------------------------------------------------------- This Focus Report is extracted from the full-text Email publication SCIENCE-WEEK. Complete SCIENCE-WEEK subscription details are appended to this file. Other SW Focus Reports and information about SCIENCE-WEEK can be found at . ------------------------------------------------------- ------------------------------------------------------- ORIGIN OF LIFE A Summary Group from SCIENCE-WEEK ------------------------------------------------- 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) ------------------- Copyright (c) 1998 Science-Week All Rights Reserved Email: Web: ------------------- SCIENCE-WEEK Subscriptions: ----------------------------------------------- Please note: Educational and other nonprofit institutions and organizations are eligible for group subscription rates for SCIENCE-WEEK: 50+ subscribers at a subscription rate of US$1 per year per subscriber, with SW delivered individually to each Email address. 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