PDF(Pubmed)
Abstract：
The RNA world hypothesis proposes that during the early evolution of life, primordial genomes of the first self-propagating evolutionary units existed in the form of RNA-like polymers. Autonomous, non-enzymatic, and sustained replication of such information carriers presents a problem, because product formation and hybridization between template and copy strands reduces replication speed. Kinetics of growth is then parabolic with the benefit of entailing competitive coexistence, thereby maintaining diversity. Here, we test the information-maintaining ability of parabolic growth in stochastic multispecies population models under the constraints of constant total population size and chemostat conditions. We find that large population sizes and small differences in the replication rates favor the stable coexistence of the vast majority of replicator species (\'genes\'), while the error threshold problem is alleviated relative to exponential amplification. In addition, sequence properties (GC content) and the strength of resource competition mediated by the rate of resource inflow determine the number of coexisting variants, suggesting that fluctuations in building block availability favored repeated cycles of exploration and exploitation. Stochastic parabolic growth could thus have played a pivotal role in preserving viable sequences generated by random abiotic synthesis and providing diverse genetic raw material to the early evolution of functional ribozymes.
All living things use molecules known as nucleic acids to store instructions on how to grow and maintain themselves and pass these instructions down to the next generation. However, it remains unclear how these systems may have evolved from simple molecules in the environment when life began over 3.6 billion years ago. One idea proposes that, before the first cells evolved, abiotic chemical processes gave rise to substantial building blocks of ribonucleic acids (or RNAs, for short). Over time, RNAs could have combined to form polymers of random sequences that started to copy themselves to make simple machines, only carrying the information required to make more of the same RNAs. Later on, these RNA molecules teamed up with proteins, fats and other molecules to make the first cells. When RNA replicates, the parent molecule is used as a template to assemble a new copy. While the new RNA molecule remains attached to its template it prevents the template being used to make more RNA. Therefore, it is thought that the speed at which a specific RNA machine copied itself may have varied in a pattern known as parabolic growth. Furthermore, when RNA replicates without the help of other biological molecules, the process is very prone to errors, which would have severely limited how much information the RNA machines were able to pass on to the next generation. Theoretical work suggested that under certain conditions, parabolic growth may favor the maintenance of a large amount of RNA sequence-coded information, but it is not clear if this is actually possible in nature. To address this question, Paczkó et al. developed mathematical models to investigate the effect of parabolic growth on the ability of RNA to replicate without other biological molecules. The models show that when large numbers of RNAs are present, small differences in how quickly different RNAs replicated favored the stable coexistence of different RNA sequences. Parabolic growth decreased the adverse effect of copying errors, allowing larger pieces of RNA to faithfully replicate themselves. This work suggests that parabolic growth may help to maintain different types of RNA (or similar replicating molecules) in a population and in turn, help new simple life forms to evolve. In the future, these findings may be used as a framework for laboratory experiments to better understand how early life forms may have evolved.
All living things use molecules known as nucleic acids to store instructions on how to grow and maintain themselves and pass these instructions down to the next generation. However, it remains unclear how these systems may have evolved from simple molecules in the environment when life began over 3.6 billion years ago. One idea proposes that, before the first cells evolved, abiotic chemical processes gave rise to substantial building blocks of ribonucleic acids (or RNAs, for short). Over time, RNAs could have combined to form polymers of random sequences that started to copy themselves to make simple machines, only carrying the information required to make more of the same RNAs. Later on, these RNA molecules teamed up with proteins, fats and other molecules to make the first cells. When RNA replicates, the parent molecule is used as a template to assemble a new copy. While the new RNA molecule remains attached to its template it prevents the template being used to make more RNA. Therefore, it is thought that the speed at which a specific RNA machine copied itself may have varied in a pattern known as parabolic growth. Furthermore, when RNA replicates without the help of other biological molecules, the process is very prone to errors, which would have severely limited how much information the RNA machines were able to pass on to the next generation. Theoretical work suggested that under certain conditions, parabolic growth may favor the maintenance of a large amount of RNA sequence-coded information, but it is not clear if this is actually possible in nature. To address this question, Paczkó et al. developed mathematical models to investigate the effect of parabolic growth on the ability of RNA to replicate without other biological molecules. The models show that when large numbers of RNAs are present, small differences in how quickly different RNAs replicated favored the stable coexistence of different RNA sequences. Parabolic growth decreased the adverse effect of copying errors, allowing larger pieces of RNA to faithfully replicate themselves. This work suggests that parabolic growth may help to maintain different types of RNA (or similar replicating molecules) in a population and in turn, help new simple life forms to evolve. In the future, these findings may be used as a framework for laboratory experiments to better understand how early life forms may have evolved.
