The RNA world
There's a lot of evidence that the current genetic material,
DNA, was preceded - not by clay minerals - but by RNA.
The "RNA world" hypothesis suggests that the roles of
proteins and enzymes were once played by curled-up RNA
This hypothesis has a great deal of experimental support.
In particular there are still RNA enzymes (Ribozymes) in use
in modern organisms.
Indeed the functional part of the ribosome, (which
translates RNA into proteins), is basically a ribozyme.
It doesn't take much imagination to guess that there might
once have been more of these things.
However, the "RNA world" is not itself hypothesis a
about the actual origin of life - since RNA is not
remotely plausible in the role of the first genetic
Unfortuately there is a lot of garbage about the
RNA world in circulation on the internet, that is liable to
confuse and mislead people.
RNA world hypothesis, for example, suggests that short RNA molecules
could have spontaneously formed that would then catalyze their own
The RNA World hypothesis holds that in the primordial soup
(more likely the primordial sandwich), there were RNA and
DNA base pairs floating around. Since it is of lower energy
for base pairs to form a chain, this would happen with some
regularity. However, these chains are not of much lower
energy than free base pairs, so the chains would also break
apart with some regularity. However, some sequences of base
pairs have catalytic properties - catalytic properties which
lowers the energy of that same chain being created. As more
and more of these RNA chains are created, they catalyze the
formation of yet more. This causes chains to form faster
than they break down, creating a positive feedback loop.
These chains are proposed to be the first, primitive forms
There is a lot of material out there along similar
Nonsense like this makes the RNA world hypothesis appear
ridiculous. The problems in the proposed scenario are
stupendous. For one thing, nucleotide isomeric impurity
blocks replication of RNA. For another, there is no
plausible way that primed nucleotides could be supplied.
AFAIK, nobody seriously interested in the origin of
life believes this silly hypothesis.
Perhaps proponents of the RNA world should take more care to
emphasise that the notion that the RNA world was primitive
is not biologically plausible - rather than
associating themselves with the idea.
The RNA world was obviously constructed by more
primitive agents - (of which there are no shortage of
candidates) - rather than forming out of nothing.
The RNA world itself is a fine hypothesis. However, I wish
that people would stop muddling it together with a lot of
garbage about the RNA world being first.
- The origin of life - a review of facts and speculations
- Prebiotic synthesis of nucleotides
- Constructing an RNA world
- RNA-catalysed nucleotide synthesis
- Synthesis of RNA oligomers on heterogeneous templates
- Surprising fidelity of template-directed chemical ligation of oligonucleotides
- Prebiotic ribose synthesis: a critical analysis
- The improbability of prebiotic nucleic acid synthesis
- The prebiotic role of adenine: a critical analysis
- Prebiotic cytosine synthesis: a critical analysis and implications for the origin of life
Tim Tyler |