From: rwallace@unix1.tcd.ie (russell wallace)
Subject: Re: Biogenesis (was: ETs and Radio)
Organization: Trinity College, Dublin
Date: Thu, 30 Jul 1992 22:25:54 GMT

In <SJE.92Jul30115800@xylos.ma30.bull.com> sje@xylos.ma30.bull.com (Steven J. Edwards) writes:

>#> 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?

>This is trivally answered: first, the synthesized products do not
>merely float away because they have assorted polar regions that can
>interact with the synthesizer, and second, other similar or identical
>replicators nearby would share in the benefit of peptide production
>from other than themselves.

I don't think polar regions by themselves are enough to stop the amino
acids floating away pretty quickly. And why should nearby pieces of RNA
be similar or identical? If you answer, because the original piece of
RNA used amino acids to replicate itself, then this is begging the
question, because the point at issue is can you get something capable of
non-trivial self-replication.

># 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.

>All chemical reactions require energy to start; this is called the
>"activation energy" of a reaction.  There are several natural sources,
>some of these are: photons from the Sun, ambient kinetic energy
>(heat), stored chemical energy from previously producted compounds,
>and lightning.

Sure. Now how is an RNA cluster actually going to go about tapping this
energy to synthesize amino acids, without already having a complex set
of enzymes?

>#> 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?

>Again, the peptides do not just "float away"; peptides that did get
>loose would benefit similar (or identical) replicators.  These
>secondary replicators would likely be physically close anyway.

Again, why are nearby replicators similar, unless you previously assume
that the RNA cluster is capable of non-trivial self-reproduction?

># you *still* need the full machinery for non-trivial self-reproduction.

>No.  Simple RNA replicator molecules can do it with only naturally
>occuring amino acid molecules.  Complex RNA replicators may synthesize
>some to all of the needed amino acids (and other molecules).

Has an RNA cluster unsupported by enzymes been demonstrated to
synthesize amino acids or peptide chains (actually, stringing amino
acids together into proteins is more important, because there would be
plenty of amino acid molecules already floating around)?

># 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?

>Information necessary for early replication does not need the "full
>transcription apparatus" because it is not based on any genetic code.
>Early RNA replicators had their replication information stored in
>their three dimensional structure, not in any one dimensional coded
>strand.  RNA chains act as sort of a "poor man's emzymes": there are
>only four bases instead of dozens of amino acids, but there still is a
>lot that can be accomplished.  Laboratory results show that: both RNA
>and amino acids form under natural conditions, complex RNA structures
>form spontaneously, some these structures have the power of
>replication and peptide synthesis.  Of course, none of the early
>replicators had the efficiency and fidelity of today's genetic
>apparatus.  But they didn't need it either.

Hmmm... this is interesting; you're saying that an RNA cluster could
double as blueprint *and* machinery, thereby making things a lot easier.
However, you would still seem to have the problem that the RNA cluster
must eventually get around to synthesizing some proteins that are going
to assist it in replication, and these would tend to drift away before
being much use. How much of this has been demonstrated so far?

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