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文件:Difference DNA RNA-EN.svg
A comparison of RNA (left) with DNA (right), showing the helices and nucleobases each employs RNA(左)和DNA(右)的比较,显示了各自使用的螺旋和核碱基

The RNA world is a hypothetical stage in the evolutionary history of life on Earth, in which self-replicating RNA molecules proliferated before the evolution of DNA and proteins. The term also refers to the hypothesis that posits the existence of this stage.

RNA 世界是地球生命进化史中的一个假想阶段,在这个阶段中,自我复制的 RNA 分子在 DNA 和蛋白质进化之前就已经繁殖。这个术语也指假定存在这个阶段的假设。

[终译]RNA 世界是地球生命进化史中的一个假想阶段,在这个阶段中,自复制的 RNA 分子在 DNA 和蛋白质进化之前就已经增殖。这个术语也指假定存在这个阶段的假设。

Alexander Rich first proposed the concept of the RNA world in 1962,[1] and Walter Gilbert coined the term in 1986.[2] Alternative chemical paths to life have been proposed,[3] and RNA-based life may not have been the first life to exist.[2][4] Even so, the evidence for an RNA world is strong enough that the hypothesis has gained wide acceptance.[1][5][6] The concurrent formation of all four RNA building blocks further strengthened the hypothesis.[7]

亚历山大 · 里奇在1962年首次提出 RNA 世界的概念,沃尔特 · 吉尔伯特在1986年创造了这个术语。另一种通往生命的化学途径已经被提出,基于 rna 的生命可能并不是第一个存在的生命。即便如此,RNA 世界的证据足够强大,以至于这个假设已经被广泛接受。同时形成的所有四个 RNA 构建块进一步加强了假设。

[终译]亚历山大 · 里奇在1962年首次提出 RNA 世界的概念,沃尔特 · 吉尔伯特在1986年创造了这个术语。另一种通往生命的化学途径已经被提出——基于RNA 的生命可能并不是第一个存在的生命。即便如此,RNA 世界的证据足够有力,以至于这个假设已经被广泛接受。所有四种RNA构件的同时形成进一步加强了假设。

Like DNA, RNA can store and replicate genetic information; like protein enzymes, RNA enzymes (ribozymes) can catalyze (start or accelerate) chemical reactions that are critical for life.[8] One of the most critical components of cells, the ribosome, is composed primarily of RNA. Ribonucleotide moieties in many coenzymes, such as acetyl-CoA, NADH, FADH, and F420, may be surviving remnants of covalently bound coenzymes in an RNA world.[9]

像 DNA 一样,RNA 可以存储和复制遗传信息; 像蛋白质酶一样,RNA 酶(核酶)可以催化(启动或加速)对生命至关重要的化学反应。核糖体是细胞最重要的组成部分之一,主要由 RNA 组成。许多辅酶中的核苷酸部分,如乙酰辅酶 a、 NADH、 FADH 和 F420,可能是 RNA 世界中共价结合的辅酶的残余。

[终译]像 DNA 一样,RNA 可以存储和复制遗传信息;像蛋白质酶一样,RNA 酶(核酶)可以催化(启动或加速)对生命至关重要的化学反应。核糖体是细胞最重要的组成部分之一,主要由 RNA 组成。许多辅酶中的核苷酸部分,如乙酰辅酶 CoA、 NADH、 FADH 和 F420,可能是 RNA 世界中共价结合的辅酶的残余。

Although RNA is fragile, some ancient RNAs may have evolved the ability to methylate other RNAs to protect them.[10]

虽然 RNA 是脆弱的,一些古老的 RNA 可能已经进化出甲基化其他 RNA 来保护它们的能力。

[终译]尽管 RNA 是脆弱的,一些古老的 RNA 可能已经进化出甲基化其他 RNA 的能力来保护它们。

If the RNA world existed, it was probably followed by an age characterized by the evolution of ribonucleoproteins (RNP world),[2] which in turn ushered in the era of DNA and longer proteins. DNA has greater stability and durability than RNA; this may explain why it became the predominant information storage molecule.[11] Protein enzymes may have come to replace RNA-based ribozymes as biocatalysts because their greater abundance and diversity of monomers makes them more versatile. As some co-factors contain both nucleotide and amino-acid characteristics, it may be that amino acids, peptides and finally proteins initially were co-factors for ribozymes.[9]

如果 RNA 世界真的存在,那么随之而来的很可能是一个核糖核蛋白进化拥有属性的时代,这个时代又进入了 DNA 和更长的蛋白质时代。DNA 比 RNA 具有更高的稳定性和耐久性,这可以解释为什么它成为主要的信息存储分子。蛋白质酶作为生物催化剂可能已经取代了基于 rna 的核酶,因为其单体的丰富性和多样性使它们更加通用。由于某些辅助因子同时具有核苷酸和氨基酸的特性,可能氨基酸、多肽和最终蛋白质最初是核酶的辅助因子。

[终译]如果 RNA 世界真的存在,那么很可能伴随着一个以核糖核蛋白进化为特征的时代(RNA世界),这反过来又迎来了DNA和更长蛋白质的时代。DNA 比 RNA 具有更高的稳定性和持久性,这可以解释为什么它成为主要的信息存储分子。蛋白质酶作为生物催化剂可能已经取代了基于RNA的核酶,因为它们更丰富和多样的单体使它们更通用。由于某些辅助因子同时具有核苷酸和氨基酸的特征,可能氨基酸、多肽和蛋白质最初是核酶的辅助因子。

History

One of the challenges in studying abiogenesis is that the system of reproduction and metabolism utilized by all extant life involves three distinct types of interdependent macromolecules (DNA, RNA, and protein). This suggests that life could not have arisen in its current form, which has led researchers to hypothesize mechanisms whereby the current system might have arisen from a simpler precursor system.[12] American molecular biologist Alexander Rich was the first to posit a coherent hypothesis on the origin of nucleotides as precursors of life.[13] In an article he contributed to a volume issued in honor of Nobel-laureate physiologist Albert Szent-Györgyi, he explained that the primitive Earth's environment could have produced RNA molecules (polynucleotide monomers) that eventually acquired enzymatic and self-replicating functions.[14]

历史 = = 研究自然发生的挑战之一是,所有现存生命所利用的繁殖和代谢系统包括三种不同类型的相互依存的大分子(DNA、 RNA 和蛋白质)。这表明,生命不可能以目前的形式出现,这使研究人员假设,目前的系统可能是从一个更简单的前体系统中产生的。美国分子生物学家亚历山大 · 里奇是第一个提出关于核苷酸作为生命前体起源的连贯假说的人。在为纪念诺贝尔生理学奖获得者圣捷尔吉·阿尔伯特的一篇文章中,他解释说,原始的地球环境可能产生了 RNA 分子(多核苷酸单体) ,这些分子最终获得了酶和自我复制的功能。

[终译]研究自然发生的挑战之一是,所有现存生命所利用的繁殖和代谢系统包括三种不同类型的相互依存的大分子(DNA、 RNA 和蛋白质)。这表明,生命不可能以目前的形式出现,这使研究人员假设,目前的系统可能是从一个更简单的前体系统中产生的。美国分子生物学家亚历山大 · 里奇是第一个提出核苷酸是生命前体的通俗假说的人。在一篇为纪念诺贝尔生理学奖获得者圣捷尔吉·阿尔伯特(Albert Szent-Györgyi)的文章中,他解释说,原始的地球环境可能产生了 RNA 分子(多核苷酸单体) ,这些分子最终获得了酶和自复制功能。

Further concept of RNA as a primordial molecule can be found in papers by Francis Crick[15] and Leslie Orgel,[16] as well as in Carl Woese's 1967 book The Genetic Code.[17]Hans Kuhn in 1972 laid out a possible process by which the modern genetic system might have arisen from a nucleotide-based precursor, and this led Harold White in 1976 to observe that many of the cofactors essential for enzymatic function are either nucleotides or could have been derived from nucleotides. He proposed a scenario whereby the critical electrochemistry of enzymatic reactions would have necessitated retention of the specific nucleotide moieties of the original RNA-based enzymes carrying out the reactions, while the remaining structural elements of the enzymes were gradually replaced by protein, until all that remained of the original RNAs were these nucleotide cofactors, "fossils of nucleic acid enzymes".[18] The phrase "RNA World" was first used by Nobel laureate Walter Gilbert in 1986, in a commentary on how recent observations of the catalytic properties of various forms of RNA fit with this hypothesis.[19]

在弗朗西斯•克里克(Francis Crick)和莱斯利•奥格尔(Leslie Orgel)的论文中,以及卡尔•沃斯(Carl Woese)1967年出版的《遗传密码》(The Genetic Code)一书中,都可以找到 RNA 作为一种原始分子的进一步概念。西班牙语。(1967).遗传密码: 遗传表达的分子基础。3月186日。Harper & RowHans Kuhn 在1972年提出了一个可能的过程,通过这个过程,现代遗传系统可能产生于以核苷酸为基础的前体,这导致 Harold White 在1976年观察到,许多辅助因子对酶的功能至关重要,要么是核苷酸,要么可能是从核苷酸衍生而来。他提出了一种假设,即酶反应的关键电化学是必须保留原始 rna 酶进行反应的特定核苷酸序列,而酶的其余结构元素逐渐被蛋白质取代,直到原始 rna 剩下的全部都是这些核苷酸辅助因子,即“核酸酶的化石”。1986年,诺贝尔奖获得者沃尔特 · 吉尔伯特首次使用了“ RNA 世界”这个短语,他在一篇评论文章中阐述了最近对各种形式的 RNA 催化特性的观察是如何与这一假设相吻合的。

[终译]在弗朗西斯•克里克(Francis Crick)和莱斯利•奥格尔(Leslie Orgel)的论文中,以及卡尔•沃斯(Carl Woese)1967年出版的《遗传密码》(The Genetic Code)一书中,都可以找到 RNA 是原始分子的进一步概念。Harper和RowHans Kuhn 在1972年提出了一种可能的过程,通过这个过程,现代遗传系统可能产生于以核苷酸为基础的前体,这导致 Harold White 在1976年观察到,许多辅助因子对酶的功能至关重要,要么是核苷酸,要么可能是从核苷酸衍生而来。他提出了一种方案,即酶反应的临界电化学必须保留进行反应的原始RNA基酶的特定核苷酸部分,而酶的其余结构元件逐渐被蛋白质取代,直到原始RNA剩下的全部都是这些核苷酸辅助因子,即“核酸酶的化石”。1986年,诺贝尔奖获得者沃尔特 · 吉尔伯特首次使用了“RNA 世界”这个短语,他在一篇综述文章中阐述了最近对各种形式的 RNA 催化特性的观察是如何与这一假设相吻合的。

Properties of RNA

The properties of RNA make the idea of the RNA world hypothesis conceptually plausible, though its general acceptance as an explanation for the origin of life requires further evidence.[20] RNA is known to form efficient catalysts and its similarity to DNA makes clear its ability to store information. Opinions differ, however, as to whether RNA constituted the first autonomous self-replicating system or was a derivative of a still-earlier system.[2] One version of the hypothesis is that a different type of nucleic acid, termed pre-RNA, was the first one to emerge as a self-reproducing molecule, to be replaced by RNA only later. On the other hand, the discovery in 2009 that activated pyrimidine ribonucleotides can be synthesized under plausible prebiotic conditions[21] suggests that it is premature to dismiss the RNA-first scenarios.[2] Suggestions for 'simple' pre-RNA nucleic acids have included peptide nucleic acid (PNA), threose nucleic acid (TNA) or glycol nucleic acid (GNA).[22][23] Despite their structural simplicity and possession of properties comparable with RNA, the chemically plausible generation of "simpler" nucleic acids under prebiotic conditions has yet to be demonstrated.[24]

