires a host of proteins and enzymes to assemble and copy itself. These enzymes are encoded within the DNA, so that leaves us with a "chicken and egg" scenario. The DNA molecule itself lacks any catalytic abilities - meaning that it does not conduct any chemical reactions. It is like the hard-drive of your computer - pretty much useless without a host of assistants to get the information in and out.

For some time scientists have recognized that a second form of nucleic acid, RNA, is the solution to these problems. RNA is a much simpler molecule. It is usually short and only consists of a single-strand of nucleotides. More importantly, RNA molecules can themselves act an enzymes. This type of RNA is called a ribozyme, and its activity appears to solve many of hurdles faced by the early genetic material. The fact that RNA may have been the earliest form of genetic material is called the RNA world hypothesis.

There has been only been one real problem with the RNA world hypothesis. How did the individual components, called nucleotides, of the RNA molecule self-assemble. Many explanations have been proposed, but finally, due to the activities of a group of researchers at the University of Manchester, we are one step closer to understanding. Dr John Sutherland, a chemist has demonstrated a series of chemcial reactions that can occur naturally to form the nucleotides of RNA. This could be a very important advance in the life sciences - previously we have known how to form the nucleotides synthetically (i.e, in a lab), but not under natural conditions.

Now here is where we can link astrobiology (also called exobiology) and genetics together. We are currently exploring Mars for life, and will soon we taking a good look at both Europa and Titan (moons of Jupiter and Saturn, respectively). While it is useful to look for life as we know it - what would be more interesting would be to tart to look for proto-life, molecules that are self-assembling and replicating. Using Sutherland's data, we should be taking a good look at these locations of evidence of RNA-building blocks. By doing so we can understand more about how life first evolved on our planet.



For more on Sutherland's discoveries - see the NY Times article by Nicolas Wade - "Chemist Shows How RNA Can Be The Starting Point for Life"