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Subject: SW Focus Report November 13, 1998
Date: Wednesday, November 11, 1998 6:45 PM

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ORIGIN OF LIFE

A Summary Group from SCIENCE-WEEK
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ORIGIN OF LIFE: PRODUCTION OF PEPTIDES ON INORGANIC SURFACES
The primordial process responsible for the activation of amino
acids and the formation of peptides under primordial conditions
is one of the great riddles of the origin of life. ... ... Huber
and Wachterschauser (Technische Universitat Munchen, DE) now
report that in experiments modeling volcanic or hydrothermal
settings, amino acids were converted into their peptides by use
of coprecipitated (Ni,Fe)S and CO in conjunction with H(sub2)S
(or CH(sub3)SH) as a catalyst and condensation agent at 100
degrees centigrade and pH 7 to 10 under anaerobic aqueous
conditions. The amino acids involved in the experiments were
phenylalanine, tyrosine, and glycine. The authors suggest their
results demonstrate that amino acids can be activated under
geochemically relevant conditions, and that the results support a
thermophilic origin of life with a primordial surface metabolism
on transition metal sulfide minerals. They further suggest that a
continuously recycling library of peptides was generated on the
surfaces of a library of (Fe,Ni)S structures, and that the
results raise the possibility that CO and Ni had a much greater
role in the primordial metabolism than in any of the known extant
metabolisms. They point out that all known extant organisms are
found in habitats with low activities of CO and Ni, and they
suggest this could explain why organisms resorted to the
formation of CO from CO(sub2) and to the elimination of nickel
from many enzymes.
QY: Gunter Wachterschauser, Tal 29, D-80331 Munchen, DE.
(Science 31 Jul 98 281:670) (Science-Week 28 Aug 98)


PREBIOTIC ORGANIC COMPOUNDS: OCEANIC PROTECTION FROM SOLAR UV
It is generally believed that the Earth's primitive atmosphere
lacked oxygen, and therefore that an ozone layer protective
against ultraviolet radiation did not exist. This is considered
to be a serious problem for the accumulation of prebiotic organic
compounds on Earth and on Mars, and this problem would have been
worsened by the theoretically expected elevated ultraviolet
radiation production of the early Sun. Protection from
ultraviolet radiation is one of the motivations for proposing an
origin of life in submarine vents, benthic regions, and in deep
subsurface environments. Most attempts to deal with this problem
have involved atmospheric absorbers such as H(sub2)S, SO(sub2),
S(sub8), and organic hazes. ... ... Cleaves and Miller
(University of California San Diego, US) present an analysis of
the problem and report that even in the absence of atmospheric
shielding there would have been sufficient ultraviolet absorbers
in the ocean to allow for the accumulation of organic material.
These absorbers include organic polymers from electric discharges
and hydrogen cyanide polymerizations, solubilized elemental
sulfur, and inorganics such as Cl(-), Br(-), Mg(2+), SH(-),
Fe(2+). Complete ultraviolet protection could also be provided by
a frozen ocean, an oil slick, or large amounts of organic foams.
The authors suggest that oceanic ultraviolet protectors increase
the size of planetary habitable zones and thereby increase the
number of planets on which life may have arisen.
QY: Stanley L. Miller 
(Proc. Natl. Acad. Sci. US 23 Jun 98 95:7260)
(Science-Week 17 Jul 98)