从 RNA 的性质来看,RNA世界学说理论在概念上是可信的,尽管它被普遍接受为生命起源的解释还需要进一步的证据。众所周知,RNA 能够形成有效的催化剂,而且它与 DNA 的相似性清楚地表明了它存储信息的能力。然而,对于 RNA 是否构成第一个自主自我复制系统或者是一个更早的系统的衍生物,人们的看法不一。这个假说的一个版本是,一种不同类型的核酸,称为前 RNA,是第一个作为自我繁殖分子出现的,后来被 RNA 所取代。另一方面,2009年发现活化的嘧啶核苷酸可以在合理的前生命条件下合成,这表明现在排除 rna 优先的假设还为时过早。关于简单的前 rna 核酸的建议包括肽核酸(PNA)、苏糖核酸(TNA)或 GNA (GNA)。尽管它们的结构简单而且具有与 RNA 相似的特性,但是在生命起源之前的条件下,化学上似乎可能产生的“更简单的”核酸尚未得到证实。

[终译]从 RNA 的性质来看,RNA世界假说在概念上是可信的,尽管它被普遍接受为生命起源的解释还需要进一步的证据。众所周知,RNA 能够形成有效的催化剂,而且它与 DNA 的相似性清楚地表明了它存储信息的能力。然而,关于RNA是第一个自主自我复制系统,还是更早系统的衍生物,人们的看法不一。该假说的一个版本是,一种不同类型的核酸,称为前 RNA,是第一个作为自复制分子出现的核酸,只是后来被RNA取代。另一方面,2009年发现活化的嘧啶核糖核苷酸可以在合理的前生命条件下合成,这表明现在排除RNA优先的假设还为时过早。关于简单的前RNA核酸的建议包括肽核酸(PNA)、苏糖核酸(TNA)或乙二醇核酸(GNA)。尽管它们的结构简单,并具有与RNA相当的性质,但化学上看似合理的“更简单”的核酸在生命起源前的条件下仍有待证明。

RNA as an enzyme

模板:Further

RNA enzymes, or ribozymes, are found in today's DNA-based life and could be examples of living fossils. Ribozymes play vital roles, such as that of the ribosome. The large subunit of the ribosome includes an rRNA responsible for the peptide bond-forming peptidyl transferase activity of protein synthesis. Many other ribozyme activities exist; for example, the hammerhead ribozyme performs self-cleavage[25] and an RNA polymerase ribozyme can synthesize a short RNA strand from a primed RNA template.[26]

RNA 酶,或称核酶,存在于今天的 dna 生命中,可能是活化石的例子。核酶起着至关重要的作用,例如核糖体。核糖体的大亚基包括一个 rRNA,负责蛋白质合成中形成肽键的肽基转移酶活性。许多其他的核酶活性也存在; 例如,锤头状核酶可以进行自我切割,而 RNA 聚合酶核酶可以从已引物的 RNA 模板合成短的 RNA 链。

[终译]RNA 酶,或称核酶,在今天基于DNA的生命中被发现,可能是活化石的例子。核酶起着至关重要的作用,例如核糖体。核糖体的大亚基包括一个 rRNA,负责蛋白质合成中形成肽键的肽基转移酶活性。许多其他的核酶活性也存在;例如,锤头状核酶可以进行自我切割,而 RNA 聚合酶核酶可以从引发的 RNA 模板合成短的 RNA 链。

Among the enzymatic properties important for the beginning of life are:

Self-replication
The ability to self-replicate, or synthesize other RNA molecules; relatively short RNA molecules that can synthesize others have been artificially produced in the lab. The shortest was 165 bases long, though it has been estimated that only part of the molecule was crucial for this function. One version, 189 bases long, had an error rate of just 1.1% per nucleotide when synthesizing an 11 nucleotide long RNA strand from primed template strands.[27] This 189 base pair ribozyme could polymerize a template of at most 14 nucleotides in length, which is too short for self replication, but is a potential lead for further investigation. The longest primer extension performed by a ribozyme polymerase was 20 bases.[28] In 2016, researchers reported the use of in vitro evolution to improve dramatically the activity and generality of an RNA polymerase ribozyme by selecting variants that can synthesize functional RNA molecules from an RNA template. Each RNA polymerase ribozyme was engineered to remain linked to its new, synthesized RNA strand; this allowed the team to isolate successful polymerases. The isolated RNA polymerases were again used for another round of evolution. After several rounds of evolution, they obtained one RNA polymerase ribozyme called 24-3 that was able to copy almost any other RNA, from small catalysts to long RNA-based enzymes. Particular RNAs were amplified up to 10,000 times, a first RNA version of the polymerase chain reaction (PCR).[29]
Catalysis
The ability to catalyze simple chemical reactions—which would enhance creation of molecules that are building blocks of RNA molecules (i.e., a strand of RNA that would make creating more strands of RNA easier). Relatively short RNA molecules with such abilities have been artificially formed in the lab.[30][31] A recent study showed that almost any nucleic acid can evolve into a catalytic sequence under appropriate selection. For instance, an arbitrarily chosen 50-nucleotide DNA fragment encoding for the Bos taurus (cattle) albumin mRNA was subjected to test-tube evolution to derive a catalytic DNA (Deoxyribozyme, also called DNAzyme) with RNA-cleavage activity. After only a few weeks, a DNAzyme with significant catalytic activity had evolved.[32] In general, DNA is much more chemically inert than RNA and hence much more resistant to obtaining catalytic properties. If in vitro evolution works for DNA it will happen much more easily with RNA.
Amino acid-RNA ligation
The ability to conjugate an amino acid to the 3'-end of an RNA in order to use its chemical groups or provide a long-branched aliphatic side-chain.[33]
Peptide bond formation
The ability to catalyse the formation of peptide bonds between amino acids to produce short peptides or longer proteins. This is done in modern cells by ribosomes, a complex of several RNA molecules known as rRNA together with many proteins. The rRNA molecules are thought responsible for its enzymatic activity, as no amino-acid residues lie within 18Å of the enzyme's active site,[20] and, when the majority of the amino-acid residues in the ribosome were stringently removed, the resulting ribosome retained its full peptidyl transferase activity, fully able to catalyze the formation of peptide bonds between amino acids.[34] A much shorter RNA molecule has been synthesized in the laboratory with the ability to form peptide bonds, and it has been suggested that rRNA has evolved from a similar molecule.[35] It has also been suggested that amino acids may have initially been involved with RNA molecules as cofactors enhancing or diversifying their enzymatic capabilities, before evolving into more complex peptides. Similarly, tRNA is suggested to have evolved from RNA molecules that began to catalyze amino acid transfer.[36]

生命起源的重要酶特性包括:自我复制: 自我复制或合成其他 RNA 分子的能力; 在实验室人工合成的相对较短的 RNA 分子,可以合成其他 RNA 分子。最短的是165个碱基的长度,尽管据估计只有一部分分子对这个功能起关键作用。其中一个版本有189个碱基长,当从引物模板链合成11个核苷酸长的 RNA 链时,每个核苷酸的错误率只有1.1% 。这个189碱基对核酶可以使最多14个核苷酸的模板聚合,这对于自我复制来说太短了,但是有可能成为进一步研究的前沿。核酶聚合酶最长的引物延伸是20个碱基。Hanis.Zaher 和 peterj.Unrau,改进的延伸性和保真性更好的 RNA 聚合酶核酶的筛选。RNA (2007) ,13:1017-10262016年,研究人员报道了利用体外进化技术,通过从 RNA 模板中选择能合成功能性 RNA 分子的变体,显著提高 RNA 聚合酶的活性和通用性。每个 RNA 聚合酶核酶都被设计成与其新合成的 RNA 链连接,这使得研究小组能够分离出成功的聚合酶。分离的 RNA 聚合酶再次被用于另一轮进化。经过几轮的进化,他们获得了一种称为24-3的 RNA 聚合酶,这种酶能够复制几乎所有其他的 RNA,从小型催化剂到长 RNA 酶。特定的 RNA 被放大了10,000倍,这是聚合酶链式反应的第一个 RNA 版本。催化作用: 催化简单化学反应的能力ーー这种能力可以促进构成 RNA 分子基础的分子的产生(例如,一条 RNA 链可以更容易地产生更多的 RNA 链)。具有这种能力的相对较短的 RNA 分子已在实验室中人工形成。最近的一项研究表明,在适当的选择下,几乎任何核酸都能进化成催化序列。例如,任意选择牛白蛋白 mRNA 的50个核苷酸 DNA 片段经过试管进化,得到具有 rna 切割活性的催化 DNA (脱氧核酶,又称 DNA 酶)。仅仅几个星期之后,一种具有显著催化活性的脱氧核酶就产生了。一般来说,DNA 比 RNA 更具化学惰性,因此更难获得催化性能。如果体外进化适用于 DNA,那么 RNA 就更容易进化。氨基酸-RNA 连接: RNA 的3’端与氨基酸偶联的能力,以利用其化学基团或提供长支链脂肪族侧链。肽键形成: 催化氨基酸之间形成肽键以产生短肽或长肽的能力。在现代细胞中,这是通过核糖体完成的,核糖体是由几个 RNA 分子和许多蛋白质组成的复合体。核糖核酸分子被认为是负责其酶活性的,因为没有氨基酸残基位于酶的活性位点的18 ° 内,而且,当核糖体中的大部分氨基酸残基被严格地去除时,产生的核糖体保留了其完全的肽基转移酶活性,完全能够催化氨基酸之间的肽键的形成。在实验室中,人们已经合成了一种更短的 RNA 分子,它能够形成肽键,并且有人认为 RNA 是从一种类似的分子演化而来的。还有人认为,氨基酸可能最初与 RNA 分子有关,作为辅助因子增强或使其酶促能力多样化,然后演变成更复杂的多肽。类似地,tRNA 被认为是从催化氨基酸转移的 RNA 分子进化而来的。

[终译]

生命起源的重要酶特性包括:

自复制

自复制或合成其他 RNA 分子的能力;可以合成其他RNA的相对较短的RNA分子已经在实验室中人工制造出来了。最短的有165个碱基长,尽管据估计只有一部分分子对这个功能起关键作用。其中一个版本有189个碱基长,当从引物模板链合成11个核苷酸长的 RNA 链时,每个核苷酸的错误率只有1.1% 。这种189个碱基对的核酶可以使最多14个核苷酸的模板聚合,这对于自复制来说太短了,但是有可能成为进一步研究的前沿。核酶聚合酶进行的最长引物延伸是20个碱基。2016年,研究人员报道了利用体外进化技术,通过从 RNA 模板中选择能合成功能性 RNA 分子的变体,显著提高了 RNA 聚合酶的活性和通用性。每种RNA 聚合酶核酶都被设计成与其新合成的 RNA 链连接,这使得研究小组能够成功分离出聚合酶。分离的 RNA 聚合酶再次被用于另一轮进化。经过几轮进化,他们获得了一种称为24-3的 RNA 聚合酶,这种酶能够复制几乎任何其他RNA——从小型催化剂到长RNA酶。特定的 RNA 被放大了10,000倍,这是聚合酶链式反应(PCR)的第一个RNA版本。

催化作用

催化简单化学反应的能力ーー这将增强作为RNA分子构建模块的分子的创建(即一条 RNA 链可以更容易地创建更多的 RNA 链)。具有这种能力的相对较短的 RNA 分子已在实验室中人工形成。最近的一项研究表明,在适当的选择下,几乎任何核酸都能进化成催化序列。例如,任意选择编码牛白蛋白 mRNA 的50个核苷酸 的DNA 片段进行试管进化,得到具有RNA切割活性的催化DNA(脱氧核酶,又称 DNA 酶)。仅仅几个星期之后,一种具有显著催化活性的脱氧核酶就进化出来了。一般来说,DNA 比 RNA 更具化学惰性,因此更难获得催化性能。如果体外进化适用于 DNA,那么 它将更容易适用于RNA。

氨基酸-RNA连接

RNA 的3’端与氨基酸偶联的能力,以利用其化学基团或提供长支链脂肪族侧链。

肽键形成

催化氨基酸间形成肽键以产生短肽或更长蛋白质的能力。在现代细胞中,这是由核糖体完成的,核糖体是由几个称为rRNA的RNA分子和许多蛋白质组成的复合体。rRNA分子被认为是负责其酶活性的,因为没有氨基酸残基位于酶的活性位点的18° 范围内,而且,当核糖体中的大部分氨基酸残基被严格地去除时,产生的核糖体保留了其完整的肽基转移酶活性,完全能够催化氨基酸之间肽键的形成。在实验室中,人们已经合成了一种更短的 RNA 分子,它能够形成肽键,并且有人认为 rRNA 是从一种类似的分子演化而来的。还有人认为,在进化成更复杂的肽之前,氨基酸最初可能作为辅助因子参与RNA分子,增强或丰富它们的酶促能力。类似地,tRNA 被认为是从催化氨基酸转移的 RNA 分子进化而来的。

RNA in information storage ==信息存储中的RNA==

RNA is a very similar molecule to DNA, with only two major chemical differences (the backbone of RNA uses ribose instead of deoxyribose and its nucleobases include uracil instead of thymine). The overall structure of RNA and DNA are immensely similar—one strand of DNA and one of RNA can bind to form a double helical structure. This makes the storage of information in RNA possible in a very similar way to the storage of information in DNA. However, RNA is less stable, being more prone to hydrolysis due to the presence of a hydroxyl group at the ribose 2' position.

