Here's a second theoretical option:
“The RNA world hypothesis is extremely unlikely,” said Charles
W. Carter Jr. “It would take forever.” Moreover, there’s no proof that such
ribozymes even existed billions of years ago. To buttress the RNA World
hypothesis, scientists use 21st century technology to create ribozymes that
serve as catalysts. “But most of those synthetic ribozymes,” Carter said, “bear
little resemblance to anything anyone has ever isolated from a living system… The
collaboration between RNA and peptides was likely necessary for the spontaneous
emergence of complexity,” Carter added. “In our view, it was a peptide-RNA
world, not an RNA-only world.”
Our genetic code is translated by two super-families of
modern-day enzymes. Carter’s research team created and superimposed digital
three-dimensional versions of the two super-families to see how their
structures aligned. Carter found that all the enzymes have virtually identical
cores that can be extracted to produce “molecular fossils” he calls Urzymes — Ur meaning earliest or
original. The other parts, he said, are variations that were introduced later,
as evolution unfolded. These two Urzymes are as close as scientists have gotten
to the actual ancient enzymes that would have populated the Earth billions of
years ago. “To think that these two Urzymes might have launched protein
synthesis before there was life on Earth is totally electrifying,” Carter said.
“I can’t imagine a much more exciting result to be working on, if one is
interested in the origin of life.” The study leaves open the question of
exactly how those primitive systems managed to replicate themselves — something
neither the RNA World hypothesis nor the Peptide-RNA World theory can yet
explain. Carter, though, is extending his research to include polymerases —
enzymes that actually assemble the RNA molecule. Finding an Urzyme that serves
that purpose would help answer that question.
Publication:
Li L, Francklyn C, Carter CW Jr., “Aminoacylating Urzymes Challenge the RNA
World Hypothesis,” 2013, The Journal of Biological Chemistry, 288, 26864; doi:10.1074/jbc.M113.496125
To visualize the problem, in your hydrothermal alkaline vents we should start off with something like this, perhaps in a more simplified form (something like the RNA of viruses, perhaps?):
According to Carter, the Ur-enzymes "launched protein synthesis before there was life on Earth." So, proteins were manufactured before cells saw the light of day. However, absolutely necessary for protein synthesis to succeed are the group II introns to edit and splice. Again we have the chicken or egg problem, for the cell or organism ribosome, with group II intron, to manufacture "just the right protein the organism requires at any given time." So, here a protein factory would have to start producing proteins before the factory has been built. This magical process has to spontaneously perpetuate and improve over the millenia until we end with something like this, the working of which is explained by the following article:
A major function of RNA is copying all genetic information
and making it readable by the cellular protein factories, the ribosomes. But
RNA needs to be edited, and an early step in the editing process is splicing. Splicing
consists of breaking apart the RNA and recombining its pieces in ways that
produce just the right protein the organism requires at any given time. In many
organisms this vital cut-and-paste action is sometimes self-catalyzed by
intrinsic RNA components called group II introns. In more complex organisms,
including humans, the process is performed by a similar yet more sophisticated
machinery, the spliceosome, which has evolved from and works like the group II
introns. “Splicing is a very basic phase of gene expression,” said Pyle, who is
also an investigator of the Howard Hughes Medical Institute. “Whenever splicing
gets messed up, you’ll find a disease that results. Until now we haven’t really
understood the splicing reaction chemically.” The researchers said RNA may
perform more functions than previously thought. “RNA is revealing its ability
to utilize metals in the environment to do its chemical transformations,” Pyle
said. “RNA can do complex chemistry, just like a protein can.”
The article is titled “Visualizing group II intron catalysis
through the stages of splicing.”
