生物多样性 ›› 2017, Vol. 25 ›› Issue (1): 94-106.DOI: 10.17520/biods.2016260

• • 上一篇    

遗传密码子的起源——从能量转化到信息化

谢平*   

  1. 中国科学院水生生物研究所, 武汉 430072
  • 收稿日期:2016-09-14 接受日期:2016-10-05 出版日期:2017-01-20 发布日期:2017-02-08
  • 通讯作者: 谢平

The origin of genetic codes: from energy transformation to informatiza- tion

Ping Xie   

  1. Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan 430072
  • Received:2016-09-14 Accepted:2016-10-05 Online:2017-01-20 Published:2017-02-08

摘要:

大自然将奥秘或法则隐匿于一套密码之中, 藉此创作出数以千万计的物种, 之后又将其销毁, 周而复始, 生生不息……虽然遗传密码子的破译已过去了半个多世纪, 但对它的起源人们依然一无所知, 有人甚至宣称这是不可知的, 还有一些人则认为它源自外来的设计。生命/遗传密码子的起源被誉为现代生命科学的最大谜团之一, 但它却关乎人们对生命本质与演化的认知。关于遗传密码子的起源, 已提出了各式各样的假说, 如凝固事件假说、立体化学假说、共进化假说、综合进化假说, 等等。但这些假说有两个致命缺陷: 首先, 没有哪一个能解释为何遗传密码子要如此演化; 其次, 都未从生化系统演化的视角来予以解释(部分与整体的关系)。近年, 虽然对密码子变异或可塑性及其与氨基酸分配的关系等研究很多, 但在密码子起源方面几乎没有取得实质性进展。本文从密码子与生化系统的内在关联之中探寻它们可能的协同演化机理, 认为遗传密码是原始细胞从能量转化到信息化演化过程的产物, 而三磷酸腺苷(ATP)扮演了最重要的角色。本文提出的“ATP中心假说”认为, ATP既是能量的载体, 也是信息的载体, 在核酸和蛋白质之间搭起了桥梁, 是遗传密码子出现的始作俑者: (a)ATP是光能转化成化学能的终端; (b)导演了一系列的生化循环(如卡尔文循环、糖酵解和三羧酸循环等)及令人眼花缭乱的元素重组; (c)它通过自身的转化与缩合将错综复杂的生命过程信息化——筛选出用4种碱基编码20多种氨基酸的三联体密码子系统(43 = 64, 还有相当大的编码冗余), 精巧地构建了一套遗传信息的保存、复制、转录和翻译以及多肽链的生产体系; (d)演绎出蛋白质与核酸互为因果的反馈体系, 并在个体生存的方向性筛选中, 构筑了对细胞内成百上千种同步发生的生化反应进行秩序化管控(自组织)的复杂体系与规则, 最终建立起个性生命的同质化传递机制——遗传。当然, 未来还需要更多的实验证据来验证这一假说。

关键词: 遗传密码的起源, ATP中心假说, 光合介导, 信息化, 结构化, 同质性个体

Abstract:

It is a miracle of nature that a set of genetic codes have assembled tens of millions of different species on the earth. However, no one knows exactly how these genetic codes came into being. Many biologists hold the pessimistic view that an exact reconstruction of the process of code construction may never be possible. It is even believed that the origin of the genetic code is unknowable, as there is no trace in physics or chemistry of the control of chemical reactions by a sequence of any sort or of a code between sequences. Many papers have been published with titles indicating that they explore the origin of the genetic code, but in actuality the content deals only with its evolution. More than half a century has passed since the discovery of genetic codes, but their origin is still one of the greatest mysteries in the modern life sciences. Are the genetic codons really unknowable? Do they require external design? So far, several hypotheses have been proposed to explain the origin of the genetic code, including the frozen accident hypothesis, stereochemical hypothesis, co-evolution hypothesis, and synthetic hypothesis. These hypotheses suffer from two fatal defects: first, none can explain satisfactorily why the genetic codes evolved, and second, none has explained the origin of genetic codes from that of the biochemical system (a relation of part to whole). In other words, all of these hypotheses completely overlooked the coevolution of genetic codes with the biochemical system. In recent decades, very little definitive progress has been made, although intensive studies have focused on variation or flexibility of the codes and possible rules of codon allocations to amino acids. This paper is aimed to explore the secrets of coevolution between the codon and the biochemical system. The genetic codes were likely an evolutionary product of primordial cells from energy transformation to informatization when ATP played a crucial role. Here, we present an ATP-centric hypothesis aimed at exploring the hidden primordial world inspiring the origin of genetic codes. We examined how and why ATP is at the heart of the extant biochemical system, and how the genetic codes came into being with the evolution of the biochemical system driven by photosynthesis. ATP, carriers of both energy and information, provide a bridge between amino acids and proteins, and are most likely the initiator of the genetic codes. In short, the energetic ATP together with its derivatives could randomly extend chains of both polynucleotides and polypeptides, which made it possible to establish or fix chemical relations between sequences of nucleotides in polynucleotides and amino acids in polypeptides from their numerous random combinations through a feedback mechanism (selection of cellular survival); and technically, photosynthesis, a goal-oriented process, enabled various biotic factors or reactions (ATP, lipid vesicle, informatization, structuralization, homogenous individual, individuality, survival, etc.) to be integrated into an operating system of genetic codes. It is challenging to crack the mystery of genetic codes, but sophisticated experimental evidence are needed in the future.

Key words: origin of genetic codes, ATP-centric hypothesis, photosynthesis-mediated, informatization, structuralization, homogenous individual