信息存储中的 RNA 是与 DNA 非常相似的分子,只有两个主要的化学差异(RNA 的骨架使用核糖代替脱氧核糖,其核酸酶包括尿嘧啶代替胸腺嘧啶)。RNA 和 DNA 的整体结构极为相似,一个 DNA 链和一个 RNA 链可以结合形成双螺旋结构。这使得在 RNA 中存储信息成为可能,就像在 DNA 中存储信息一样。然而,RNA 不太稳定,由于在核糖2’位置存在羟基,更容易水解。

[终译]RNA是与DNA非常相似的分子,只有两个主要的化学差异(RNA 的骨架使用核糖而不是脱氧核糖,其核酸酶包括尿嘧啶而不是胸腺嘧啶)。RNA 和 DNA 的整体结构极为相似,一个 DNA 链和一个 RNA 链可以结合形成双螺旋结构。这使得在 RNA 中存储信息成为可能,就像在 DNA 中存储信息一样。然而,RNA 不太稳定,由于在核糖2’位置存在羟基,更容易水解。

文件:Ribonucleic acid chemical structure.svg
The major difference between RNA and DNA is the presence of a hydroxyl group at the 2'-position. RNA和DNA的主要区别是在2 '位是否有一个羟基。

Comparison of DNA and RNA structure

The major difference between RNA and DNA is the presence of a hydroxyl group at the 2'-position of the ribose sugar in RNA (illustration, right).[20] This group makes the molecule less stable because, when not constrained in a double helix, the 2' hydroxyl can chemically attack the adjacent phosphodiester bond to cleave the phosphodiester backbone. The hydroxyl group also forces the ribose into the C3'-endo sugar conformation unlike the C2'-endo conformation of the deoxyribose sugar in DNA. This forces an RNA double helix to change from a B-DNA structure to one more closely resembling A-DNA.

RNA 和 DNA 之间的主要区别是在 RNA 中核糖糖的2’位置存在羟基(图右)。这个基团使得分子更不稳定,因为当不受双螺旋约束时,2’羟基可以化学攻击相邻的磷酸二酯键,切断磷酸二酯的主链。羟基还迫使核糖进入 C3’-endo 糖构象,不同于 DNA 中脱氧核糖的 C2’-endo 构象。这迫使 RNA 双螺旋从 B-DNA 结构转变为更接近 A-DNA 的结构。

[终译]RNA 和 DNA 之间的主要区别在于 RNA 中核糖的2’位置存在羟基(右图)。该基团使分子不太稳定,因为当不被限制在双螺旋中时,2’羟基可以化学攻击相邻的磷酸二酯键,从而裂解磷酸二酯的主链。羟基也迫使核糖形成C3’-内糖构象,这与DNA中脱氧核糖的C2’内糖构象不同。这迫使一个RNA双螺旋从B-DNA结构变成一个更像A-DNA的结构。

RNA also uses a different set of bases than DNA—adenine, guanine, cytosine and uracil, instead of adenine, guanine, cytosine and thymine. Chemically, uracil is similar to thymine, differing only by a methyl group, and its production requires less energy.[37] In terms of base pairing, this has no effect. Adenine readily binds uracil or thymine. Uracil is, however, one product of damage to cytosine that makes RNA particularly susceptible to mutations that can replace a GC base pair with a GU (wobble) or AU base pair.

RNA 还使用与 dna 不同的一组碱基ー腺嘌呤、鸟嘌呤、胞嘧啶和尿嘧啶,而不是腺嘌呤、鸟嘌呤、胞嘧啶和胸腺嘧啶。尿嘧啶在化学性质上与胸腺嘧啶相似,只是不同于甲基,而且它的产生需要更少的能量。在碱基配对方面,这没有影响。Adenine 容易与尿嘧啶或胸腺嘧啶结合。然而,尿嘧啶是胞嘧啶损伤的产物,使 RNA 特别容易受到突变的影响,这些突变可以用 GU (摆动)或 AU 碱基对替代 GC 碱基对。

[终译]RNA 还使用与DNA不同的一组碱基——腺嘌呤、鸟嘌呤、胞嘧啶和尿嘧啶,而不是腺嘌呤、鸟嘌呤、胞嘧啶和胸腺嘧啶。在化学上,尿嘧啶与胸腺嘧啶相似,只是有一个甲基不同,它的生产需要较少的能量。就碱基配对而言,这没有影响。腺嘌呤容易结合尿嘧啶或胸腺嘧啶。然而,尿嘧啶是胞嘧啶受损的一种产物,使得RNA特别容易发生突变,可以用GU(摇摆)或AU碱基对取代GC碱基对。

RNA is thought to have preceded DNA, because of their ordering in the biosynthetic pathways. The deoxyribonucleotides used to make DNA are made from ribonucleotides, the building blocks of RNA, by removing the 2'-hydroxyl group. As a consequence a cell must have the ability to make RNA before it can make DNA.

由于 RNA 在生物合成途径中的有序性,人们认为 RNA 先于 DNA。用于制造 DNA 的脱氧核糖核苷酸是由核糖核酸(RNA 的构建单元)通过去除2’-羟基而制成的。因此,细胞必须具备制造 RNA 的能力,才能制造 DNA。

[终译]由于 RNA 在生物合成途径中的有序性,人们认为 RNA 先于 DNA。用于制造 DNA 的脱氧核糖核苷酸是由核糖核酸(RNA 的构建单元)通过去除2’羟基而制成的。因此,细胞必须具备制造 RNA 的能力,才能制造 DNA。

Limitations of information storage in RNA

The chemical properties of RNA make large RNA molecules inherently fragile, and they can easily be broken down into their constituent nucleotides through hydrolysis.[38][39] These limitations do not make use of RNA as an information storage system impossible, simply energy intensive (to repair or replace damaged RNA molecules) and prone to mutation. While this makes it unsuitable for current 'DNA optimised' life, it may have been acceptable for more primitive life.

在 RNA 中信息存储的局限性 RNA 的化学特性使大的 RNA 分子内在地脆弱,它们可以通过水解很容易地分解成它们的组成核苷酸。这些限制并不意味着 RNA 作为一种信息存储系统是不可能的,只是能量密集型(修复或替换受损的 RNA 分子)和容易发生突变。虽然这使得它不适合目前的“ DNA 优化”生命,但对于更原始的生命来说,它可能是可以接受的。

[终译]RNA的化学性质使得大的RNA分子天生脆弱,它们可以通过水解很容易地被分解成它们的组成核苷酸。这些限制并不意味着 RNA 作为一种信息存储系统是不可能的,只是能量密集(修复或替换受损的 RNA 分子)和容易发生突变。虽然这使得它不适合目前的“ DNA 优化”生命,但对于更原始的生命来说,它可能是可以接受的。

RNA as a regulator

Riboswitches have been found to act as regulators of gene expression, particularly in bacteria, but also in plants and archaea. Riboswitches alter their secondary structure in response to the binding of a metabolite. This change in structure can result in the formation or disruption of a terminator, truncating or permitting transcription respectively.[40] Alternatively, riboswitches may bind or occlude the Shine–Dalgarno sequence, affecting translation.[41] It has been suggested that these originated in an RNA-based world.[42] In addition, RNA thermometers regulate gene expression in response to temperature changes.[43]

核糖开关已被发现作为基因表达的调节器,特别是在细菌中,但也在植物和古细菌中。核糖开关随着代谢产物的结合而改变其二级结构。这种结构上的改变可以导致终止子的形成或中断,分别截断或允许转录。或者,核糖开关可能束缚或封闭 Shine-Dalgarno 序列,影响翻译。有人认为,这些起源于一个基于 rna 的世界。此外,RNA 温度计根据温度变化调节基因表达。

[终译]核糖开关已被发现作为基因表达的调节器,特别是在细菌中,但也在植物和古菌中。核糖开关响应代谢产物的结合而改变其二级结构。这种结构上的改变可以导致终止子的形成或破坏,分别截断或允许转录。或者,核糖开关可能结合或封闭Shine-Dalgarno序列,影响翻译。有人认为,这些起源于一个基于RNA的世界。此外,RNA 温度计根据温度变化调节基因表达。

Support and difficulties ==支持和困难 = =

The RNA world hypothesis is supported by RNA's ability both to store, transmit, and duplicate genetic information, as DNA does, and to perform enzymatic reactions, like protein-based enzymes. Because it can carry out the types of tasks now performed by proteins and DNA, RNA is believed to have once been capable of supporting independent life on its own.[20] Some viruses use RNA as their genetic material, rather than DNA.[44] Further, while nucleotides were not found in experiments based on Miller-Urey experiment, their formation in prebiotically plausible conditions was reported in 2009;[21] a purine base, adenine, is merely a pentamer of hydrogen cyanide. Experiments with basic ribozymes, like Bacteriophage Qβ RNA, have shown that simple self-replicating RNA structures can withstand even strong selective pressures (e.g., opposite-chirality chain terminators).[45]

支持和困难 = RNA世界学说的支持是由 RNA 的能力,既存储,传输和复制遗传信息,如 DNA,并执行酶的反应,如蛋白质为基础的酶。由于 RNA 可以执行现在由蛋白质和 DNA 执行的任务,因此人们认为 RNA 曾经能够独立生存。一些病毒使用 RNA 作为它们的遗传物质,而不是 DNA.Patton,John t. 杂志编辑(2008)。分节型双链 RNA 病毒: 结构与分子生物学。凯斯特学术出版社。编辑单位: 传染病实验室,NIAID,NIH,Bethesda,MD 20892-8026。此外,虽然在基于米勒-尤列实验的实验中没有发现核苷酸,但在2009年报道了它们在预生物条件下形成的可能性; 嘌呤碱基腺嘌呤仅仅是氰化氢的五聚体。基本核酶的实验,如 Qβ噬菌体 RNA,表明简单的自我复制 RNA 结构可以承受甚至强大的选择压力(例如,反手性链终止器)。贝尔,格雷厄姆: 选择的基础。斯普林格,1997。

[终译]RNA能够像DNA一样储存、传递和复制遗传信息,并像基于蛋白质的酶一样进行酶促反应,这支持了RNA世界假说。由于RNA 可以执行现在由蛋白质和DNA执行的任务类型,RNA被认为曾经能够独自支持独立的生命。一些病毒使用RNA作为它们的遗传物质,而不是DNA。此外,虽然在基于米勒-尤列实验的实验中没有发现核苷酸,但在2009年报道了它们在生物起源前似乎合理的条件下的形成;嘌呤碱基腺嘌呤仅仅是氰化氢的五聚体。对基本核酶(如噬菌体Qβ RNA)的实验表明,简单的自复制RNA结构甚至可以承受强大的选择压力(例如,反手性链终止子)。

Since there were no known chemical pathways for the abiogenic synthesis of nucleotides from pyrimidine nucleobases cytosine and uracil under prebiotic conditions, it is thought by some that nucleic acids did not contain these nucleobases seen in life's nucleic acids.[46] The nucleoside cytosine has a half-life in isolation of 19 days at 模板:Convert and 17,000 years in freezing water, which some argue is too short on the geologic time scale for accumulation.[47] Others have questioned whether ribose and other backbone sugars could be stable enough to be found in the original genetic material,[48] and have raised the issue that all ribose molecules would have had to be the same enantiomer, as any nucleotide of the wrong chirality acts as a chain terminator.[49]