摘要：
RNA世界假说提出，在生命的早期进化过程中，第一个自繁殖进化单元的原始基因组以RNA样聚合物的形式存在。自治,非酶，这种信息载体的持续复制提出了一个问题，因为模板和拷贝链之间的产物形成和杂交降低了复制速度。增长的动力学是抛物线的，具有竞争性共存的好处，从而保持多样性。这里,我们在总种群规模和恒化器条件不变的情况下，在随机多物种种群模型中测试抛物线生长的信息保持能力。我们发现，大的种群规模和复制率的小差异有利于绝大多数的复制物种（\'基因\'）的稳定共存，而误差阈值问题相对于指数放大有所缓解。此外,序列属性（GC含量）和资源流入率介导的资源竞争强度决定了共存变体的数量，这表明积木可用性的波动有利于重复的勘探和开发周期。因此，随机抛物线生长可能在保留由随机非生物合成产生的可行序列并为功能核酶的早期进化提供多种遗传原料方面发挥了关键作用。
所有生物都使用称为核酸的分子来存储有关如何生长和维持自身的指令，并将这些指令传递给下一代。然而,目前尚不清楚这些系统是如何从36亿年前生命开始的环境中的简单分子进化而来的。一个想法提出，在第一个细胞进化之前，非生物化学过程产生了大量的核糖核酸(或RNA，简称）。随着时间的推移,RNA可以结合形成随机序列的聚合物，这些聚合物开始自我复制以制造简单的机器，只携带制造更多相同RNA所需的信息。稍后，这些RNA分子与蛋白质结合在一起，脂肪和其他分子来制造第一个细胞。当RNA复制时，母体分子用作模板以组装新的拷贝。虽然新的RNA分子仍然附着在其模板上，但它阻止了模板被用来制造更多的RNA。因此,人们认为，特定RNA机器复制自身的速度可能以抛物线生长的模式变化。此外，当RNA在没有其他生物分子的帮助下复制时，这个过程很容易出错，这将严重限制RNA机器能够传递给下一代的信息。理论工作表明，在一定条件下，抛物线生长可能有利于维持大量RNA序列编码信息，但目前还不清楚这是否真的可能。为了解决这个问题，Paczkóetal.建立了数学模型来研究抛物线生长对RNA在没有其他生物分子的情况下复制能力的影响。模型显示，当大量的RNA存在时，不同RNA复制速度的微小差异有利于不同RNA序列的稳定共存。抛物线增长减少了复制错误的不利影响，允许较大的RNA片段忠实地自我复制。这项工作表明，抛物线生长可能有助于维持种群中不同类型的RNA（或类似的复制分子），帮助新的简单生命形式进化。在未来,这些发现可以用作实验室实验的框架，以更好地了解早期生命形式可能是如何进化的。
所有生物都使用称为核酸的分子来存储有关如何生长和维持自身的指令，并将这些指令传递给下一代。然而,目前尚不清楚这些系统是如何从36亿年前生命开始的环境中的简单分子进化而来的。一个想法提出，在第一个细胞进化之前，非生物化学过程产生了大量的核糖核酸(或RNA，简称）。随着时间的推移,RNA可以结合形成随机序列的聚合物，这些聚合物开始自我复制以制造简单的机器，只携带制造更多相同RNA所需的信息。稍后，这些RNA分子与蛋白质结合在一起，脂肪和其他分子来制造第一个细胞。当RNA复制时，母体分子用作模板以组装新的拷贝。虽然新的RNA分子仍然附着在其模板上，但它阻止了模板被用来制造更多的RNA。因此,人们认为，特定RNA机器复制自身的速度可能以抛物线生长的模式变化。此外，当RNA在没有其他生物分子的帮助下复制时，这个过程很容易出错，这将严重限制RNA机器能够传递给下一代的信息。理论工作表明，在一定条件下，抛物线生长可能有利于维持大量RNA序列编码信息，但目前还不清楚这是否真的可能。为了解决这个问题，Paczkóetal.建立了数学模型来研究抛物线生长对RNA在没有其他生物分子的情况下复制能力的影响。模型显示，当大量的RNA存在时，不同RNA复制速度的微小差异有利于不同RNA序列的稳定共存。抛物线增长减少了复制错误的不利影响，允许较大的RNA片段忠实地自我复制。这项工作表明，抛物线生长可能有助于维持种群中不同类型的RNA（或类似的复制分子），帮助新的简单生命形式进化。在未来,这些发现可以用作实验室实验的框架，以更好地了解早期生命形式可能是如何进化的。
