Tuesday, May 19, 2009

RNA Excitement

A new study of the nucleotides that make up RNA may be the biggest science story of the decade, maybe the century.  It has been known since the 1950's that amino acids, the building blocks of proteins, could be synthesized from existing chemicals on the young earth.  We have also discovered that many of these amino acids, and other more complex organic molecules, have arrived from space in comets and metiorites.  We know the ingredients were laying around.  But there has been little progress in showing how the ingredients were assembled.  This question has sparked a thousand theories.  But until now, none had succeeded in creating a credible model of how you progress from the building blocks to the edifice.  One of the more popular theories is that self-replication started with RNA and that DNA was a later advance.  There are some RNA based life forms (the term is used loosely) such as retro-viruses like HIV.  The advantage of this theory is that RNA is easier to make from the building blocks than DNA.

Even so, every attempt to synthesize the nucleotides that make up RNA has failed.  But that just changed.  This article in the NYT discusses the discovery of a method that results in nucleotides self-assembling.  Its an article well worth reading.  But here is the key paragraph:
He (chemist John Sutherland) has solved a problem that for 20 years has thwarted researchers trying to understand the origin of life — how the building blocks of RNA, called nucleotides, could have spontaneously assembled themselves in the conditions of the primitive earth. The discovery, if correct, should set researchers on the right track to solving many other mysteries about the origin of life. It will also mean that for the first time a plausible explanation exists for how an information-carrying biological molecule could have emerged through natural processes from chemicals on the primitive earth.

Wow.  That's a big discovery.  If you read the details in the article, it becomes quite convincing.  I obviously can't evaluate the chemistry, but his theory resonates intuitively.  He describes a process of fits and starts, random and messy, just as we observe in the living world.  More importantly, his theory posits that life was a process, not an event.  It could have started a million times, and come to fruition once, or ten thousand times.  It may have happened several times over multiple eras.  But the key thing is that there is no point where you can say "there, that's life!"  You can say that at the beginning there's no life, and at the end there is.  There is the possibility of many intermediate steps, none of which constitute a magic moment.

As we are beginning to learn through the study of viruses, bacteria and archea, defining what is and is not alive isn't exact.  There is no acid test.  By some definitions, a virus is not alive, but a mule is.  By other definitions, a virus is alive, but a mule is not.  Obviously, this is a problem of imagination.  But Sutherland's theory accomidates everything that self-replicates.

This theory also fits with observations that there was probably no single organism that is the ancestor of all life on earth.  It would appear from the DNA that certain problems were solved more than once and that several alternative designs are present on earth.  There is the possibility that life actually formed multiple times, and that similar problems were solved in similar ways by otherwise unrelated organisms.  If the formation of life on earth was not a single, unique event, then it becomes more likely it happened elsewhere.  Lots of implications.

There are lots of people chasing this subject.  However, they couldn't get much beyond go until someone came up with a credible scenario.  That's now happened.  Look for a lot of quick progress on multiple fronts as a result.