由于在生命起源前条件下,嘧啶核苷酸胞嘧啶和尿嘧啶的无机合成核苷酸没有已知的化学途径,一些人认为核酸不包含生命核酸中的这些核苷酸。核苷类胞嘧啶在冷冻水中的半衰期分别为19天和17,000年,有些人认为冷冻水中的地质年代太短,无法积累。其他人质疑核糖和其他骨架糖是否稳定到足以在原始遗传物质中被发现,并提出了所有核糖分子必须是相同的对映体的问题,因为任何错误的核苷酸的手性作为链终止剂。

[终译]由于在前生命起源条件下,从嘧啶核苷酸胞嘧啶和尿嘧啶无机合成核苷酸没有已知的化学途径,一些人认为核酸不包含生命核酸中的这些核苷酸。胞嘧啶核苷在冷冻水中的半衰期分别为19天和17,000年,有些人认为这在地质时间尺度上对于积累来说太短了。其他人质疑核糖和其他主链糖是否稳定到足以在原始遗传物质中被发现,并提出了所有核糖分子必须是相同的对映体的问题,因为任何错误的核苷酸的手性都可以充当链终止子。

Pyrimidine ribonucleosides and their respective nucleotides have been prebiotically synthesised by a sequence of reactions that by-pass free sugars and assemble in a stepwise fashion by including nitrogenous and oxygenous chemistries. In a series of publications, John Sutherland and his team at the School of Chemistry, University of Manchester, have demonstrated high yielding routes to cytidine and uridine ribonucleotides built from small 2- and 3-carbon fragments such as glycolaldehyde, glyceraldehyde or glyceraldehyde-3-phosphate, cyanamide, and cyanoacetylene. One of the steps in this sequence allows the isolation of enantiopure ribose aminooxazoline if the enantiomeric excess of glyceraldehyde is 60% or greater, of possible interest toward biological homochirality.[50] This can be viewed as a prebiotic purification step, where the said compound spontaneously crystallised out from a mixture of the other pentose aminooxazolines. Aminooxazolines can react with cyanoacetylene in a mild and highly efficient manner, controlled by inorganic phosphate, to give the cytidine ribonucleotides. Photoanomerization with UV light allows for inversion about the 1' anomeric centre to give the correct beta stereochemistry; one problem with this chemistry is the selective phosphorylation of alpha-cytidine at the 2' position.[51] However, in 2009, they showed that the same simple building blocks allow access, via phosphate controlled nucleobase elaboration, to 2',3'-cyclic pyrimidine nucleotides directly, which are known to be able to polymerise into RNA.[21] Organic chemist Donna Blackmond described this finding as "strong evidence" in favour of the RNA world.[52] However, John Sutherland said that while his team's work suggests that nucleic acids played an early and central role in the origin of life, it did not necessarily support the RNA world hypothesis in the strict sense, which he described as a "restrictive, hypothetical arrangement".[53]

嘧啶核苷及其核苷酸是通过一系列绕过游离糖的反应进行预生物合成的,包括含氮和含氧化学反应。在一系列出版物中,曼彻斯特大学化学学院的约翰 · 萨瑟兰和他的团队展示了由2-和3-碳小片段如乙醇醛、甘油醛或3- 磷酸甘油醛、氰胺和氰乙炔构成的胞苷和尿苷核苷的高产路线。如果甘油醛的对映体过量百分数大于或等于60% ,则该序列中的一个步骤允许拆分对映体核糖氨基噁唑啉,这可能对生物同手性有意义。返回文章页面【应用化学(期刊)】核苷前体的直接组装译者:。这可以看作是生命前的纯化步骤,该化合物自发地从其他戊糖氨基恶唑啉的混合物中结晶出来。在无机磷酸盐的控制下,氨基恶唑啉能与氰乙炔温和高效地反应生成胞苷核糖核苷。利用紫外光进行光反耦合可以在1’端反转,从而得到正确的 β 立体化学反应; 这种化学反应的一个问题是 α-胞苷在2’端的选择性磷酸化。然而,在2009年,他们展示了相同的简单构建模块,通过磷酸盐控制的核苷酸精化,可以直接进入2’,3’-环嘧啶核苷酸,这些已知能够聚合成 RNA。有机化学家唐娜 · 布莱克蒙德将这一发现描述为 RNA 世界的“有力证据”。然而,John Sutherland 说,虽然他的团队的工作表明核酸在生命起源的早期扮演了核心的角色,但是它并不一定支持严格意义上的 RNA世界学说,他将其描述为一种“限制性的,假设性的安排”。

[终译]嘧啶核糖核苷及其核苷酸是通过一系列绕过游离糖的反应,并通过包括含氮和含氧的化学物质以逐步的方式组装,在生命之前被合成。在一系列出版物中,曼彻斯特大学化学学院的约翰 · 萨瑟兰(John Sutherland)和他的团队展示了从小的2-和3-碳片段如乙醇醛、甘油醛或甘油醛-3-磷酸、氨基氰和氰乙炔构建胞苷和尿苷核糖核苷酸的高产途径。如果甘油醛的对映体过量百分数大于或等于60% ,则该序列中的一个步骤允许拆分对映体纯的核糖氨基噁唑啉,这可能对生物同手性有意义。这可以被视为前生物纯化步骤,该化合物自发地从其他戊糖氨基恶唑啉的混合物中结晶出来。在无机磷酸盐的控制下,氨基恶唑啉能与氰乙炔温和高效地反应生成胞苷核糖核苷。利用紫外光进行光反耦合可以在1’端反转,从而得到正确的 β 立体化学反应;这种化学反应的一个问题是 α-胞苷在2’端的选择性磷酸化。然而,在2009年,它们展示了相同的简单构件允许通过磷酸盐控制的核碱基加工直接获得2 ',3 '-环嘧啶核苷酸,已知其能够聚合成RNA。有机化学家唐娜 · 布莱克蒙德将这一发现描述为 RNA 世界的“有力证据”。然而,约翰 · 萨瑟兰说,虽然他的团队的工作表明核酸在生命起源的早期扮演了核心的角色,但是它并不一定支持严格意义上的 RNA世界学说,他将其描述为一种“限制性的,假设性的安排”。

The Sutherland group's 2009 paper also highlighted the possibility for the photo-sanitization of the pyrimidine-2',3'-cyclic phosphates.[21] A potential weakness of these routes is the generation of enantioenriched glyceraldehyde, or its 3-phosphate derivative (glyceraldehyde prefers to exist as its keto tautomer dihydroxyacetone).[citation needed]


萨瑟兰集团2009年的论文还强调了对嘧啶 -2’,3’-环磷酸盐进行光消毒的可能性。这些路线的一个潜在弱点是生成对映异构的甘油醛或其3- 磷酸衍生物(甘油醛更喜欢作为其酮互变异构体二羟丙酮存在)。

[终译]萨瑟兰组2009年的论文还强调了对嘧啶 -2',3'-环磷酸盐进行光消毒的可能性。这些路线的一个潜在弱点是生成对映异构的甘油醛或其3- 磷酸衍生物(甘油醛更喜欢作为其酮互变异构体二羟丙酮的形式存在)。

On August 8, 2011, a report, based on NASA studies with meteorites found on Earth, was published suggesting building blocks of RNA (adenine, guanine, and related organic molecules) may have been formed in outer space.[54][55][56] In 2017, a numerical model suggests that the RNA world may have emerged in warm ponds on the early Earth, and that meteorites were a plausible and probable source of the RNA building blocks (ribose and nucleic acids) to these environments.[57] On August 29, 2012, astronomers at Copenhagen University reported the detection of a specific sugar molecule, glycolaldehyde, in a distant star system. The molecule was found around the protostellar binary IRAS 16293-2422, which is located 400 light years from Earth.[58][59] Because glycolaldehyde is needed to form RNA, this finding suggests that complex organic molecules may form in stellar systems prior to the formation of planets, eventually arriving on young planets early in their formation.[60]

2011年8月8日,一份基于 NASA 对地球上发现的陨石的研究的报告发表,报告指出 RNA (腺嘌呤、鸟嘌呤和相关的有机分子)可能已经在外层空间形成。2017年,一个数值模型表明,RNA 世界可能是在早期地球的温暖池塘中出现的,陨石可能是这些环境中 RNA 构建块(核糖和核酸)的一个合理和可能的来源。2012年8月29日,哥本哈根大学的天文学家报告说在一个遥远的恒星系统中发现了一种特殊的糖分子---- 乙醇醛。该分子是在距离地球400光年的原恒星双星 IRAS 16293-2422附近发现的。因为乙醇醛是形成 RNA 所必需的,这一发现表明,在行星形成之前,复杂的有机分子可能在恒星系统中形成,最终在年轻行星形成的早期到达。

[终译]2011年8月8日,一份基于美国宇航局对地球上发现的陨石进行研究的报告发表,报告指出 RNA(腺嘌呤、鸟嘌呤和相关的有机分子)可能已经在外层空间形成。2017年,一个数值模型表明,RNA 世界可能是在早期地球的温暖池塘中出现的,陨石可能是这些环境中 RNA 构建块(核糖和核酸)的一个合理和可能的来源。2012年8月29日,哥本哈根大学的天文学家报告说在一个遥远的恒星系统中发现了一种特殊的糖分子——乙醇醛。该分子是在距离地球400光年的原恒星双星IRAS 16293-2422附近发现的。因为乙醇醛是形成 RNA 所必需的,这一发现表明,在行星形成之前,复杂的有机分子可能在恒星系统中形成,最终在年轻行星形成的早期到达。

Prebiotic RNA synthesis

文件:Etls-2019-0024c.01.png
A schematic representation of the RNA world hypothesisRNA世界假说的示意图

Nucleotides are the fundamental molecules that combine in series to form RNA. They consist of a nitrogenous base attached to a sugar-phosphate backbone. RNA is made of long stretches of specific nucleotides arranged so that their sequence of bases carries information. The RNA world hypothesis holds that in the primordial soup (or sandwich), there existed free-floating nucleotides. These nucleotides regularly formed bonds with one another, which often broke because the change in energy was so low. However, certain sequences of base pairs have catalytic properties that lower the energy of their chain being created, enabling them to stay together for longer periods of time. As each chain grew longer, it attracted more matching nucleotides faster, causing chains to now form faster than they were breaking down.

