The RNA World hypothesis just got a big boost
The RNA World hypothesis just got a big boost.
This article at the NY Times is reporting that two of the four building blocks of RNA have been synthesized more or less “from scratch” in a “primordial soup” similar to what was thought to exist on earth before life began by a team of scientists led by organic chemist John Sutherland.
This problem has been a real brain-breaker over the last 20 years. Getting “half way there” was seemingly understood. There was a plausible mechanism for getting the three components of an RNA nucleotide: a base, a sugar, and a phosphate group. But figuring out how these three could be combined to form an RNA nucleotide proved to be elusive. Turns out there’s another route. Instead of constructing these three parts of the nucleotide and then attempting to combine them:
They make a half-sugar/half-base (11), add another half-sugar (12) and then a half-base to make an intermediate (13) that easily becomes ribo-cytidine phosphate.
Ultra-violet light converts ribocytidine to the uracil-containing nucleotide.
Two down, two to go.
This hypothesis is not without dissent, and I don’t mean the typical creationist variaty of dissent.
However, Robert Shapiro, professor emeritus of chemistry at New York University disagrees. ‘Although as an exercise in chemistry this represents some very elegant work, this has nothing to do with the origin of life on earth whatsoever,’ he says. According to Shapiro, it is hard to imagine RNA forming in a prebiotic world along the lines of Sutherland’s synthesis.
‘The chances that blind, undirected, inanimate chemistry would go out of its way in multiple steps and use of reagents in just the right sequence to form RNA is highly unlikely,’ argues Shapiro. Instead, he advocates the metabolism-first argument: that early self-sustaining autocatalytic chemosynthetic systems associated with amino acids predated RNA.
Carl Zimmer does a great job of explaining it on his blog, “The Loom” The comments and bibliography there are worth checking out as well.
I probably should have linked to Carl Zimmer’s entry first, rather than to the NY times, as Carl seems to have been onto this story before the research was even completed.
Via Carl Zimmer’s blog, here is the link to the abstract, Synthesis of activated pyrimidine ribonucleotides in prebiotically plausible conditions, in Nature.
Note: I myself know Jack Squat about organic chemistry, so don’t take my word for it.