A better shortcut to the genetic code?

December 24, 2017 4:10 PM

A popular theory holds that life emerged from a rich chemical soup in which RNA was the original self-replicator. But a combination of peptides and RNA might have been more effective.
posted by Rumple (3 comments total)

Cannonically, RNA is typically very short lived and unstable. Part of that is the inherent chemical instability (reactivity) of long string RNA molecules. The other (perhaps larger part) is that proteins (enzymes) that degrade RNA are ubiquitous and probably derive from very diverse origins.

I wouldn't be surprised if "life" precursors were RNA based, using proteins as their effectors but once DNA based templates for long string proteins that could fold into 3D shapes were established, would blossom.

The article mentions, but short shrifts lipids; micelles (single layer lipid "bubbles) are pretty easy; lipid bilayers are comparatively complex to achieve without some kind of entropy-busting mechanism. Most cells of known living organisms is based on lipid biyalers (sometimes supplemented with other molecular-level structures such as cellulose in plant cell walls) and this method of compartmentalization allows proteins and the small molecules that they interact with do.... do their things.

Where these lipids come from - they're now from proteins that break down and assemble and regulate the transport these fundamental cellular structures - is another mystery.

My feeling is that - all of these processes are unlikely to develop from chaos, but once the unlikely event occurs as a self-perpetuating event, the self-perpetuation opens the possibility of further stabilization events.

My point, I guess, is that RNA may very well have been, from a organic chemistry equilibrium angle, be both the initiator of "life" and something that evolved "life" is wary about - viability requires an enormous amount of chance (but once you "win the lottery" there are chemical/biochemical [and numbers; we're talking about events exceeding the number of stars in the galaxy by many magnitudes every second] that help perpetuate "life") but once you have the system up, big variability is a bad thing (it disrupts systems that are self-perpetuating).

In that context, it kind of makes sense that there are so many biological systems that explicitly breaks down RNA (in addition to anti- RNA- based viruses immune strategies in virtually all organisms... which is a large part of the basis of my rant here).

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So, yeah, this is interesting (and someone might be advancing their journalism career and might possibly be worth following) but nothing particularly groundbreaking or enlightening.
posted by porpoise at 6:01 PM on December 24, 2017 [6 favorites]

I thought the neat part was they found a minimal RNA code that's effectively self-referential, because that RNA encodes for two proteins that, voila, decode that RNA into the same two proteins. There's some very convoluted theoretical computer science (Quine, Godel) behind this (why this process constitutes self-referential) so my sense is these researchers are saying that any account of abiogenesis (is this the usual term?) has to be sound on computational and information theoretic foundations. It motivates the question of, How did the genetic code, a mathematical function from the set of codons to the set of amino acids, arise, and the reflexivity is what makes this abstraction emergent out of lower, biochemical processes (hence the inability of the conventional RNA story to explain this).
posted by polymodus at 7:19 AM on December 25, 2017

Prepare to have your mind blown then; a lot of viral protein/enzyme encoding nucleic acid sequences can be partial palindromes (the tail of one enzyme shares the reverse nucleic acid sequence to the head of another enzyme, read in the opposite direction) and multiple genes can be transcribed from the same sequence (not to mention splice recombination).

If this is your thing, I'd suggest looking up transposons.
posted by porpoise at 8:30 PM on December 26, 2017 [1 favorite]