生物谷： 盡管科學(xué)家已經(jīng)知道,，生命出現(xiàn)在地球之前，必先有一些原始代謝機制,，或類似RNA復(fù)制機制的物體存在,。但究竟這些機制，一開始是如何產(chǎn)生的呢? 針對這問題,，兩位UCSF的科學(xué)家，提出了一個模型來說明,，簡單的化學(xué)及物理變化也許就足以構(gòu)成基礎(chǔ)的生命,。這份研究將發(fā)表在近期的PNAS期刊,。
Ken Dill博士說：此模型要闡述的基本觀念就是，酵素之間簡單的化學(xué)反應(yīng)是可以在微矩規(guī)模（micro scale）下的天擇過程中進行,。一般所謂的天擇過程是指，在不同生物體上隨機出現(xiàn)特征,，藉由競爭或合作留下最能適應(yīng)環(huán)境的條件,，接著該條件透過遺傳,，而出現(xiàn)在更多生命體。而這份研究中,，認為酵素間的化學(xué)反應(yīng),，也具有天擇般類似的過程: 例如競爭,，合作，創(chuàng)新,，及對穩(wěn)定的偏好,。
Dill稱這種過程叫做“隨機的創(chuàng)新”（random innovation），也就是隨機反應(yīng)并無意的創(chuàng)造出一個穩(wěn)定的復(fù)合物,。舉例來說,，兩個在溶液中具有不同催化功能的催化劑A及B，是有可能形成所謂的綜合體AB,。關(guān)鍵在于,，如果催化劑A能在反應(yīng)過程中，釋放出催化劑B所需使用到的成分,，且如果催化劑B周圍沒有其他物體能提供這樣的成分,，則催化劑A及B終究會聚在一起，而成為一種綜合AB,。藉由這例子,，可以顯示出為何一系列簡單的化學(xué)反應(yīng)，最后有可能形成一個巨大而復(fù)雜的分子結(jié)構(gòu),。
長久以來,，在生命起源的議題上，促成那些沒有自我意識的化學(xué)物,，組成精巧生化反應(yīng)的原因,，一直是一個謎。而如今,，這份研究,，提出了一個可能的答案，就是“天擇驅(qū)動了這個過程”,。 （援引華文生技網(wǎng)）
原始出處:
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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