章节大纲

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    How do you go from four nucleotide letters to 20 amino acids?
    ::你如何从4个核酸字母 到20个氨基酸?

    You need a code. And the code that changes the information embedded in and into ordered amino acids and is the genetic code. And every living organism uses the same genetic code.
    ::你需要一个代码。这个代码可以改变 嵌入和嵌入有顺序的氨基酸的信息 并且是基因代码。每个生物都使用相同的遗传代码。

    The Genetic Code
    ::《遗传法》

    So how exactly is the language of nucleotides used to code for the language of amino acids? How can a code of only As, Cs, Gs, and Us carry information for 20 different amino acids? The genetic code is the code in which the language of nucleotides is used to create the language of amino acids.
    ::核核糖酸的语言是如何用于对氨基酸语言进行编码的?只有A类、C类、G类和U类的代码怎么可能含有20种不同的氨基酸的信息?基因代码是使用核酸语言来创造氨基酸语言的代码。

    Cracking the Code
    ::破坏《守则》

    A code of at least three letters has to be the answer. A one letter code would only be able to code for four amino acids. A two letter code could only code for 16 amino acids. With a three letter code, there are 64 possibilities. As there are 20 amino acids, the code must consist of at least three letters.
    ::答案必须是至少三个字母的代码。 一个字母代码只能对四个氨基酸进行编码。 两个字母代码只能对16个氨基酸进行编码。 有3个字母代码,就有64种可能性。因为有20个氨基酸,该代码必须由至少三个字母组成。

    In 1961, Francis Crick and Sydney Brenner demonstrated the presence of codons , that is, three bases of RNA that code for one amino acid ( Figure ). Also in 1961, Marshall Nirenberg and Heinrich Matthaei at the National Institutes of Health (NIH) demonstrated that a poly(U) RNA sequence was translated into a polypeptide consisting of only the amino acid phenylalanine. This proved that the codon UUU coded for the amino acid phenylalanine. Extending this work, Nirenberg and his coworkers were able to determine the nucleotide makeup of 54 of the 64 codons. Others determined the remainder of the genetic code ( Figure ). 
    ::1961年,Francis Crick和Sydney Brenner展示了一种氨酸(Figure)的代号,即RNA的三个基点。 1961年,国家卫生研究所的Marshall Nirenberg和Heinrich Matthaei也证明,一种聚(U)RNA序列被转化成一种只由氨酸苯丙烯组成的聚苯二烯组成的聚苯二烯;这证明氨酸苯丙烯的codon UU编码。 Nirenberg及其同事在延长这项工作后,能够确定64个codon中54个的核酸构成。 其他人确定了遗传法的其余部分(Figure )。

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    The mRNA is divided into three-base segments called codons. A codon is the segment of nucleotides that codes for an amino acid, or for a start or stop signal. There are 64 codons.
    ::MRNA分为三个基段,称为codons。一个codon是核糖核酸的一部分,它编码为氨基酸或起始或停止信号。有64个codon。

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    The Genetic Code. The Genetic Code: Codons are in the mRNA sequence. The three letter and one letter code for the amino acids are shown. To read the code, find the first base on the left, the second base at the top, and the third base in the center of the table. For example, the codon GGG codes for the amino acid glycine (as does GGC, GGA, and GGU), CCG codes for Proline, UUA codes for Leucine, and AAG codes for Lysine. There are 64 codons that code for 20 amino acids and three stop codons, so an amino acid may have more than one corresponding codon.
    ::《遗传法》。《遗传法》:Codons在 mRNA 序列中。显示的是氨基酸的三字母和一个字母代码。要阅读代码,请在左边找到第一个基点,在顶部找到第二个基点,在表中央找到第三个基点。例如,氨基酸甘油的codon GGGG代码(如GGC、GGA和GGUU)、Proline的CCG代码、Leucine的UA代码和Lysine的AAAG代码。有64个Condon,该代码用于20个氨基酸和3个停止的焦炭,因此氨基酸可能有不止一个相应的codon。

