Skeptophilia (skep-to-fil-i-a) (n.) - the love of logical thought, skepticism, and thinking critically. Being an exploration of the applications of skeptical thinking to the world at large, with periodic excursions into linguistics, music, politics, cryptozoology, and why people keep seeing the face of Jesus on grilled cheese sandwiches.

Wednesday, June 8, 2022

The glass RNA factory

A couple of months ago, I wrote about a discovery that has startling (and encouraging) implications for the search for extraterrestrial life -- that amino acids, the building blocks of proteins, are so easy to form abiotically that they are common even in interstellar dust clouds.

Well, because of my twin-brudda-from-anudda-mudda, the wonderful writer and blogger Andrew Butters, I found out that a new bit of research has shown that another piece of biochemistry -- RNA -- is equally easy to make in large quantities.

If anything, this is even more exciting to us aliens-in-space aficionados than the amino acid research was, because the model for the origins of life on Earth that is now virtually universally accepted is called "RNA world."  The idea has been around since the early 1960s, and simply put, it's that the first nucleic acid type to form in the early oceans was not DNA, but RNA.  At first this model met with considerable skepticism.  One common criticism was that the only organisms that encode their genome as RNA are certain viruses (such as the common cold, flu, rabies, mumps, measles, hepatitis, and COVID-19); all other organisms encode their genomes as DNA.  The second is that RNA has a tendency to be unstable.  It's a single helix; the shape resembles a spiral with short spokes sticking out at angles along its length, and that open shape allows it to be attacked and broken down readily by solvents (including water).

[Image licensed under the Creative Commons DataBase Center for Life Science (DBCLS), 201904 RNA, CC BY 4.0]

Two subsequent discoveries tilted biochemists toward accepting the RNA world model.  First, it was found that there are stable forms of RNA, such as transfer RNA, that are able to protect themselves from breakdown by having "hairpin loops" -- places where the helix doubles back and bonds to itself through complementary base-pairing, just like DNA has.

[Image licensed under the Creative Commons Vossman, Pre-mRNA-1ysv-tubes, CC BY-SA 3.0]

The second discovery was that RNA is autocatalytic -- pieces of RNA can actually feed back and speed up the reactions that form more RNA.  DNA doesn't do this, which was a major stumbling block to figuring out how the first self-replicating DNA formed.

So most folks are convinced that RNA was the first genetic material, and that it was only superseded by DNA after first double-stranded RNA formed, and then there was a chemical alteration of the sugar in the backbone (deoxyribose for ribose) and one of the nitrogenous bases (thymine for uracil).  But this only shoved the basic problem back one step.  Okay, RNA came before DNA; but what made the RNA?

We've known for ages, because of the stupendous Miller-Urey experiment, that making nucleotides -- the building blocks of both RNA and DNA -- is easy in the abiotic conditions that existed on the early Earth.  But how did link together into the long chains that form the structure of all functional RNA?

The new research indicates that it's amazingly simple -- all you have to do is to take the solution of nucleotides, and allow it to percolate through the pores of one of the most common rocks on Earth -- basaltic volcanic glass.

This stuff is kind of everywhere.  Not only is ninety percent of all volcanic rock on Earth made of basalt, it's also common on the two other rocky worlds we've studied -- the Moon and Mars.  "Basaltic glass was everywhere on Earth at the time," said Stephen Mojzsis, of the Foundation for Applied Molecular Evolution, who co-authored the study.  "For several hundred million years after the Moon formed, frequent impacts coupled with abundant volcanism on the young planet formed molten basaltic lava, the source of the basalt glass.  Impacts also evaporated water to give dry land, providing aquifers where RNA could have formed."

Basalt also contains two ions that the team showed were critical for forming the RNA nucleotides and then linking them together -- nickel and boron.  The experiments they ran showed that all you had to do was pour the nucleotide slurry over the basaltic glass, and wait -- and voilĂ , in a day or two you had 100- to 200-subunit-long chains of RNA that look exactly like the kind you find in living things.

Given basalt's ubiquity on rocky planets, this makes it even more likely that there is life elsewhere in the universe, and that its biochemistry might have some striking overlap with ours.  Exciting stuff.

So it looks like the quote from the wonderful movie Contact might well turn out to be prescient.  "The universe is a pretty big place. It's bigger than anything anyone has ever dreamed of before. So if it's just us... seems like an awful waste of space."

**************************************

No comments:

Post a Comment