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A biogeochemical model for the evolution of template-and-sequence-directed (TSD) syntheses of biological templates (proto-RNAs) and catalysts (peptides) is described. A fluctuating environment characterized by hydrating (cool) and dehydrating (warm) phases with cycles of consecutive organic reactions, as well as a constant supply of the polymeric building blocks is assumed. The scenario starts with the catalyzed formation of a primordial population of small random peptides, based on the relatively-ineffective mineral catalysts. The resulting peptides initiate a catalytic takeover process, during which the catalytic functions are gradually taken over by peptides. The evolution of TSD peptides is based on a combination of Lahavs (1991) co-evolution and Möller and Janssen's (1990) specific recognition sites hypotheses. During the emergence of TSD systems the fraction of TSD peptides and proto-RNA constituents rises from almost insignificance to dominance in a TSD Reactions Takeover. The TSD system is characterized by autocatalysis, positive feedback loops and a primordial genetic code. The model is the basis for a computer program (Part II of present series). 相似文献
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Lowering of Endogenous Lipoxygenase Activity in Pisum sativum Foliage by Cytokinin as Related to Senescence 总被引:3,自引:0,他引:3
Cytokinin (CK), when applied to intact pea plants, considerably lowered endogenous lipoxygenase levels. Furthermore it was demonstrated that the triggering of senescence induced by leaf detachment was invariably accompanied by a significant increase of lipoxygenase activity and the CK application considerably decelerates lipoxygenase increment. It is suggested that the lipoxygenase repression induced by CK is a contributing mechanism to the overall antisenescence action of the hormone, and that this may have biological implications. 相似文献
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