Over at the blog Jesus Creed, RJS writes:
DNA is capable of passing information on from generation to generation – but it is not reactive and requires a complex series of reactions involving proteins for replication. Production of these proteins of require both RNA and additional proteins for transcription, and translation. The interrelated reactions are quite complex. DNA is a fairly stable (unreactive) molecule, making it good for information storage, but the chemistry of DNA is simply not rich enough for life to originate from DNA.
Proteins have a very rich chemistry and can perform many functions. But they are not capable of replication. There are no specific interactions that allow one amino acid chain to produce an identical chain.
Therefore – life did not originate with proteins, nor did it originate with DNA.
What RJS presents is the classic, foundational argument for the RNA world:
- DNA is inert, but it passes on information across time.
- Proteins don’t pass on information across time, but are reactive.
- RNA is both reactive and passes on information across time.
- Since life requires both reactivity and the ability to transmit information, life must have started with RNA.
But it’s not a simple as this.
First, DNA is not inert. Scientists have created a whole set of DNA enzymes known as DNAzymes. Here is a short excerpt from just one research article using these DNA-enzymes:
The 10–23 RNA cleaving DNAzyme is a catalytic nucleic acid composed entirely of DNA (Fig. (Fig.1)1Figure 1) (1). It was derived from a combinatorial library of sequences by in vitro selection. The tremendous activity and sequence specificity against its target RNA under simulated physiological conditions (2,3) has generated the expectation that it may function in cells as a gene suppression agent.
Yes, the reactivity is limited and man-made, but that is just an observation of our current understanding. The point that matters is that DNA is not inert.
I would also add that proteins can pass on information – simply consider prions and evolution:
In reality, all three biomolecules (RNA, DNA, and proteins) are reactive and transmit information. One can make arguments about differing degrees, that are a function of our current understanding, but the forceful beauty and simplicity of the original argument for the RNA world is gone.
Look, I don’t deny the existence of the RNA world. But I would remind people that the RNA world is neither a fact nor a well supported theory – it is a hypothesis/speculation that amounts to a vague “looks like” argument supported by strands of circumstantial evidence with a mixed bag of predictive success. That’s it. While I cannot deny the RNA world once existed (it sounds plausible and would fit well within a teleological explanation), neither can I cheerlead for the RNA world because of some serious, fundamental concerns.