Quetzal

Tronvillain: Actually that idea was part of my "stream of consciousness" that led to my silly post above. I had just finished reading about bacterial gene swapping and viral segment insertion in DNA, then started off on a "fantasy tangent" wondering about whether our RNA world hypothesis could have included RNA parasites on other molecules, including other RNA strands (although I was thinking more along the lines of Cairns-Smith's RNA or PNA predecessor overthrow of the Magic Crystal world). Which in turn led to my imagining the possibility that RNA pseudo-viruses could have been at the root of more complex cells. Which of course I managed to conflate with SW's OP... An overactive imagination is a dangerous thing.

However, to reply to your post (finally), I still can't get past the problem about what molecules RNA was the parasite ON. In spite of the rather appealing thought that this scenario
might be a logical extension of SET to the nucleotide level, I haven't seen really compelling evidence that proteins, f'rinstance, evolved first (since they can't self-replicate). I rather fancy the idea that our hypothetical pseudo-virus parasitized other RNA strands (simplistically, a strand that could introduce new RNA into an existing replicator passes on both its code and the replicator's code during replication - remember at this level we are talking almost pure Lamarckian evolution). Look at bacterial "sex" for another bit of inference to support this REALLY speculative model.

I wish the first molecule had evolved camcorders...

CodeMason

You're a bit behind on the times, I'm afraid. Ghadiri showed us, in rather spectucular fashion, that (small, rather simple) peptides can indeed self-replicate.

And let's not forget the cause of mad cow disease.

[ January 11, 2002: Message edited by: CodeMason ]</p>

tronvillain

It doesn't even necessarily have to be a self replicating molecule - it could be a system of catalysts which happens to make most or all of its own components.

Quetzal

Actually, no. I am aware of Ghidiri's work at Scripps. He had to do a fair bit of chemical tweaking to get his protein (and he started with a modern peptide chain) to self-replicate. IMO not all that compelling thus far... This doesn't say it "couldn't" have been done in nature... BTW, Jean Chmielewski at Perdue did something similar.

The work I think holds the most promise is Miller's new synthesis, where an RNA strand gloms on to short peptides and you end up with hybrid PNA. Apparently, PNA is both easier to produce than RNA, and eliminates some of the problems with amino acid/proteins as #1 organism (i.e., chirality, heritable coding, self-replication).

OOL is one of the most controversial and leading edge scenes today.

BTW: if you'd like to read more (non-technical) about the various chemical hypotheses see <a href="http://scicom.ucsc.edu/SciNotes/0001/cooking.htm" target="_blank">this article</a>.

What's that about mad cow?

You still haven't gotten past chirality and excessive variability(not to mention coding - which I suppose could have come later via RNA parasitism?).
[edited to add: Yes, I'm aware that's what Ghidiri's trying to do in the lab - build a "protein ecosystem" to see what happens. I hadn't heard he had gotten much result yet.]

[ January 11, 2002: Message edited by: Morpho ]</p>

CodeMason

For just tinkering with a yeast protein, I believe he did a pretty good job. Whether or not it could form naturally is not the issue (it contains some synthetic amino acids, I believe), it's just the fact that a peptide CAN self-replicate.

Mad cow disease is replicating degenerative protein fragments.

tronvillain

I wouldn't say that prions "replicate" in any meaningful sense of the word.

Morpho: This scenario doesn't require coding - there is no genetic material, just a metabolism that happens to produce most or all of its own catalysts. Perhaps you could elaborate on "excessive variability"?

Oolon Colluphid

Well if not, how do they spread? If copies aren’t being made (ie they're not getting, somehow, replicated), then there are a finite number of them and are being diluted at each act of dissemination. Without checking I’ve no idea, but I was under the impression that that’s not the case.

Cheers, Oolon

Quetzal

No question, it was an awesome experiment - probably almost akin to Cech's discovery of rRNA. I'll be looking forward to the results of his "ecosystem" experiments.

Thanks. I had thought they were still arguing about it. Your post made me look it up. Here's what I found on <a href="http://w3.aces.uiuc.edu/AnSci/BSE/Index_BSE_Info_at_UIUC_Science.htm" target="_blank">this site</a>. This ability lends a lot of credence to your amino-acid world - abnormal proteins that can cause normal ones to fold abnormally meets the criteria for replicatability. Can you point to any site that might have research/speculation that prions were organic precursors?

"Excessive variability" is one of the arguments Cech uses against the protein world hypothesis: (from the website I cited in my last post).

Hey guys, slow down. I don't have a particular vested interest in any of the two theories (RNA World, Protein World). I'm leaning toward Miller's PNA -&gt; RNA hypothesis 'cause it seems to solve a lot of the questions about synthesis, catalysis, self-replication, variance, heritability. I'll have to do some more reading about prions to see if there's a conflict.

One question I still have about both ideas is how much they depend on high concentrations of precursor chemicals or specific atmospheric or environmental conditions.

Once we hit RNA, everything else is just evolution.

theyeti

It's unlikely that prions as we know them today were organic precursors to modern organisms. Prions are only able to catalyze the change of a similar protein into themselves. But they can't form that similar protein de novo. Some other process would have to form that protein, be it a self-replicase or a primitive ribosome, and it would be these things that would be precursors to modern life. Of course, prions could always play a tangenital role by increasing the concentration of certain catalyists, etc.

theyeti

tronvillain

That site isn't talking about what I'm talking about.