Homochirality through Photon-Induced Melting of RNA/DNA: the Thermodynamic Dissipation Theory of the Origin of Life

The homochirality of the molecules of life has been a vexing problem with no generally accepted solution to date. Since a racemic mixture of chiral nucleotides frustrates the extension and replication of RNA and DNA, understanding the origin of homochirality has important implications to the investigation of the origin of life. Theories on the origin of life have generally elected to presume an abiotic mechanism giving rise to a large prebiotic enantiomer enrichment. Although a number of such mechanism have been suggested, none has enjoyed sufficient plausibility or relevance to be generally accepted. Here we suggest a novel solution to the homochirality problem based on a recently proposed thermodynamic dissipation theory for the origin of life. The ultraviolet absorption and dissipation characteristics of RNA/DNA point to their origin as photoautorophs, their replication assisted by UV light and temperature, and acting as catalysts for the global water cycle. Homochirality is suggested to have been incorporated gradually into the emerging life as a result of asymmetric right- over left-handed photon-induced denaturation of RNA/DNA occurring when Archean sea surface temperatures became close to the denaturing temperatures of RNA/DNA. This differential denaturing success would have been promoted by the somewhat right-handed circularly polarized submarine light of the late afternoon when surface water temperatures are highest, and a negative circular dichroism band extending from 220 nm up to 260 nm for small segments of RNA/DNA. A numerical model is presented demonstrating the efficacy of such a mechanism in procuring 100% homochirality of RNA or DNA from an original racemic solution in less than 500 Archean years assuming a photon absorption threshold for replication representing the hydrogen bonding energy between complementary strands. Because cholesteric D-nucleic acids have greater affinity for L-amino acids due to a positive structural complementarity, and because D-RNA/DNA+L-amino acid complexes also have a negative circular dichroism band between 200 - 300 nm, the homochirality of amino acids can also be explained by the theory

Fundamental Molecules of Life are Pigments which Arose and Evolved to Dissipate the Solar Spectrum

The driving force behind the origin and evolution of life has been the thermodynamic imperative of increasing the entropy production of the biosphere through increasing the global solar photon dissipation rate. In the upper atmosphere of today, oxygen and ozone derived from life processes are performing the short wavelength UVC and UVB dissipation. On Earth's surface, water and organic pigments in water facilitate the near UV and visible photon dissipation. The first organic pigments probably formed, absorbed, and dissipated at those photochemically active wavelengths in the UVC that could have reached Earth's surface during the Archean. Proliferation of these pigments can be understood as an autocatalytic photochemical process obeying non-equilibrium thermodynamic directives related to increasing solar photon dissipation rate. Under these directives, organic pigments would have evolved over time to increase the global photon dissipation rate by; 1) increasing the ratio of their effective photon cross sections to their physical size, 2) decreasing their electronic excited state life times, 3) quenching non-radiative de-excitation channels (e.g. fluorescence), 4) covering ever more completely the solar spectrum, and 5) dispersing into an ever greater surface area of Earth. From knowledge of the evolution of the spectrum of G-type stars, and considering the most probable history of the transparency of Earths atmosphere, we construct the most probable surface solar spectrum as a function of time and compare this with the history of molecular absorption maxima obtained from the available data in the literature. This comparison supports the thermodynamic dissipation theory for the origin of life, constrains models for Earth's early atmosphere, and sheds some new light on the origin of photosynthesis.Comment: 43 pages, 3 figure

A Dissipative Photochemical Origin of Life: The UVC Abiogenisis of Adenine

I describe the non-equilibrium thermodynamics and the photochemical mechanisms which may have been involved in the dissipative structuring, proliferation and evolution of the fundamental molecules at the origin of life from simpler and more common precursor molecules under the impressed UVC photon flux of the Archean. Dissipative structuring of the fundamental molecules is evidenced by their strong and broad wavelength absorption bands and rapid radiationless dexcitation in this wavelength region. Proliferation arises from the auto- and cross-catalytic nature of the intermediate products. Evolution towards states of concentration profiles of generally increasing photon disspative efficacy arises since the system has numerous stationary states, due to the non-linearity of the photochemical and chemical reactions with diffusion, which can be reached by amplification of a molecular concentration fluctuation near a bifurcation. An example is given of photochemical dissipative abiogenisis of adenine from the precursors HCN and H$_2$O within a fatty acid vesicle on a hot ocean surface, driven far from equilibrium by the impressed UVC light. The kinetic equations are resolved under different environmental conditions and the results analyzed within the framework of Classical Irreversible Thermodynamic theory.Comment: 42 pages, 17 figure

Transpiration in plants: A thermodynamic imperative

In this article we determine the importance of transpiration in plants at three different levels of organization: the plant itself, the ecosystem, and the biosphere, all in terms of entropy production due to transpiration. We propose that transpiration is a thermodynamic imperative rather than a physiological burden for the plant. Plants have not replaced their prevalent metabolism C3 with those of less loss of water, C4 or CAM. We argue that the fact that plants retain higher rates of transpiration along evolution could be explained using thermodynamic criteria.
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