生命起源前的 RNA 合成这是一个关于 RNA世界学说核苷酸的示意图,这些核苷酸是连续结合形成 RNA 的基本分子。它们由一个含氮硷基连接到一个糖磷酸骨架上。RNA 是由一长串特定的核苷酸组成的,这样它们的碱基序列就携带了信息。RNA世界学说认为,在原始汤(或三明治)中存在着自由漂浮的核苷酸。这些核苷酸有规律地彼此形成键,而这些键经常断裂,因为能量的变化很小。然而,某些碱基对序列具有催化特性,降低了它们被创造的链的能量,使它们能够在一起呆更长的时间。随着每个链变长,它吸引更多匹配核苷酸的速度更快,导致链现在形成的速度比它们分解的速度快。

[终译]核苷酸是串联组合形成RNA的基本分子。它们由一个含氮碱基连接到一个糖磷酸骨架上。RNA 是由一长串特定的核苷酸组成的,这样它们的碱基序列携带着信息。RNA世界学说认为,在原始汤(或三明治)中存在着自由漂浮的核苷酸。这些核苷酸有规律地彼此形成键,由于能量变化太低,这些键经常断裂。然而,某些碱基对序列具有催化特性,可以降低它们链的能量,使它们能够在更长的时间内保持在一起。随着每条链变长,它更快地吸引更多匹配的核苷酸,导致现在的链形成的速度比它们分解的速度快。

These chains have been proposed by some as the first, primitive forms of life. In an RNA world, different sets of RNA strands would have had different replication outputs, which would have increased or decreased their frequency in the population, i.e. natural selection. As the fittest sets of RNA molecules expanded their numbers, novel catalytic properties added by mutation, which benefitted their persistence and expansion, could accumulate in the population. Such an autocatalytic set of ribozymes, capable of self replication in about an hour, has been identified. It was produced by molecular competition (in vitro evolution) of candidate enzyme mixtures.[61]

这些链条被一些人认为是最早的原始生命形式。在 RNA 的世界里,不同的 RNA 链具有不同的复制输出,这会增加或减少它们在人群中的复制频率,即。自然选择。随着最适合的 RNA 分子数量的增加,通过突变添加的新的催化特性可以在种群中积累,这有利于它们的持久性和扩展性。这样一个核酶的自催化集,能够在一个小时内自我复制,已经被确定。它是通过候选酶混合物的分子竞争(体外进化)产生的。

[终译]有些人认为这些链是最初的原始生命形式。在 RNA 世界里,不同的 RNA 链具有不同的复制输出,这会增加或减少它们在种群中的复制频率,即自然选择。随着最适合的 RNA 分子数量的增加,通过突变添加的新的催化特性可以在种群中积累,这有利于它们的持续和扩展。这种能在大约一小时内自我复制的自催化核酶已经被鉴定出来。它是通过候选酶混合物的分子竞争(体外进化)产生的。

Competition between RNA may have favored the emergence of cooperation between different RNA chains, opening the way for the formation of the first protocell. Eventually, RNA chains developed with catalytic properties that help amino acids bind together (a process called peptide-bonding). These amino acids could then assist with RNA synthesis, giving those RNA chains that could serve as ribozymes the selective advantage. The ability to catalyze one step in protein synthesis, aminoacylation of RNA, has been demonstrated in a short (five-nucleotide) segment of RNA.[62]

RNA 之间的竞争可能有利于不同 RNA 链之间合作的出现,为第一个原始细胞的形成开辟了道路。最终,RNA 链具有催化特性,帮助氨基酸结合在一起(这个过程称为肽键)。这些氨基酸可以帮助 RNA 的合成,给予这些 RNA 链,可以作为核酶的选择性优势。在蛋白质合成的一个步骤,RNA 的氨基酰化,已经被证明在一个短的(五个核苷酸)片段的 RNA。

[终译]RNA 之间的竞争可能有利于不同 RNA 链之间合作的出现,为第一个原始细胞的形成开辟了道路。最终,RNA 链发展出催化特性,帮助氨基酸结合在一起(这个过程称为肽键合)。然后,这些氨基酸可以帮助 RNA 的合成,使那些可以充当核酶的RNA链具有选择性优势。催化蛋白质合成中的一个步骤,即RNA的氨酰化的能力,已经在RNA的一个短(五个核苷酸)片段中得到证实。

In March 2015, NASA scientists reported that, for the first time, complex DNA and RNA organic compounds of life, including uracil, cytosine, and thymine, have been formed in the laboratory under conditions found only in outer space, using starting chemicals, like pyrimidine, found in meteorites. Pyrimidine, like polycyclic aromatic hydrocarbons (PAHs), may have been formed in red giant stars or in interstellar dust and gas clouds, according to the scientists.[63]

2015年3月,美国宇航局的科学家报告说,复杂的 DNA 和 RNA 生命有机化合物,包括尿嘧啶、胞嘧啶和胸腺嘧啶,首次在实验室中形成,这些化合物只存在于外层空间,使用了陨石中发现的嘧啶等起始化学物质。据科学家说,嘧啶,像多环芳烃一样,可能是在红巨星或星际尘埃和气体云中形成的。

[终译]2015年3月,美国宇航局的科学家报告说,复杂的 DNA 和 RNA 生命有机化合物,包括尿嘧啶、胞嘧啶和胸腺嘧啶,首次在实验室中形成,这些化合物只存在于外层空间,使用了陨石中发现的嘧啶等起始化学物质。据科学家说,嘧啶像多环芳烃一样,可能是在红巨星或星际尘埃和气体云中形成的。

In 2018, researchers at Georgia Institute of Technology identified three molecular candidates for the bases that might have formed an earliest version of proto-RNA: barbituric acid, melamine, and 2,4,6-triaminopyrimidine (TAP). These three molecules are simpler versions of the four bases in current RNA, which could have been present in larger amounts and could still be forward-compatible with them, but may have been discarded by evolution in exchange for more optimal base pairs.[64] Specifically, TAP can form nucleotides with a large range of sugars.[65] Both TAP and melamine base pair with barbituric acid. All three spontaneously form nucleotides with ribose.[66]

2018年,佐治亚理工学院的研究人员确定了三种可能形成原始 rna 的候选碱基: 巴比妥酸、三聚氰胺和2,4,6- 三氨基嘧啶(TAP)。这三个分子是目前 RNA 中四个碱基的简化版本,可能存在大量的碱基,并且仍然可以与它们正向兼容,但是可能已经被进化所丢弃,以换取更多的最佳碱基对。具体来说,TAP 可以形成含有大量糖的核苷酸。TAP 和三聚氰胺碱都与巴比妥酸配对。所有三个自发形成核苷酸与核糖。

[终译]2018年,佐治亚理工学院的研究人员确定了三种可能形成原始 RNA的候选碱基:巴比妥酸、三聚氰胺和2,4,6- 三氨基嘧啶(TAP)。这三个分子是目前 RNA 中四种基的简化版本,可能存在大量的碱基,且仍然可以与它们正向兼容,但是可能已经被进化所丢弃,以换取更多的最佳碱基对。具体来说,TAP可以与大范围的糖形成核苷酸。TAP 和三聚氰胺碱基都与巴比妥酸配对。这三种物质都自发地与核糖形成核苷酸。

Evolution of DNA ==DNA的进化

One of the challenges posed by the RNA world hypothesis is to discover the pathway by which an RNA-based system transitioned to one based on DNA. Geoffrey Diemer and Ken Stedman, at Portland State University in Oregon, may have found a solution. While conducting a survey of viruses in a hot acidic lake in Lassen Volcanic National Park, California, they uncovered evidence that a simple DNA virus had acquired a gene from a completely unrelated RNA-based virus. Virologist Luis Villareal of the University of California Irvine also suggests that viruses capable of converting an RNA-based gene into DNA and then incorporating it into a more complex DNA-based genome might have been common in the Virus world during the RNA to DNA transition some 4 billion years ago.[67][68] This finding bolsters the argument for the transfer of information from the RNA world to the emerging DNA world before the emergence of the last universal common ancestor. From the research, the diversity of this virus world is still with us.

= = = DNA 的进化 = = RNA世界学说的挑战之一是发现基于 rna 的系统转变为基于 DNA 的系统的途径。俄勒冈州波特兰州立大学的杰弗里 · 迪默和肯 · 斯泰德曼可能已经找到了一个解决方案。他们在加利福尼亚拉森火山国家公园的一个热酸性湖泊中进行了一项病毒调查,发现了一个简单的 DNA 病毒从一个完全不相关的 rna 病毒中获得了一个基因的证据。加利福尼亚大学欧文分校的病毒学家路易斯 · 维拉里亚尔也认为,大约40亿年前,病毒世界在 RNA 到 DNA 的转变过程中,可能普遍存在病毒能够将一个基于 RNA 的基因转化为 DNA,然后将其整合到一个更复杂的基于 DNA 的基因组中。Bob Holmes (2012)“第一眼看到 DNA 的诞生”(《新科学家》2012年4月12日)这一发现支持了在最后一个普遍共同祖先出现之前,信息从 RNA 世界转移到新兴 DNA 世界的观点。从研究来看,这个病毒世界的多样性仍然存在。

[终译]RNA世界假说的挑战之一是发现基于RNA的系统转变为基于DNA的系统的途径。俄勒冈州波特兰州立大学的杰弗里 · 迪默和肯 · 斯泰德曼可能已经找到了一个解决方案。他们在加利福尼亚拉森火山国家公园的一个热酸性湖泊中进行了一项病毒调查,发现了一个简单的 DNA 病毒从一个完全不相关的RNA病毒中获得了一个基因的证据。加利福尼亚大学欧文分校的病毒学家路易斯 · 维拉里亚尔也认为,大约40亿年前,病毒世界在 RNA 到 DNA 的转变过程中,可能普遍存在病毒能够将一个基于 RNA 的基因转化为 DNA,然后将其整合到一个更复杂的基于 DNA 的基因组中。这一发现支持了在最后一个普遍共同祖先出现之前,信息从 RNA 世界转移到新兴 DNA 世界的观点。从研究来看,这个病毒世界的多样性仍然存在。

Viroids ==类病毒==

Additional evidence supporting the concept of an RNA world has resulted from research on viroids, the first representatives of a novel domain of "subviral pathogens".[69][70] Viroids infect plants, where most are pathogens, and consist of short stretches of highly complementary, circular, single-stranded and non-coding RNA without a protein coat. They are extremely small, ranging from 246 to 467 nucleobases, compared to the smallest known viruses capable of causing an infection, with genomes about 2,000 nucleobases in length.[71]

Additional evidence supporting the concept of an RNA world has resulted from research on viroids, the first representatives of a novel domain of "subviral pathogens". Viroids infect plants, where most are pathogens, and consist of short stretches of highly complementary, circular, single-stranded and non-coding RNA without a protein coat. They are extremely small, ranging from 246 to 467 nucleobases, compared to the smallest known viruses capable of causing an infection, with genomes about 2,000 nucleobases in length.

支持 RNA 世界概念的其他证据来自对类病毒的研究,这是“亚病毒病原体”这一新领域的第一个代表。病毒感染植物,其中大多数是病原体,并包括短期高度互补,圆形,单链和非编码 RNA 没有蛋白质外壳。与已知能够引起感染的最小病毒相比,它们极其微小,从246到467个碱基不等,基因组中约有2000个碱基长度。

[终译]支持 RNA 世界概念的其他证据来自对类病毒的研究,这是“亚病毒病原体”这一新领域的第一个代表。病毒感染植物,其中大多数是病原体,并包括短期高度互补,圆形,单链和非编码 RNA 没有蛋白质外壳。与已知能够引起感染的最小病毒相比,它们极其微小,从246到467个碱基不等,基因组中约有2000个碱基长度。

Based on their characteristic properties, in 1989 plant biologist Theodor Diener argued that viroids are more plausible living relics of the RNA world than introns and other RNAs considered candidates at the time.[72] Diener's hypothesis would be expanded by the research group of Ricardo Flores,[73][74] and gained a broader audience when in 2014, a New York Times science writer published a popularized version of the proposal.[75]

Based on their characteristic properties, in 1989 plant biologist Theodor Diener argued that viroids are more plausible living relics of the RNA world than introns and other RNAs considered candidates at the time. Diener's hypothesis would be expanded by the research group of Ricardo Flores, and gained a broader audience when in 2014, a New York Times science writer published a popularized version of the proposal.

1989年,植物生物学家西奥多 · 迪纳根据病毒的特性认为,与当时被认为是候选的内含子和其他 RNA 相比,类病毒更像是 RNA 世界的活遗迹。迪纳的假设将由里卡多 · 弗洛雷斯的研究小组进一步扩展,并在2014年获得了更广泛的受众,当时《纽约时报》的一位科普作家发表了一个普及版的提案。

[终译]1989年,植物生物学家西奥多 · 迪纳根据病毒的特性认为,与当时被认为是候选的内含子和其他 RNA 相比,类病毒更像是 RNA 世界的活遗迹。迪纳的假设将由里卡多 · 弗洛雷斯的研究小组进一步扩展,并在2014年获得了更广泛的受众,当时《纽约时报》的一位科普作家发表了一个普及版的提案。

The characteristics of viroids highlighted as consistent with an RNA world were their small size, high guanine and cytosine content, circular structure, structural periodicity, the lack of protein-coding ability and, in some cases, ribozyme-mediated replication.[74] One aspect critics of the hypothesis have focused on is that the exclusive hosts of all known viroids, angiosperms, did not evolve until billions of years after the RNA world was replaced, making viroids more likely to have arisen through later evolutionary mechanisms unrelated to the RNA world than to have survived via a cryptic host over that extended period.[76] Whether they are relics of that world or of more recent origin, their function as autonomous naked RNA is seen as analogous to that envisioned for an RNA world.