ORIGIN OF LIFE: A MODEL FOR THE UNIVERSAL ANCESTOR
Biologists have long subscribed to the idea that all life on
Earth arose from a common ancestor. Until recently, nothing
concrete was said about this ancestor, but it was intuitively
assumed to be simple, often likened to a *prokaryote, and
generally held to have had little or no *intermediary metabolism.
Only when biology became defined on the level of molecular
sequences did it become possible to seriously consider the nature
of this ancestor. ... ... Carl Woese (University of Illinois
Urbana-Champaign, US) presents a "genetic annealing" model for
the universal ancestor of all extant life. Physical annealing
involves a first stage heating to a high temperature followed by
a slow cooling of the system to produce new structures,
particularly special crystalline forms. The term "annealing" is
also used in molecular biology to refer to the separation of DNA
strands by heating and the recombination of complimentary strands
by cooling. In Woese's model, the term "annealing" is used in
still a third sense. In the author's model, in the evolutionary
counterpart of physical annealing, the elements of the system are
primitive cells, mobile genetic elements, and so on, and physical
temperature becomes "evolutionary temperature", the evolutionary
"tempo". The evolutionary analog of "crystallization" is
emergence of new structures, new cellular subsystems that are
refractory to major evolutionary change. The author defines the
entities in which *translation had not yet developed to the point
that proteins of the modern type could arise as "progenotes", and
the era during which these were the most advanced forms as the
"progenote era". Concerning "evolutionary temperature", the
author points out that macroscopic evolutionists recognized long
ago a relationship between the "tempo" (rate) of evolution and
its "mode" (a measure of the outcomes). When microbial evolution
finally came into the picture, a similar phenomenon was
encountered on the molecular level, suggesting that this
tempo/mode relationship was a fundamental manifestation of the
evolutionary process. Because of high mutation rates and other
factors, the progenote era is proposed as one of very high
evolutionary tempo. In the author's model, progenotes were very
unlike modern cells, their component parts with different
ancestries, and the complexion of their components changing
drastically over time. Progenotes possessed the machinery for
gene expression and genome replication and at least some
rudimentary capacity for cell division, but the ordinary cellular
functions had no genealogical continuity, since they were too
subject to the confusion of *lateral gene transfer. According to
the author, the transition from progenotes to genotes turned upon
the evolution of translation, the conversion of messenger RNA
code into the specific amino acid sequences of specific proteins.
The author proposes the genetic annealing model as "an attempt to
develop a consistent general picture of the universal ancestor...
The ancestor cannot have been a particular organism, a single
organismal lineage. It was communal, a loosely knit, diverse
conglomeration of primitive cells that evolved as a unit... The
universal ancestor is not an entity, not a thing. It is a process
characteristic of a particular evolutionary stage." The author
concludes with a conjecture that genomes resulting from episodes
of rapid evolution will contain an abnormally high proportion of
foreign genes, and a suggestion that "genome sequences will soon
be available in sufficient number to properly test whether the
tempo/mode relationship (rapid evolution) invariably links
increased mutation rate and increased levels of lateral gene
transfer or vice versa."
QY: Carl Woese (carl@ninja.life.uiuc.edu)
(Proc. Natl. Acad. Sci. US 9 Jun 98 95:6854)
(Science-Week 3 Jul 98)
... ... *prokaryote: Prokaryotes are cells without a cell nucleus
and other membrane-bound organelles.
... ... *intermediate metabolism: The sum of all metabolic
reactions between the uptake of nutrients and the excretion of
waste products.
... ... *lateral gene transfer: This refers to the "horizontal"
transfer of genetic information between individuals of the same
generation, the mechanism involving the incorporation by the
genome of accessible new genetic elements. The process is common
among primitive life forms such as bacteria.
-------------------
Related Background:
BIOCHEMICAL EVOLUTION: POLYMERIZATION ON MINERAL SURFACES
J. Smith (University of Chicago, US) proposes a conceptual
framework for consideration of the origins of replicating
biopolymers. Although extended Darwinian natural selection
coupled with Mendel-Watson-Crick genetic inheritance/mutation
provides a plausible framework for integrating the patchy
paleontological record with the increasingly complex biochemical
zoo of the present Earth, the actual chemical beginning of "life"
still poses major challenges. How could the first replicating and
energy-supplying molecules have been assembled from simpler
materials that were undoubtedly available on the early proto-
