生物谷: 尽管科学家已经知道,生命出现在地球之前,必先有一些原始代谢机制,或类似RNA复制机制的物体存在。但究竟这些机制,一开始是如何产生的呢? 针对这问题,两位UCSF的科学家,提出了一个模型来说明,简单的化学及物理变化也许就足以构成基础的生命。这份研究将发表在近期的PNAS期刊。
Ken Dill博士说:此模型要阐述的基本观念就是,酵素之间简单的化学反应是可以在微矩规模(micro scale)下的天择过程中进行。一般所谓的天择过程是指,在不同生物体上随机出现特征,藉由竞争或合作留下最能适应环境的条件,接着该条件透过遗传,而出现在更多生命体。而这份研究中,认为酵素间的化学反应,也具有天择般类似的过程: 例如竞争,合作,创新,及对稳定的偏好。
Dill称这种过程叫做“随机的创新”(random innovation),也就是随机反应并无意的创造出一个稳定的复合物。举例来说,两个在溶液中具有不同催化功能的催化剂A及B,是有可能形成所谓的综合体AB。关键在于,如果催化剂A能在反应过程中,释放出催化剂B所需使用到的成分,且如果催化剂B周围没有其他物体能提供这样的成分,则催化剂A及B终究会聚在一起,而成为一种综合AB。藉由这例子,可以显示出为何一系列简单的化学反应,最后有可能形成一个巨大而复杂的分子结构。
长久以来,在生命起源的议题上,促成那些没有自我意识的化学物,组成精巧生化反应的原因,一直是一个谜。而如今,这份研究,提出了一个可能的答案,就是“天择驱动了这个过程”。 (援引华文生技网)
原始出处:
Published online before print June 4, 2007, 10.1073/pnas.0703522104
PNAS | June 12, 2007 | vol. 104 | no. 24 | 10098-10103
BIOLOGICAL SCIENCES / EVOLUTION
Stochastic innovation as a mechanism by which catalysts might self-assemble into chemical reaction networks
Justin A. Bradford, and Ken A. Dill,
Graduate Group in Biophysics and Department of Pharmaceutical Chemistry, University of California, San Francisco, CA 94143
Communicated by Christian de Duve, Christian de Duve Institute of Cellular Pathology, Brussels, Belgium, April 16, 2007 (received for review June 29, 2006)
Abstract
We develop a computer model for how two different chemical catalysts in solution, A and B, could be driven to form AB complexes, based on the concentration gradients of a substrate or product that they share in common. If A's product is B's substrate, B will be attracted to A, mediated by a common resource that is not otherwise plentiful in the environment. By this simple physicochemical mechanism, chemical reactions could spontaneously associate to become chained together in solution. According to the model, such catalyst self-association processes may resemble other processes of "stochastic innovation," such as Darwinian evolution in biology, that involve a search among options, a selection among those options, and then a lock-in of that selection. Like Darwinian processes, this simple chemical process exhibits cooperation, competition, innovation, and a preference for consistency. This model may be useful for understanding organizational processes in prebiotic chemistry and for developing new kinds of self-organization in chemically reacting systems.
chemical evolution | self-organization | abiogenesis | catalytic chains
Fig. 1. Agents (lettered circles) and resources (numbered squares). (a) Agent of type A converts substrate 1 to product 2. (b) Agent of type B converts substrate 2 to product 3. (c) When agents A and B are complexed together, two reactions are chained together, converting substrate 1s to product 3s.
Fig. 1 shows an example. Agent A converts a substrate 1 to a product 2. Agent B converts substrate 2 to product 3. Key components of our model are the common resources, which are substrates or products that serve in common among different types of agents. For example, in Fig. 1, resource 2 is a common resource because it is both a product of A and a reactant for B. Figs. 1 and 3 also show that if agents A and B come together by some process, then the AB complex is a "machine" that converts 1s to 3s, mediated by the intermediary resource 2s.
Agent B (Fig. 1) may take up a substrate molecule 2 from either of two sources: either the 2 was produced as the output from a nearby A agent, or the 2 was supplied externally from the environment, if 2s are available from external sources. Because we assume that Bs are Michaelis–Menten catalysts, a B will bind to its substrate, a 2 in this case. Bs will concentrate around 2s simply because Bs flow down their chemical potential gradients, in the same way that solutes in chromatographic mobile phases will seek out and bind to stationary-phase surfaces for which they have affinity.
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