The characteristics of viroids highlighted as consistent with an RNA world were their small size, high guanine and cytosine content, circular structure, structural periodicity, the lack of protein-coding ability and, in some cases, ribozyme-mediated replication. One aspect critics of the hypothesis have focused on is that the exclusive hosts of all known viroids, angiosperms, did not evolve until billions of years after the RNA world was replaced, making viroids more likely to have arisen through later evolutionary mechanisms unrelated to the RNA world than to have survived via a cryptic host over that extended period. Whether they are relics of that world or of more recent origin, their function as autonomous naked RNA is seen as analogous to that envisioned for an RNA world.

与 RNA 世界相一致的是,类病毒的特点是体积小、鸟嘌呤和胞嘧啶含量高、环状结构、结构周期性、缺乏蛋白质编码能力,在某些情况下还有核酶介导的复制。这一假说的批评者关注的一个方面是,所有已知的类病毒---- 被子植物---- 的独特宿主直到 RNA 世界被取代数十亿年后才进化出来,这使得类病毒更有可能是通过与 RNA 世界无关的后期进化机制产生的,而不是通过一个神秘宿主存活了很长时间。无论它们是那个世界的遗物还是最近的起源,它们作为自主裸 RNA 的功能被视为类似于 RNA 世界的设想。

[终译]与 RNA 世界相一致的是,类病毒的特点是体积小、鸟嘌呤和胞嘧啶含量高、环状结构、结构周期性、缺乏蛋白质编码能力,在某些情况下还有核酶介导的复制。这一假说的批评者关注的一个方面是,所有已知的类病毒---- 被子植物---- 的独特宿主直到 RNA 世界被取代数十亿年后才进化出来,这使得类病毒更有可能是通过与 RNA 世界无关的后期进化机制产生的,而不是通过一个神秘宿主存活了很长时间。无论它们是那个世界的遗物还是最近的起源,它们作为自主裸 RNA 的功能被视为类似于 RNA 世界的设想。

Origin of sexual reproduction==有性繁殖的起源==

模板:Further

Eigen et al.[77] and Woese[78] proposed that the genomes of early protocells were composed of single-stranded RNA, and that individual genes corresponded to separate RNA segments, rather than being linked end-to-end as in present-day DNA genomes. A protocell that was haploid (one copy of each RNA gene) would be vulnerable to damage, since a single lesion in any RNA segment would be potentially lethal to the protocell (e.g. by blocking replication or inhibiting the function of an essential gene).

Eigen et al. and WoeseWoese CR (1983). The primary lines of descent and the universal ancestor. Chapter in pp. 209-233. proposed that the genomes of early protocells were composed of single-stranded RNA, and that individual genes corresponded to separate RNA segments, rather than being linked end-to-end as in present-day DNA genomes. A protocell that was haploid (one copy of each RNA gene) would be vulnerable to damage, since a single lesion in any RNA segment would be potentially lethal to the protocell (e.g. by blocking replication or inhibiting the function of an essential gene).

埃根等。及 WoeseWoese CR (1983)。世系的基本线和普遍祖先。第二章。209-233.提出早期原始细胞的基因组是由单链 RNA 组成的,个体基因对应于单独的 RNA 片段,而不是像现在的 DNA 基因组那样端对端连接。单倍体的原始细胞(每个 RNA 基因的一个拷贝)容易受到损伤,因为任何 RNA 片段中的单个损伤都可能对原始细胞致死(例如:。通过阻止复制或抑制必需基因的功能)。

[终译]埃根等。及 WoeseWoese CR (1983)。世系的基本线和普遍祖先。第二章。209-233.提出早期原始细胞的基因组是由单链 RNA 组成的,个体基因对应于单独的 RNA 片段,而不是像现在的 DNA 基因组那样端对端连接。单倍体的原始细胞(每个 RNA 基因的一个拷贝)容易受到损伤,因为任何 RNA 片段中的单个损伤都可能对原始细胞致死(例如:。通过阻止复制或抑制必需基因的功能)。

Vulnerability to damage could be reduced by maintaining two or more copies of each RNA segment in each protocell, i.e. by maintaining diploidy or polyploidy. Genome redundancy would allow a damaged RNA segment to be replaced by an additional replication of its homolog. However, for such a simple organism, the proportion of available resources tied up in the genetic material would be a large fraction of the total resource budget. Under limited resource conditions, the protocell reproductive rate would likely be inversely related to ploidy number. The protocell's fitness would be reduced by the costs of redundancy. Consequently, coping with damaged RNA genes while minimizing the costs of redundancy would likely have been a fundamental problem for early protocells.

Vulnerability to damage could be reduced by maintaining two or more copies of each RNA segment in each protocell, i.e. by maintaining diploidy or polyploidy. Genome redundancy would allow a damaged RNA segment to be replaced by an additional replication of its homolog. However, for such a simple organism, the proportion of available resources tied up in the genetic material would be a large fraction of the total resource budget. Under limited resource conditions, the protocell reproductive rate would likely be inversely related to ploidy number. The protocell's fitness would be reduced by the costs of redundancy. Consequently, coping with damaged RNA genes while minimizing the costs of redundancy would likely have been a fundamental problem for early protocells.

保持每个原始细胞中每个 RNA 片段的两个或两个以上拷贝,可以降低受损害的脆弱性。保持二倍性或多倍性。基因组冗余将使受损的 RNA 片段被其同源基因的额外复制所取代。然而,对于这样一个简单的生物体而言,与遗传材料有关的可用资源的比例将占资源总预算的很大一部分。在有限的资源条件下,原细胞的繁殖率可能与倍性数成反比。原始细胞的适应性会因冗余成本而降低。因此,在处理受损的 RNA 基因的同时尽量减少冗余成本可能是早期原始细胞的一个基本问题。

[终译]保持每个原始细胞中每个 RNA 片段的两个或两个以上拷贝,可以降低受损害的脆弱性。保持二倍性或多倍性。基因组冗余将使受损的 RNA 片段被其同源基因的额外复制所取代。然而,对于这样一个简单的生物体而言,与遗传材料有关的可用资源的比例将占资源总预算的很大一部分。在有限的资源条件下,原细胞的繁殖率可能与倍性数成反比。原始细胞的适应性会因冗余成本而降低。因此,在处理受损的 RNA 基因的同时尽量减少冗余成本可能是早期原始细胞的一个基本问题。

A cost-benefit analysis was carried out in which the costs of maintaining redundancy were balanced against the costs of genome damage.[79] This analysis led to the conclusion that, under a wide range of circumstances, the selected strategy would be for each protocell to be haploid, but to periodically fuse with another haploid protocell to form a transient diploid. The retention of the haploid state maximizes the growth rate. The periodic fusions permit mutual reactivation of otherwise lethally damaged protocells. If at least one damage-free copy of each RNA gene is present in the transient diploid, viable progeny can be formed. For two, rather than one, viable daughter cells to be produced would require an extra replication of the intact RNA gene homologous to any RNA gene that had been damaged prior to the division of the fused protocell. The cycle of haploid reproduction, with occasional fusion to a transient diploid state, followed by splitting to the haploid state, can be considered to be the sexual cycle in its most primitive form.[79][80] In the absence of this sexual cycle, haploid protocells with damage in an essential RNA gene would simply die.

A cost-benefit analysis was carried out in which the costs of maintaining redundancy were balanced against the costs of genome damage. This analysis led to the conclusion that, under a wide range of circumstances, the selected strategy would be for each protocell to be haploid, but to periodically fuse with another haploid protocell to form a transient diploid. The retention of the haploid state maximizes the growth rate. The periodic fusions permit mutual reactivation of otherwise lethally damaged protocells. If at least one damage-free copy of each RNA gene is present in the transient diploid, viable progeny can be formed. For two, rather than one, viable daughter cells to be produced would require an extra replication of the intact RNA gene homologous to any RNA gene that had been damaged prior to the division of the fused protocell. The cycle of haploid reproduction, with occasional fusion to a transient diploid state, followed by splitting to the haploid state, can be considered to be the sexual cycle in its most primitive form. see pgs. 293-297 In the absence of this sexual cycle, haploid protocells with damage in an essential RNA gene would simply die.

实施了一项成本-收益分析计划,其中维持冗余的成本与基因组损坏的成本相平衡。这项分析得出的结论是,在大范围的环境下,选择的策略是使每个原始细胞成为单倍体,但是定期与另一个单倍体细胞融合,形成一个暂时的二倍体。单倍体状态的保持使生长率最大化。这种周期性的融合允许原始细胞的相互重新激活,否则原始细胞就会遭到致命的破坏。如果每个 RNA 基因在瞬时二倍体中至少存在一个无损伤拷贝,则可形成有活力的后代。对于两个,而不是一个,可行的子细胞将需要额外的复制完整的 RNA 基因的同源 RNA 基因的任何 RNA 基因已经受损前的融合原细胞分裂。单倍体的繁殖周期,偶尔融合到短暂的二倍体状态,然后分裂到单倍体状态,可以被认为是最原始形式的性周期。参见 pgs。293-297如果没有这种有性周期,单倍体原始细胞如果在核糖核酸基因上有损伤,就会死亡。

[终译]实施了一项成本-收益分析计划,其中维持冗余的成本与基因组损坏的成本相平衡。这项分析得出的结论是,在大范围的环境下,选择的策略是使每个原始细胞成为单倍体,但是定期与另一个单倍体细胞融合,形成一个暂时的二倍体。单倍体状态的保持使生长率最大化。这种周期性的融合允许原始细胞的相互重新激活,否则原始细胞就会遭到致命的破坏。如果每个 RNA 基因在瞬时二倍体中至少存在一个无损伤拷贝,则可形成有活力的后代。对于两个,而不是一个,可行的子细胞将需要额外的复制完整的 RNA 基因的同源 RNA 基因的任何 RNA 基因已经受损前的融合原细胞分裂。单倍体的繁殖周期,偶尔融合到短暂的二倍体状态,然后分裂到单倍体状态,可以被认为是最原始形式的性周期。参见 pgs。293-297如果没有这种有性周期,单倍体原始细胞如果在核糖核酸基因上有损伤,就会死亡。

This model for the early sexual cycle is hypothetical, but it is very similar to the known sexual behavior of the segmented RNA viruses, which are among the simplest organisms known. Influenza virus, whose genome consists of 8 physically separated single-stranded RNA segments,[81] is an example of this type of virus. In segmented RNA viruses, "mating" can occur when a host cell is infected by at least two virus particles. If these viruses each contain an RNA segment with a lethal damage, multiple infection can lead to reactivation providing that at least one undamaged copy of each virus gene is present in the infected cell. This phenomenon is known as "multiplicity reactivation". Multiplicity reactivation has been reported to occur in influenza virus infections after induction of RNA damage by UV-irradiation,[82] and ionizing radiation.[83]

This model for the early sexual cycle is hypothetical, but it is very similar to the known sexual behavior of the segmented RNA viruses, which are among the simplest organisms known. Influenza virus, whose genome consists of 8 physically separated single-stranded RNA segments, is an example of this type of virus. In segmented RNA viruses, "mating" can occur when a host cell is infected by at least two virus particles. If these viruses each contain an RNA segment with a lethal damage, multiple infection can lead to reactivation providing that at least one undamaged copy of each virus gene is present in the infected cell. This phenomenon is known as "multiplicity reactivation". Multiplicity reactivation has been reported to occur in influenza virus infections after induction of RNA damage by UV-irradiation, and ionizing radiation.

