Influence of ionic inorganic solutes on self-assembly and polymerization processes related to early forms of life: implications for a prebiotic aqueous medium

A commonly accepted view is that life began in a marine environment, which would imply the presence of inorganic ions such as Na+, Cl-, Mg2+, Ca2+, and Fe2+. We have investigated two processes relevant to the origin of life--membrane self-assembly and RNA polymerization--and established that both are adversely affected by ionic solute concentrations much lower than those of contemporary oceans. In particular, monocarboxylic acid vesicles, which are plausible models of primitive membrane systems, are completely disrupted by low concentrations of divalent cations, such as magnesium and calcium, and by high sodium chloride concentrations as well. Similarly, a nonenzymatic, nontemplated polymerization of activated RNA monomers in ice/eutectic phases (in a solution of low initial ionic strength) yields oligomers with > 80% of the original monomers incorporated, but polymerization in initially higher ionic strength aqueous solutions is markedly inhibited. These observations suggest that cellular life may not have begun in a marine environment because the abundance of ionic inorganic solutes would have significantly inhibited the chemical and physical processes that lead to self-assembly of more complex molecular systems.     

狮子王辛巴的荣耀

寒流袭击的那天,没有冬天的广州突然出奇的寒冷。面对中国百年不遇的寒冷天气,我选择了逃离。连续飞行了14小时,穿越了5个时区,我降落在南半球被阳光燃烧着的肯尼亚首都内罗毕(NAIROBI)。我和一个中国人以及两个法国人,带上本地的黑人司机、厨师和充足的食品、水以及扎营设备,开着那辆带天窗的专业狩猎远征(SAFARI)越野车,做一次彻底的狩猎远征。     

伊朗 谜一样的国度

电视中,每天都有关于伊朗的报道,伴随美国要打击伊朗的叫嚣,让人有种大战迫在眉睫的紧张。我唯恐伊朗再不去,这个国家就会像伊拉克一样,彻底改变当今的面貌。于是在好友的帮助下,展开了这次向往已久的伊朗之行。     

Eutectic phases in ice facilitate nonenzymatic nucleic acid synthesis

Polymeric compounds similar to oligonucleotides are relevant to the origin of life and particularly to the concept of an RNA world. Although short oligomers of RNA can be synthesized nonenzymatically under laboratory conditions by second-order reactions in concentrated solutions, there is no consensus on how these polymers could have been synthesized de novo on the early Earth from dilute solutions of monomers. To address this question in the context of an RNA world, we have explored ice eutectic phases as a reaction medium. When an aqueous solution freezes, the solutes become concentrated in the spaces between the ice crystals. The increased concentration offsets the effect of the lower temperature and accelerates the reaction. Here we show that in the presence of metal ions in dilute solutions, frozen samples of phosphoimidazolide-activated uridine react within days at -18 degrees C to form oligouridylates up to 11 bases long. Product yields typically exceed 90%, and approximately 30% of the oligomers include one or more 3'-5' linkages. These conditions facilitate not only the notoriously difficult oligouridylate synthesis, but also the oligomerization of activated cytidylate, adenylate, and guanylate. To our knowledge, this represents the first report to indicate that ice matrices on the early Earth may have accelerated certain prebiotic polymerization reactions.