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 (
Proc. Natl. Acad. Sci. US 31 Mar 98 95:3370
Science-Week8 May 98

Related Background:
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;

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-Week2 Jan 98

Science-Week 5 Sep 97

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