这个关于早期性周期的模型是假设的,但是它与已知的分节 RNA 病毒的性行为非常相似,这是已知的最简单的生物体之一。流感病毒就是这类病毒的一个例子,它的基因组由8个物理分离的单链 RNA 片段组成。在分节 RNA 病毒中,当宿主细胞被至少两种病毒颗粒感染时,就会发生“交配”。如果这些病毒每个都含有一个具有致命损伤的 RNA 片段,多重感染可以导致重新激活,条件是每个病毒基因的至少一个未受损的拷贝存在于被感染的细胞中。这种现象被称为“多重复激活”。据报道,在流感病毒感染中,经紫外线和电离辐射诱导 RNA 损伤后,会发生多重再激活。

[终译]这个关于早期性周期的模型是假设的,但是它与已知的分节 RNA 病毒的性行为非常相似,这是已知的最简单的生物体之一。流感病毒就是这类病毒的一个例子,它的基因组由8个物理分离的单链 RNA 片段组成。在分节 RNA 病毒中,当宿主细胞被至少两种病毒颗粒感染时,就会发生“交配”。如果这些病毒每个都含有一个具有致命损伤的 RNA 片段,多重感染可以导致重新激活,条件是每个病毒基因的至少一个未受损的拷贝存在于被感染的细胞中。这种现象被称为“多重复激活”。据报道,在流感病毒感染中,经紫外线和电离辐射诱导 RNA 损伤后,会发生多重再激活。

Further developments==进一步的发展==

模板:Further Patrick Forterre has been working on a novel hypothesis, called "three viruses, three domains":[84] that viruses were instrumental in the transition from RNA to DNA and the evolution of Bacteria, Archaea, and Eukaryota. He believes the last universal common ancestor[84] was RNA-based and evolved RNA viruses. Some of the viruses evolved into DNA viruses to protect their genes from attack. Through the process of viral infection into hosts the three domains of life evolved.[84][85]


Patrick Forterre has been working on a novel hypothesis, called "three viruses, three domains": that viruses were instrumental in the transition from RNA to DNA and the evolution of Bacteria, Archaea, and Eukaryota. He believes the last universal common ancestor was RNA-based and evolved RNA viruses. Some of the viruses evolved into DNA viruses to protect their genes from attack. Through the process of viral infection into hosts the three domains of life evolved.

进一步的发展帕特里克 · 福特尔一直致力于一个新的假设,称为“三病毒,三域”: 病毒在从 RNA 到 DNA 的转变和细菌、 Archaea 和 Eukaryota 的进化过程中起着重要作用。他认为最后的共同祖先是基于 RNA 的进化出来的 RNA 病毒。一些病毒进化成 DNA 病毒,以保护其基因免受攻击。通过病毒感染宿主的过程,生命的三个领域得以进化。

[终译]进一步的发展帕特里克 · 福特尔一直致力于一个新的假设,称为“三病毒,三域”: 病毒在从 RNA 到 DNA 的转变和细菌、 Archaea 和 Eukaryota 的进化过程中起着重要作用。他认为最后的共同祖先是基于 RNA 的进化出来的 RNA 病毒。一些病毒进化成 DNA 病毒,以保护其基因免受攻击。通过病毒感染宿主的过程,生命的三个领域得以进化。

Another interesting proposal is the idea that RNA synthesis might have been driven by temperature gradients, in the process of thermosynthesis.[86] Single nucleotides have been shown to catalyze organic reactions.[87]

Another interesting proposal is the idea that RNA synthesis might have been driven by temperature gradients, in the process of thermosynthesis. Single nucleotides have been shown to catalyze organic reactions.

另一个有趣的提议是,RNA 合成可能是在热合成过程中由温度梯度驱动的。单核苷酸已被证明能够催化有机反应。

[终译]另一个有趣的提议是,RNA 合成可能是在热合成过程中由温度梯度驱动的。单核苷酸已被证明能够催化有机反应。

Steven Benner has argued that chemical conditions on the planet Mars, such as the presence of boron, molybdenum, and oxygen, may have been better for initially producing RNA molecules than those on Earth. If so, life-suitable molecules, originating on Mars, may have later migrated to Earth via mechanisms of panspermia or similar process.[88][89]

Steven Benner has argued that chemical conditions on the planet Mars, such as the presence of boron, molybdenum, and oxygen, may have been better for initially producing RNA molecules than those on Earth. If so, life-suitable molecules, originating on Mars, may have later migrated to Earth via mechanisms of panspermia or similar process.

史蒂芬 · 本纳认为,火星上的化学条件,比如硼、钼和氧的存在,可能比地球上的条件更有利于最初产生 RNA 分子。如果是这样的话,原产于火星的适合生命的分子可能后来通过胚种说或类似的过程迁移到了地球。

[终译]史蒂芬 · 本纳认为,火星上的化学条件,比如硼、钼和氧的存在,可能比地球上的条件更有利于最初产生 RNA 分子。如果是这样的话,原产于火星的适合生命的分子可能后来通过胚种说或类似的过程迁移到了地球。

Alternative hypotheses== 替代假设 ==

The hypothesized existence of an RNA world does not exclude a "Pre-RNA world", where a metabolic system based on a different nucleic acid is proposed to pre-date RNA. A candidate nucleic acid is peptide nucleic acid (PNA), which uses simple peptide bonds to link nucleobases.[90] PNA is more stable than RNA, but its ability to be generated under prebiological conditions has yet to be demonstrated experimentally.

The hypothesized existence of an RNA world does not exclude a "Pre-RNA world", where a metabolic system based on a different nucleic acid is proposed to pre-date RNA. A candidate nucleic acid is peptide nucleic acid (PNA), which uses simple peptide bonds to link nucleobases. PNA is more stable than RNA, but its ability to be generated under prebiological conditions has yet to be demonstrated experimentally.

RNA 世界的假设存在并不排除“前 RNA 世界”,其中提出了一种基于不同核酸的新陈代谢系统,以提前核糖核酸。一种候选的核酸是肽核酸,它利用简单的肽键连接碱基。PNA 比 RNA 更稳定,但其在前生物条件下生成的能力还有待于实验证实。

[终译]RNA 世界的假设存在并不排除“前 RNA 世界”,其中提出了一种基于不同核酸的新陈代谢系统,以提前核糖核酸。一种候选的核酸是肽核酸,它利用简单的肽键连接碱基。PNA 比 RNA 更稳定,但其在前生物条件下生成的能力还有待于实验证实。

Threose nucleic acid (TNA) has also been proposed as a starting point, as has glycol nucleic acid (GNA), and like PNA, also lack experimental evidence for their respective abiogenesis.

Threose nucleic acid (TNA) has also been proposed as a starting point, as has glycol nucleic acid (GNA), and like PNA, also lack experimental evidence for their respective abiogenesis.

苏糖核酸(TNA)也被提议作为一个起点,就像 GNA (GNA) ,和 PNA 一样,也缺乏各自自然发生的实验证据。

[终译]苏糖核酸(TNA)也被提议作为一个起点,就像 GNA (GNA) ,和 PNA 一样,也缺乏各自自然发生的实验证据。

An alternative—or complementary—theory of RNA origin is proposed in the PAH world hypothesis, whereby polycyclic aromatic hydrocarbons (PAHs) mediate the synthesis of RNA molecules.[91] PAHs are the most common and abundant of the known polyatomic molecules in the visible Universe, and are a likely constituent of the primordial sea.[92] PAHs and fullerenes (also implicated in the origin of life)[93] have been detected in nebulae.[94]

An alternative—or complementary—theory of RNA origin is proposed in the PAH world hypothesis, whereby polycyclic aromatic hydrocarbons (PAHs) mediate the synthesis of RNA molecules.Platts, Simon Nicholas, "The PAH World – Discotic polynuclear aromatic compounds as a mesophase scaffolding at the origin of life" PAHs are the most common and abundant of the known polyatomic molecules in the visible Universe, and are a likely constituent of the primordial sea.Allamandola, Louis et Al. "Cosmic Distribution of Chemical Complexity" PAHs and fullerenes (also implicated in the origin of life) have been detected in nebulae.

在《 PAH世界学说提出了一种替代或补充的 RNA 起源理论,即多环芳烃介导 RNA 分子的合成。多环芳烃是可见宇宙中最常见和最丰富的已知多原子分子,可能是原始海洋的组成部分。阿拉曼多拉,路易斯等。在星云中检测到「化学复杂性的宇宙分布」多环芳烃和富勒烯(亦与生命的起源有关)。

[终译]在《 PAH世界学说提出了一种替代或补充的 RNA 起源理论,即多环芳烃介导 RNA 分子的合成。多环芳烃是可见宇宙中最常见和最丰富的已知多原子分子,可能是原始海洋的组成部分。阿拉曼多拉,路易斯等。在星云中检测到「化学复杂性的宇宙分布」多环芳烃和富勒烯(亦与生命的起源有关)。

The iron-sulfur world theory proposes that simple metabolic processes developed before genetic materials did, and these energy-producing cycles catalyzed the production of genes.

The iron-sulfur world theory proposes that simple metabolic processes developed before genetic materials did, and these energy-producing cycles catalyzed the production of genes.

铁硫世界理论认为,简单的代谢过程比遗传物质发展得更早,而这些能量生产周期催化了基因的产生。

[终译]铁硫世界理论认为,简单的代谢过程比遗传物质发展得更早,而这些能量生产周期催化了基因的产生。

Some of the difficulties of producing the precursors on earth are bypassed by another alternative or complementary theory for their origin, panspermia. It discusses the possibility that the earliest life on this planet was carried here from somewhere else in the galaxy, possibly on meteorites similar to the Murchison meteorite.[95] Sugar molecules, including ribose, have been found in meteorites.[96][97] Panspermia does not invalidate the concept of an RNA world, but posits that this world or its precursors originated not on Earth but rather another, probably older, planet.

Some of the difficulties of producing the precursors on earth are bypassed by another alternative or complementary theory for their origin, panspermia. It discusses the possibility that the earliest life on this planet was carried here from somewhere else in the galaxy, possibly on meteorites similar to the Murchison meteorite. Sugar molecules, including ribose, have been found in meteorites. Panspermia does not invalidate the concept of an RNA world, but posits that this world or its precursors originated not on Earth but rather another, probably older, planet.

在地球上生产先质的一些困难被另一种关于它们起源的替代或补充理论——胚种说所绕过。它讨论了这个星球上最早的生命可能来自银河系的其他地方,可能存在于类似默奇森陨石的陨石上。在陨石中发现了糖分子,包括核糖。胚种说并没有否定 RNA 世界的概念,而是假定这个世界或其前身并非起源于地球,而是起源于另一个可能更古老的行星。

[终译]在地球上生产先质的一些困难被另一种关于它们起源的替代或补充理论——胚种说所绕过。它讨论了这个星球上最早的生命可能来自银河系的其他地方,可能存在于类似默奇森陨石的陨石上。在陨石中发现了糖分子,包括核糖。胚种说并没有否定 RNA 世界的概念,而是假定这个世界或其前身并非起源于地球,而是起源于另一个可能更古老的行星。

The relative chemical complexity of the nucleotide and the unlikelihood of it spontaneously arising, along with the limited number of combinations possible among four base forms, as well as the need for RNA polymers of some length before seeing enzymatic activity, have led some to reject the RNA world hypothesis in favor of a metabolism-first hypothesis, where the chemistry underlying cellular function arose first, along with the ability to replicate and facilitate this metabolism.

The relative chemical complexity of the nucleotide and the unlikelihood of it spontaneously arising, along with the limited number of combinations possible among four base forms, as well as the need for RNA polymers of some length before seeing enzymatic activity, have led some to reject the RNA world hypothesis in favor of a metabolism-first hypothesis, where the chemistry underlying cellular function arose first, along with the ability to replicate and facilitate this metabolism.

