How did life begin? It is a question that has been bothering the best minds of humanity since we first became self aware.
A pair of Scripps Research Institute scientists has taken a
significant step toward answering that question. The scientists have
synthesized for the first time RNA enzymes that can replicate
themselves without the help of any proteins or other cellular
components, and the process proceeds indefinitely.
While this does not sound like anything great to the average person, it is worth noting because RNA likely the predecessor of our current DNA, and figuring out how it replicated without the help of DNA has been a serious puzzle for many people in search of the origins of life.
the modern world, DNA carries the genetic sequence for advanced
organisms, while RNA is dependent on DNA for performing its roles such
as building proteins. It has been suspected that RNA once did the whole job by itself. A theory about lifes orginis, called the RNA World model, puts forth the idea that because RNA can
function as both a gene and an enzyme and that RNA might have come before DNA. This would make it the origin of modern life.
researchers have wondered whether there might be a simpler way to
copy RNA, then the current DNA dependant method. One that was dependant only on the RNA itself, but until now no
one could take the theory to reality.
Immortalizing Molecular Information
replicating system actually involves two enzymes, each composed of two
subunits and each functioning as a catalyst that assembles the other.
The replication process is cyclic, in that the first enzyme binds the
two subunits that comprise the second enzyme and joins them to make a
new copy of the second enzyme; while the second enzyme similarly binds
and joins the two subunits that comprise the first enzyme. In this way
the two enzymes assemble each other — what is termed cross-replication.
To make the process proceed indefinitely requires only a small starting
amount of the two enzymes and a steady supply of the subunits. "This is the only case outside biology where molecular information has been immortalized," sums up Joyce in a poetic manner.
The researchers then used this mode to generate a variety of enzyme
pairs with similar capabilities. With 12 pairs in all, and in true relaity TV generation fashion they pitted against each other them to compete in a molecular test of survival
of the fittest. Most times you ended up with the same replications, but every once and a while you woud get a mutation. It is these types of mutations that may have created the life we see around us now.
The research shows that the system can
sustain molecular information, a form of heritability, and give rise to
variations of itself in a way akin to Darwinian evolution. So, says
Lincoln, "What we have is non-living, but we've been able to show that
it has some life-like properties, and that was extremely interesting."