DNA is the software of life and contains all the genetic information of a cell. The information in DNA is stored as a code made up of four chemical bases: adenine (A), guanine (G), cytosine (C), and thymine (T). Human DNA consists of about 3 billion bases, and more than 99 percent of those bases are the same in all people. The order, or sequence, of these bases determines the information available for building and maintaining an organism, similar to the way in which letters of the alphabet appear in a certain order to form words and sentences. An important property of DNA is that it can replicate, or make copies of itself. Each strand of DNA in the double helix can serve as a pattern for duplicating the sequence of bases. This is critical when cells divide because each new cell needs to have an exact copy of the DNA present in the old cell. DNA and the genes within it are where mutations occur, enabling changes that create new species.
RNA is the close cousin to DNA and in fact, is thought to be a primitive ancestor of DNA. RNA can't run a life form on its own, but 4 billion years ago it might have been on the verge of creating life, just needing a basic chemical fix to make the leap. It differs from DNA in a few ways. For instance, while DNA is double stranded, RNA is single stranded. It’s primary function is protein synthesis within the cell but it is also involved in the transmission of DNA information.
The Scripps Research Institute researchers synthesized RNA enzymes that can replicate themselves without the help of any proteins or other cellular components, and the process proceeds indefinitely. "Immortalized" RNA, they call it, at least within the limited conditions of a laboratory. More significantly, the scientists then mixed different RNA enzymes that had replicated, along with some of the raw material they were working with, and then sat back and watched them compete against each other. Remarkably, they then bred. The researchers also noted that now and then, one of these RNA would screw up, binding with some other bit of raw material it hadn't been using. Exactly what true life forms do. These new “species” would then replicate growing in number to dominate the mixture.
"It kind of blew me away," said team member Tracey Lincoln of the Scripps Research Institute, who is working on her Ph.D. "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."
Lincoln's advisor, professor Gerald Joyce, reiterated that while the self-replicating RNA enzyme systems share certain characteristics of life, they are not life as we know it. "What we've found could be relevant to how life begins, at that key moment when Darwinian evolution starts," Joyce said in a statement.
Some scientists familiar with the work have argued that this is life. Another scientist said that what the researchers did is equivalent to recreating a scenario that might have led to the origin of life. Joyce insists he and Lincoln have not created life: "We're knocking on that door," he says, "but of course we haven't achieved that."
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