核苷酸的相对化学复杂性和它自发产生的不可能性,加上4种碱基形式之间可能的组合数量有限,以及在看到酶活性之前需要一定长度的 RNA 聚合物,导致一些人放弃了 RNA世界学说,转而支持新陈代谢优先假说,即细胞功能首先产生的化学基础,以及复制和促进这种新陈代谢的能力。

[终译]核苷酸的相对化学复杂性和它自发产生的不可能性,加上4种碱基形式之间可能的组合数量有限,以及在看到酶活性之前需要一定长度的 RNA 聚合物,导致一些人放弃了 RNA世界学说,转而支持新陈代谢优先假说,即细胞功能首先产生的化学基础,以及复制和促进这种新陈代谢的能力。

RNA-peptide coevolution = =RNA-多肽协同演化= =

Another proposal is that the dual-molecule system we see today, where a nucleotide-based molecule is needed to synthesize protein, and a peptide-based (protein) molecule is needed to make nucleic acid polymers, represents the original form of life.[98] This theory is called RNA-peptide coevolution,[99] or the Peptide-RNA world, and offers a possible explanation for the rapid evolution of high-quality replication in RNA (since proteins are catalysts), with the disadvantage of having to postulate the coincident formation of two complex molecules, an enzyme (from peptides) and a RNA (from nucleotides). In this Peptide-RNA World scenario, RNA would have contained the instructions for life, while peptides (simple protein enzymes) would have accelerated key chemical reactions to carry out those instructions.[100] The study leaves open the question of exactly how those primitive systems managed to replicate themselves — something neither the RNA World hypothesis nor the Peptide-RNA World theory can yet explain, unless polymerases (enzymes that rapidly assemble the RNA molecule) played a role.[100]

Another proposal is that the dual-molecule system we see today, where a nucleotide-based molecule is needed to synthesize protein, and a peptide-based (protein) molecule is needed to make nucleic acid polymers, represents the original form of life. This theory is called RNA-peptide coevolution, or the Peptide-RNA world, and offers a possible explanation for the rapid evolution of high-quality replication in RNA (since proteins are catalysts), with the disadvantage of having to postulate the coincident formation of two complex molecules, an enzyme (from peptides) and a RNA (from nucleotides). In this Peptide-RNA World scenario, RNA would have contained the instructions for life, while peptides (simple protein enzymes) would have accelerated key chemical reactions to carry out those instructions. The study leaves open the question of exactly how those primitive systems managed to replicate themselves — something neither the RNA World hypothesis nor the Peptide-RNA World theory can yet explain, unless polymerases (enzymes that rapidly assemble the RNA molecule) played a role.

另一个提议是,我们今天看到的双分子系统,需要一个基于核苷酸的分子来合成蛋白质,需要一个基于肽(蛋白质)的分子来制造核酸聚合物,代表了生命的原始形式。这一理论被称为 RNA-肽协同进化,或称为肽-RNA 世界,它为 RNA 中高质量复制的快速进化提供了一种可能的解释(因为蛋白质是催化剂) ,但其缺点是必须假定两个复杂分子——一个酶(来自肽)和一个 RNA (来自核苷酸)的同步形成。在这个多肽-RNA 世界的场景中,RNA 包含了生命的指令,而多肽(简单的蛋白酶)可以加速关键的化学反应来执行这些指令。这项研究留下了一个问题,那就是这些原始系统究竟是如何设法自我复制的——无论是 RNA世界学说还是肽-RNA 世界理论都无法解释这个问题,除非聚合酶(快速组装 RNA 分子的酶)发挥了作用。

[终译]另一个提议是,我们今天看到的双分子系统,需要一个基于核苷酸的分子来合成蛋白质,需要一个基于肽(蛋白质)的分子来制造核酸聚合物,代表了生命的原始形式。这一理论被称为 RNA-肽协同进化,或称为肽-RNA 世界,它为 RNA 中高质量复制的快速进化提供了一种可能的解释(因为蛋白质是催化剂) ,但其缺点是必须假定两个复杂分子——一个酶(来自肽)和一个 RNA (来自核苷酸)的同步形成。在这个多肽-RNA 世界的场景中,RNA 包含了生命的指令,而多肽(简单的蛋白酶)可以加速关键的化学反应来执行这些指令。这项研究留下了一个问题,那就是这些原始系统究竟是如何设法自我复制的——无论是 RNA世界学说还是肽-RNA 世界理论都无法解释这个问题,除非聚合酶(快速组装 RNA 分子的酶)发挥了作用。

A research project completed in March 2015 by the Sutherland group found that a network of reactions beginning with hydrogen cyanide and hydrogen sulfide, in streams of water irradiated by UV light, could produce the chemical components of proteins and lipids, alongside those of RNA.[101][102] The researchers used the term "cyanosulfidic" to describe this network of reactions.[101] In November 2017, a team at the Scripps Research Institute identified reactions involving the compound diamidophosphate which could have linked the chemical components into short peptide and lipid chains as well as short RNA-like chains of nucleotides.[103][104]

A research project completed in March 2015 by the Sutherland group found that a network of reactions beginning with hydrogen cyanide and hydrogen sulfide, in streams of water irradiated by UV light, could produce the chemical components of proteins and lipids, alongside those of RNA. The researchers used the term "cyanosulfidic" to describe this network of reactions. In November 2017, a team at the Scripps Research Institute identified reactions involving the compound diamidophosphate which could have linked the chemical components into short peptide and lipid chains as well as short RNA-like chains of nucleotides.

2015年3月,Sutherland 小组完成的一个研究项目发现,以氰化氢和硫化氢为起始的反应网络,在紫外线照射下的水流中,可以产生蛋白质和脂类的化学成分,以及 RNA 的化学成分。研究人员用“氰磺酸盐”这个术语来描述这个反应网络。2017年11月,斯克里普斯研究所的一个研究小组确认了涉及化合物磷酸二胺的反应,磷酸二胺可以将化学成分连接成短肽和脂质链,以及类似 rna 的短核苷酸链。

[终译]2015年3月,Sutherland 小组完成的一个研究项目发现,以氰化氢和硫化氢为起始的反应网络,在紫外线照射下的水流中,可以产生蛋白质和脂类的化学成分,以及 RNA 的化学成分。研究人员用“氰磺酸盐”这个术语来描述这个反应网络。2017年11月,斯克里普斯研究所的一个研究小组确认了涉及化合物磷酸二胺的反应,磷酸二胺可以将化学成分连接成短肽和脂质链,以及类似 rna 的短核苷酸链。

Implications == 影响 ==

The RNA world hypothesis, if true, has important implications for the definition of life. For most of the time that followed Franklin, Watson and Crick's elucidation of DNA structure in 1953, life was largely defined in terms of DNA and proteins: DNA and proteins seemed the dominant macromolecules in the living cell, with RNA only aiding in creating proteins from the DNA blueprint.

The RNA world hypothesis, if true, has important implications for the definition of life. For most of the time that followed Franklin, Watson and Crick's elucidation of DNA structure in 1953, life was largely defined in terms of DNA and proteins: DNA and proteins seemed the dominant macromolecules in the living cell, with RNA only aiding in creating proteins from the DNA blueprint.

RNA世界学说,如果是真的,对生命的定义有着重要的影响。在1953年沃森与克里克 · 富兰克林对 DNA 结构进行解释之后的大部分时间里,生命在很大程度上被定义为 DNA 和蛋白质: DNA 和蛋白质似乎是活细胞中占主导地位的大分子,而 RNA 只能帮助从 DNA 蓝图中创造蛋白质。

[终译]RNA世界学说,如果是真的,对生命的定义有着重要的影响。在1953年沃森与克里克 · 富兰克林对 DNA 结构进行解释之后的大部分时间里,生命在很大程度上被定义为 DNA 和蛋白质: DNA 和蛋白质似乎是活细胞中占主导地位的大分子,而 RNA 只能帮助从 DNA 蓝图中创造蛋白质。

The RNA world hypothesis places RNA at center-stage when life originated. The RNA world hypothesis is supported by the observations that ribosomes are ribozymes:[105][106] the catalytic site is composed of RNA, and proteins hold no major structural role and are of peripheral functional importance. This was confirmed with the deciphering of the 3-dimensional structure of the ribosome in 2001. Specifically, peptide bond formation, the reaction that binds amino acids together into proteins, is now known to be catalyzed by an adenine residue in the rRNA.

The RNA world hypothesis places RNA at center-stage when life originated. The RNA world hypothesis is supported by the observations that ribosomes are ribozymes: the catalytic site is composed of RNA, and proteins hold no major structural role and are of peripheral functional importance. This was confirmed with the deciphering of the 3-dimensional structure of the ribosome in 2001. Specifically, peptide bond formation, the reaction that binds amino acids together into proteins, is now known to be catalyzed by an adenine residue in the rRNA.

生命起源时,RNA世界学说把 RNA 放在中心位置。核糖体是核酶的观察结果支持了 RNA世界学说的观点: 核糖体的催化位点是由 RNA 组成的,蛋白质没有主要的结构作用,具有次要的功能重要性。这一点在2001年核糖体三维结构的破译中得到了证实。具体来说,肽键的形成,即将氨基酸结合成蛋白质的反应,现在已知是由 rna 中的腺嘌呤残基催化的。

[终译]生命起源时,RNA世界学说把 RNA 放在中心位置。核糖体是核酶的观察结果支持了 RNA世界学说的观点: 核糖体的催化位点是由 RNA 组成的,蛋白质没有主要的结构作用,具有次要的功能重要性。这一点在2001年核糖体三维结构的破译中得到了证实。具体来说,肽键的形成,即将氨基酸结合成蛋白质的反应,现在已知是由 rna 中的腺嘌呤残基催化的。

RNAs are known to play roles in other cellular catalytic processes, specifically in the targeting of enzymes to specific RNA sequences. In eukaryotes, the processing of pre-mRNA and RNA editing take place at sites determined by the base pairing between the target RNA and RNA constituents of small nuclear ribonucleoproteins (snRNPs). Such enzyme targeting is also responsible for gene down regulation through RNA interference (RNAi), where an enzyme-associated guide RNA targets specific mRNA for selective destruction. Likewise, in eukaryotes the maintenance of telomeres involves copying of an RNA template that is a constituent part of the telomerase ribonucleoprotein enzyme. Another cellular organelle, the vault, includes a ribonucleoprotein component, although the function of this organelle remains to be elucidated.

RNAs are known to play roles in other cellular catalytic processes, specifically in the targeting of enzymes to specific RNA sequences. In eukaryotes, the processing of pre-mRNA and RNA editing take place at sites determined by the base pairing between the target RNA and RNA constituents of small nuclear ribonucleoproteins (snRNPs). Such enzyme targeting is also responsible for gene down regulation through RNA interference (RNAi), where an enzyme-associated guide RNA targets specific mRNA for selective destruction. Likewise, in eukaryotes the maintenance of telomeres involves copying of an RNA template that is a constituent part of the telomerase ribonucleoprotein enzyme. Another cellular organelle, the vault, includes a ribonucleoprotein component, although the function of this organelle remains to be elucidated.

已知 RNA 在其他细胞催化过程中发挥作用,特别是在酶靶向特定的 RNA 序列。在真核生物中,前 mrna 和 RNA 编辑的过程发生在目标 RNA 和小核核糖核蛋白(snRNPs)的 RNA 成分之间的碱基配对决定的位点。这种酶的靶向作用也是通过 RNA 干扰(RNAi)来调节基因的下调,在 RNA 干扰中,一种酶相关的引导 RNA 针对特定的 mRNA 进行选择性破坏。同样,在真核生物中,端粒的维持涉及到 RNA 模板的复制,而 RNA 模板是端粒酶核糖核蛋白的组成部分。另一个细胞器,穹隆,包括一个核糖核蛋白组件,虽然这个细胞器的功能仍有待阐明。

[终译]已知 RNA 在其他细胞催化过程中发挥作用,特别是在酶靶向特定的 RNA 序列。在真核生物中,前 mrna 和 RNA 编辑的过程发生在目标 RNA 和小核核糖核蛋白(snRNPs)的 RNA 成分之间的碱基配对决定的位点。这种酶的靶向作用也是通过 RNA 干扰(RNAi)来调节基因的下调,在 RNA 干扰中,一种酶相关的引导 RNA 针对特定的 mRNA 进行选择性破坏。同样,在真核生物中,端粒的维持涉及到 RNA 模板的复制,而 RNA 模板是端粒酶核糖核蛋白的组成部分。另一个细胞器,穹隆,包括一个核糖核蛋白组件,虽然这个细胞器的功能仍有待阐明。

See also

  • GADV-protein world hypothesis
  • The Major Transitions in Evolution
  • RNA-based evolution
  • Protocell or Pre-cell, the primordial version of a cell which confined RNA and later, DNA

[终译]

GADV-蛋白质世界假说

进化中的重大转变

基于RNA的进化

原始细胞或前细胞——细胞的原始形式,影响RNA和后来的DNA

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Further reading


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External links

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模板:Origin of life 模板:Molecules detected in outer space 模板:Self-replicating organic structures

Category:Biological hypotheses Category:Origin of life Category:Prebiotic chemistry Category:RNA Category:1962 in biology

类别: 生物学假说类别: 生命起源类别: 生命起源前化学类别: RNA 类别: 1962年生物学


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