    Start and Stop Codons
    ::开始并停止 Codons

    The codon AUG codes for the amino acid methionine. This codon is also the start codon which begins every of every amino acid chain. The translational machinery “reads” the mRNA base by base until a AUG start codon is identified. The mRNA is then translated codon by codon until it reaches a stop codon . Stop codons are not associated with a tRNA or amino acid and signal the end of translation. There are three stop codons: UAG, UGA, UAA. Stop codons are also known as termination codons.
    ::氨基酸甲硫磷的codon AUG编码。 这个codon 也是开始每一个氨基酸链的开始codon。 翻译机器按基数“ 读” mRNA基数直到确定一个 AUG 启动codon 。 然后, mRNA 以codon 翻译 Codon ,直到达到 停止 codon 。 停止 codon 与 tRNA 或 氨基酸 无关, 并信号翻译结束 。 有三种停止 codon : UAG、 UGA、 UAA。 停止 Codon 也被称为终止 Codon 。

    The Reading Frame
    ::阅读框架

    The reading frame is the frame of three bases in which the mRNA is read and translated. Every sequence can be read in three reading frames, each of which will produce a different amino acid sequence. For example, in the sequence GCAUGGGGGUCUAG, the reading frame can begin with either the first G, the first C, or the first A. As stated above, translation starts with the start codon which consists of the three bases AUG. Each subsequent codon is translated until an "in-frame" stop codon is reached. In the example above, the polypeptide sequence would be: methionine – glycine – valine – stop.
    ::读取框架是读和翻译 mRNA 的三个基础的框。 每个序列都可以在三个阅读框中读取,每个序列将产生不同的氨基酸序列。 比如,在 GCAUGGGGGUUAG的序列中,读框可以从第一个G、第一个C或第一个A开始。 如上所述,翻译从三个基础AUG组成的开始的codon开始。 每一个随后的codon都会被翻译到“ 框架内” 停止 codon 达到为止。 在以上的例子中, 聚苯丙胺序列将是: 甲基苯丙胺 — 甘油 — valine — 停止。

    that disrupt the reading frame by insertions or deletions of a non-multiple of 3 nucleotide bases are known as frameshift mutations . Take the example THEBIGFATCATATETHEREDRAT.
    ::通过插入或删除3个核酸基数的非倍数而破坏读数框架的,称为轮廓变异。 以TebGATATATTEDEREDRAT为例。

    Broken into codons, this example would be easily read as: THE BIG FAT CAT ATE THE RED RAT.
    ::这个例子可以很容易地被解读为:

    However, a deletion mutation that disrupts the reading frame, results in a message that does not make any sense.
    ::然而,删除会扰乱阅读框架的突变,导致一种没有任何意义的信息。

    If the ‘B’ is deleted: THE IGF ATC ATA TET HER EDR AT.
    ::如果删除了`B ' :IFA ATC ATA 将她的EDR AT。

    Once the reading frame is disrupted, the mRNA may not be translated properly. Different amino acids would be inserted into the protein. These mutations may impair the function of the resulting protein, if the protein is even formed. Many frameshift mutations result in a premature stop codon, in other words, a stop codon that come earlier than normal during translation. This would result in a smaller protein, most likely without normal function. Keep in mind that not all mutations are harmful; some are beneficial. Evolution would not occur without these beneficial mutations .
    ::一旦读取框架中断, mRNA 可能不会被正确翻译。 不同的氨基酸将被插入蛋白质中。 这些突变可能会影响由此产生的蛋白质的功能, 如果蛋白甚至形成的话。 许多框架变异导致过早停止的codon , 换句话说, 在翻译过程中, 停止的codon 早于正常状态。 这将导致一个较小的蛋白质, 很可能没有正常功能 。 记住并非所有的突变都是有害的; 有些是有利的。 没有这些有益的突变, 进不会发生 。