continents? Catalysis at mineral surfaces might generate replic-
ating biopolymers from simple chemicals supplied by meteorites,
volcanic gases, and photochemical gas reactions. But many ideas
are implausible in detail because the proposed mineral surfaces
strongly prefer water and other ionic species to organic ones.
The molecular sieve silicalite (Union Carbide; = Al-free Mobil
ZSM-5 zeolite) has a 3-dimensional 10-ring channel system whose
electrically neutral silicon-oxide surface strongly adsorbs
organic species over water, and the ZSM-5 type zeolite mutinaite
has recently been found in Antarctica. The author proposes that
zeolites with similar structures may have existed on the surface
of Earth during its life-origin phase, and that polymer migration
along weathered silicic surfaces of micrometer-wide channels of
feldspars might have led to assembly of replicating catalytic
biomolecules and perhaps primitive cellular organisms. The author
suggests that weakly metamorphosed Archaean rocks might retain
microscopic clues to the proposed mineral adsorbent/catalysts,
and that other frameworks are also possible, including ones with
laevo/dextro one-dimensional channels.
QY: Joseph V. Smith (smith@geol.uchicago.edu)
(Proc. Natl. Acad. Sci. US 31 Mar 98 95:3370)
(Science-Week 8 May 98)
-------------------
Related Background:
ORIGIN OF LIFE: THE PRESENT STATUS OF CHEMICAL THEORY
The essential question involved in the origin of what we call
life is how can order arise from disorder? At the present time,
this question is approached on two fronts: 1) study of the
principal features of self-organizing systems, systems in which
order does arise from disorder, systems in which order is indeed
demanded from disorder on thermodynamic grounds; and 2) study of
the detailed chemistry of such systems, the chemistry of
organization and the chemistry of components. In the case of
components, it is essential that appropriate self-organizing
components exist in the first place if they are to become self-
organized, and such candidate components are thus the focus of
much chemical research in this area. In 1953, the chemist Stanley
Miller reported what soon became a famous experiment. To water
under a gas mixture of methane, ammonia, and hydrogen, he added
an electrical discharge. After one week of continuous electrical
discharge, he found that a number of important biological
molecules, including amino acids, had been formed. Miller
proposed his experiment as a model for the conditions under which
the essential compounds necessary for life originated . The
Miller experiment was a watershed, and it began a new era of
experimentation and analysis of possible primordial components.
Coupled with this, were the new important discoveries by
astrophysicists of the presence of organic molecules in the
interstellar medium and in meteorites. In a review of origin of
life theories, P. Radetsky (Univ. of California Santa Cruz, US)
points out that the Miller theory is no longer the consensus
theory, that contemporary geologists believe the primordial
atmosphere consisted primarily of carbon dioxide and nitrogen,
which are less reactive than the gases in the Miller experiment,
and that the field is currently embroiled in controversy fueled
for the most part by an absence of hard fact. QY: Peter Radetsky,
Univ. of California Santa Cruz 408-429-4008 (Earth February 1988)
(Science-Week 2 Jan 98)
-------------------
Related Background:
RNA POLYMERIZATION A FOCUS AT ORIGIN OF LIFE MEETING
If the complex molecules necessary for life originated on Earth
rather than elsewhere, then a natural question is how? How and
under what conditions did the first polymerizations occur? Under
ordinary laboratory conditions, without special outside agencies
such as catalysts, RNA monomers, for example, will not assemble
into polymers unless the monomer concentration is impossibly
large. So how was polymerization achieved on the early Earth?
Such questions are now the essential questions in the origin-of-
life branch of biological science, and at a recent regional
meeting of the American Chemical Society, a group of researchers
in this area presented results of their latest studies. David
Usher et al have used a "day-night machine", an apparatus that
exposes solutions to alternating cycles of daylight and darkness,
and have apparently found evidence of RNA polymerization from
monomers, the polymerization dependent on the alternating cooling
and heating produced by the light-dark cycles. James Ferris and
Gozen Ertem (Rensselaer Polytechnic Institute, NY US) presented
evidence that clay or pyrite minerals can catalyze polymer
formation from RNA monomers by serving as adsorption templates.
And Tom Waddell et al (University of Tennessee Chattanooga, US)
reported that if intermediates of the citric acid cycle, so vital
in biological processes, are exposed to sunlight, the production
of other intermediates in the cycle is catalyzed. The hunt for
efficient catalysts for RNA polymerization that may have been
present on primeval Earth continues.
(Science 22 Aug 97) (Science-Week 5 Sep 97)

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