What are chemical candidates for replicator molecule?

Question

I have read `Selfish gene` by Richard Dawkins and idea is that at random some molecule was synthesized that had a property if there is enough 'materials' to construct copy of itself - it would. And then it made bunch of it's copies and then copies started mutating and eventually we got to DNA in us.In his book he never says what actual molecule is original replicator. **What are chemical candidates for original replicator molecule?**

Answer 1

The self-progenitor molecule would have to be an enzyme capable of replicating the genetic code of the earliest organisms. Enzymes are proteins capable of increasing the rate of a chemical reaction to a speed necessary for life to exist. The genetic code describes a biomolecule capable of encoding proteins (you could think of it as an instruction book on how a cell should make proteins); the genetic code of life on Earth is DNA.

The vastly simplified process by which DNA encodes for proteins is this: DNA is converted into RNA, a very similar biomolecule, which encodes for the amino acids that make up proteins. The RNA made from DNA is used to determine amino acid (protein building block) sequence (order) and therefore make functional proteins and enzymes.

The very first organisms (or, there biochemical progenitor's) are believed to have had an RNA, rather than DNA, genetic code. RNA, though not itself a protein, can fold itself into structures resembling the macrostructure of proteins and can therefore catalyze reactions just like an enzyme could, but without any enzymes needed. A multitude of examples in which organism's have RNA molecules that catalyze reactions have been discovered since originally seen in 1982. And in fact, recently, scientists at Oxford have succeeded in synthesizing an RNA molecule capable of replicating itself.

So, we established that RNA can:

a) act as the genetic code for amino acid sequences, therefore theoretically can be a genetic code for an organism without DNA

b) catalyze reactions in some cases, therefore theoretically able to replicate itself

c) Can in fact replicate itself in lab

Therefore, I think it's reasonable to say that some form of RNA molecule was the original self-replicator. The exact sequence/origin of this molecule, however, is unknown.