From: rwallace@unix1.tcd.ie (russell wallace)
Subject: Re: Biogenesis (was: ETs and Radio)
Organization: Trinity College, Dublin
Date: Thu, 30 Jul 1992 08:10:49 GMT

In <SJE.92Jul29183135@xylos.ma30.bull.com> sje@xylos.ma30.bull.com (Steven J. Edwards) writes:

>In article <rwallace.712441800@unix1.tcd.ie> rwallace@unix1.tcd.ie (russell wallace) writes:
># In <1992Jul29.162909.3574@ke4zv.uucp> gary@ke4zv.uucp (Gary Coffman) writes:
>#
>#> When you place hydrogen and oxygen together in a 2:1 ratio and provide 
>#> an energy source, what happens? Blooey! Every time? Yes, every time. 
>#> That's the way it is with life chemicals, there is nothing accidental 
>#> about their combination.  It's just basic organic chemistry at work. 
>#> We have very good evidence that the primordial chemical mixtures of
>#> early planetary bodies contain the proper precursor compounds and
>#> elements in abundance. We know that solar UV and electrical discharges, 
>#> lightning, will supply the necessary energy. We've done it in a test tube. 
>#> We haven't yet made the step to the enclosed cell, but with 10^23 precursor
>#> molecules in every cubic meter, the combination is bound to occur.
>#
># Yes, I realize that amino acids are bound to form under the appropriate
># conditions. However, those amino acids are no more likely to
># spontaneously assemble into a life form than 10^6 transistors placed in
># a box and shuffled around are to assemble themselves into a working
># computer.

>The current leading theory is that ribonucleic acids were the first
>step ont he biogenesis chain.  A recent (early 1992.07) issue of
>_Science_ had a very convincing article about self assembly of
>replicating clusters of pure and nearly pure RNA molecules.  It turns
>out that a regular ribosome (protein assembler) is still remarkably
>functional even when almost all of its structural amino acids are
>removed.  Before this research, many scientists had a deep suspicion
>that nucleic acids, either DNA or RNA, got the ball started; now we
>have experimental evidence.

>Therefore, there is now no need to appeal to deep time and large
>reaction volumes for complex protein self assemblers and self
>replicators: the RNA molecules got there first.

>A suggested scenario:

>1) Significant quantities of single or small chain amino acids form
>spontaneously, but no "wonder molecule" replicator is seen.

>2) Ancestral variants of rRNA molecules form clusters spontaneously;
>these have partial replicative ability in varying degrees.  Cluster
>replication is irregular and probably not too accurate as far as
>faithful duplication of the parent template.

>3) Some rRNA clusters are capable of incorporating naturally formed
>amino acid chains.  Some of these cases the amino acids enhance
>replicative fidelity and productivity; natural selective pressure
>begins due to limited supplies of spontaneously formed amino acids.

>4) At some point an rRNA replicating cluster using amino acids becomes
>capable of partial synthesis of useful amino acids.  This replicator
>gains a tremendous advantage over imperfect and less efficient
>replicators who must compete for the limited spontaneous amino acid
>production.

Why would it gain an advantage, given that without a cell membrane, the
amino acids it synthesizes would float away to benefit the other
clusters just as much as the synthesizer?

As a matter of interest, just how could an RNA cluster synthesize amino
acids? From what raw materials? I thought synthesizing amino acids
required energy, and therefore a complex set of enzymes to extract that
energy from something.

>5) The protein making rRNA clusters become self sufficient and the
>first true ribosomes are the result.  This is a good candidate for
>"first life".

Yes, it certainly would be, except the problems again arise:

without a cell membrane, how would the "first life" cluster gain an
advantage, when all its carefully synthesized enzymes floated away to
benefit other replicators?

you *still* need the full machinery for non-trivial self-reproduction.
This means that the RNA must serve as a blueprint carrying the
information to synthesize the proteins which assist with the synthesis
of proteins and the replication of the RNA. What is the simplest system
capable of doing all this, and is it simple enough to have a reasonable
probability of falling together by chance? I don't think so. Why would
you not require the full transcription apparatus?

--
"To summarize the summary of the summary: people are a problem"
Russell Wallace, Trinity College, Dublin
rwallace@unix1.tcd.ie