From: sje@xylos.ma30.bull.com (Steven J. Edwards)
Subject: Re: Biogenesis (was: ETs and Radio)
Reply-To: sje@xylos.ma30.bull.com
Organization: Bull HN, Worldwide Information Systems, Billerica, Mass., USA
Date: 30 Jul 92 11:58:00
	<1992Jul28.105743.29096@news.Hawaii.Edu>
	<rwallace.712328556@unix1.tcd.ie> <1992Jul29.162909.3574@ke4zv.uucp>
	<rwallace.712441800@unix1.tcd.ie>
	<SJE.92Jul29183135@xylos.ma30.bull.com>
	<rwallace.712483849@unix1.tcd.ie>

In article <rwallace.712483849@unix1.tcd.ie> rwallace@unix1.tcd.ie (russell wallace) writes:
#> In article <rwallace.712441800@unix1.tcd.ie> rwallace@unix1.tcd.ie (russell wallace) writes:
#>#  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?

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.

# 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.

#> 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.

# 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).

# 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.

No cell like membranes are needed.  No DNA is needed.  No tricky DNA
synthesis and transcription enzymes are needed.  No genetic code is
needed.  None of these are needed for "first life".  All of these can
be evolved from the early replicators.

There is no need for a special miracle for Earth, therefore it is
unlikely that Earth is the only life bearing planet.  If there is a
miracle, then it is the creation of a universe with physical laws that
permit (actually, strongly encourage) development of replicators and
intelligence.

This thread should probably be continued in the talk.origins
newsgroup.

 [The above opinions expressed are my own; not necessarily held by others.]
      == Steven J. Edwards           Bull HN Information Systems Inc. ==
      == (508) 294-3484              300 Concord Road         MS 820A ==
      == sje@xylos.ma30.bull.com     Billerica, MA 01821          USA ==
"That Government which Governs the Least, Governs Best." -- Thomas Jefferson