Re: Article: The Origin of Life


Perplexed in Peoria wrote:
<dgenglish@xxxxxxxxxxx> wrote in message news:1156864192.150412.235960@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

Nashton wrote:

snip


Just curious.

Most evolutionists in here and elsewhere claim that there is no reason
for life to tend to become more complicated. They claim that it is a
process lacking any determinism and that given the lack of any need to
"evolve", that organism maintains the status quo ante.

My question is: If a primitive or proto-cell (if there ever were such a
thing) could continue going on with just some RNA as its replicating
material and a simple semi-permeable fatty acid as an envelope could
haver survived in its simple state, why would complexity increase? What
would be the impetus?

Well, even in the absense of some kind of 'drive' toward higher complexity,
it is still the case that if some beneficial increment in useful complexity
arises by chance, natural selection will favor it.

Secondly, how the heck to you get phospholipids out of nothing in the
environment in order to get a proto-cell with a coating? And how likely
is it that these molecules (RNA and phospholipids) could have been in
proximity to somehow merge and create primitive life?

Modern membranes are made from phospholipids, but the original membranes
could have used a different, less effective but easier to make, material.

But I think that your point about putting the RNAs and the membranes
together is a good one. It certainly hasn't been ignored by
abiogenesis speculators, and there are a variety of ideas, but IMO
no good ones. That is why I think that the membranes came first and
had millions of years of evolution to get their act together before
they first tried to incorporate RNA into their act.

Thirdly, it seems to almost always boil down to chicken and egg circular
argument. RNA can't replicate without proteins, proteins can't be
produced with RNA etc., etc.

RNA can be copied from an RNA template without proteins

Johnston, W.K., P.J. Unrau, M.S. Lawrence, M.E. Glasner, and D.P.
Bartel. 2001. RNA-catalyzed RNA- polymerization: Accurate and general
RNA -templated primer extension. Science 292:1319-1325.

proteins can be synthesized from a ribosome, with proteins removed

Science 5 June 1992:
Vol. 256. no. 5062, pp. 1416 - 1419
Unusual resistance of peptidyl transferase to protein extraction
procedures
HF Noller, V Hoffarth, and L Zimniak

proteins can be synthesized from a protein-free ribozyme

Chem Biol. 1998 Oct;5(10):539-53. Related Articles, Links
Peptidyl-transferase ribozymes: trans reactions, structural
characterization and ribosomal RNA-like features.
Zhang B, Cech TR.

Please retract your error.

I agree with dgenglish that "RNA can't replicate without proteins"
may not be a safe position to take. But there is a lot more work
that needs to be done before we can say with any confidence that
this particular chicken-egg problem has been solved. For example,
we don't have ribozymes yet for amino acid synthesis, for attaching
amino acids to their cognate tRNAs, synthesizing nucleotides,
generating energy, etc. etc. Saying that abiogenesis is a solved
problem would definitely be a lie, but saying that abiogenesis
has been shown to be impossible is a lie too.

I certainly agree that the questions of abiogenesis have not yet been
answered.

I imagine that the earliest proteins were not synthesized in a template
dependent manner, but that the polymerization of amino acids served
some other cellular function. Maybe nutrient storage, maybe
aggregation of cellular waste, maybe even providing some RNAase
resistant stabilizer for the ribozymes of the time. Of course that's
only my imagination, and I can't imagine any good experiment to test
these ideas.

Nucleoside synthesis seems to me to be the "black box" of the RNA world
hypothesis. How were nucleosides being formed, at high enough
concentration, to support polymerization?

Dave

.

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