    The Wobble Hypothesis
    ::摇摆的假说

    In 1966, Francis Crick proposed the Wobble Hypothesis which explained that the degeneracy of the genetic code is caused by the structure of the anticodon of tRNA. The anticodon is a three base sequence on the tRNA complementary to the codon on the mRNA. Each tRNA binds to a specific amino acid, but the anticodons of some tRNA molecules can bind to two or three different codons. This flexibility of the anticodon is caused by the less stringent 5' base on the anticodon loop, also referred to as the wobble base, which binds to the 3' base on the mRNA. Only the first two nucleotides are stringent and spatially confined for the decoding of the mRNA codon into an amino acid. This explains why degenerate codons often differ in the third position, as depicted in Figure . For example, the amino acid alanine is coded by codons GCU, GCC, GCA and GCG. The wobble movement of the base in the 5' anticodon position is necessary for this degenerate capability.
    ::1966年,Francis Crick提议了Wobble假肢,其中解释说,基因编码的变异性是由tRNA抗codon结构造成的。抗codon是tRNA补充 mRNA上codon的tRNA的三个基序。每个tRNA都与特定的氨酸结合,但一些tRNA分子的抗codon可以与两个或三个不同的codon结合。抗codon的这种灵活性是由抗codon环上较松松的5英尺基(也称为Wobbble基)造成的,该基与MRNA上3的基连接。只有头两根核酸对于将 mRNAcodon分解为氨基酸来说是严格和空间限制的。这就是为什么腐蚀性codon在第三个位置上常常有所不同的原因,如图所示。例如,氨酸alanine是由GCU、GCA、GCA和GCGG的codon调制成的基。这种基在5'cod的必要位置上,这种基质运动在5'coddon的能力是这个必要的。

    The Wobble Hypothesis states that rules of are relaxed at the third position, so that a base can pair with more than one complementary base. The hypothesis explains why the base inosine is included in position 1 in the anticodons of various tRNAs, why many mRNA codon words translate to a single amino acid, why there are appreciably fewer tRNAs than mRNA codon types and why the redundant nature of the genetic code translates into a precise set of 20 amino acids.
    ::Wobble假说道,第三种位置的规则是宽松的,这样一个基座可以配对一个以上的补充基座。 假设解释了为什么碱性因子因子因子因子在各种tRNA的抗codon中被列入第1位,为什么许多 mRNA Codon 的词会转化成一种单一的氨酸,为什么tRNA 明显少于 mRNA codon 类型,为什么遗传编码的多余性质会转化为一套精确的20 氨酸。

    A wobble base pair is a non-Watson Crick base pairing between two nucleotides in RNA molecules. The four main wobble base pairs are guanine-uracil, inocine-uracil, inosine-adenine, and inosine-cytosine. Wobble base pairs are fundamental in RNA secondary structure and are critical for the proper translation of the genetic code. Inosine is a nucleoside that is formed from the hydrolytic deamination of adenine. Structurally, it resembles guanine, but lacks the 2-amino group. This lack of the 2-amino group allows inosine to form base pairs with uracil, cytosine and adenine, making it a particularly wobbly base.
    ::Wobble基底配对是非Watson Crick基底,配对于RNA分子中的两颗核核素。四种主要核素基底配对是:guanine-uracil、nocine-uracil、Inosine-adinen和Inosine-cytosine。Wobble基底配对是RNA二级结构的基础,对于基因代码的适当翻译至关重要。Inosine是一个核素边,它是由的水解脱酸形成的。在结构上,它类似于guanine,但缺乏2-mino基组。由于缺少2-mino基组,所以Inosine可以组成有urcil、cytosine和adenine的基底对,因此它特别是一个交织的基底。

    Degeneracy of the Universal Genetic Code
    ::《世界遗传法》的减损

    When there are 64 codon combinations for 20 amino acids (and stop codons), there is going to be some overlap. Within the genetic code there is redundancy but no ambiguity. For example, the codons GGG, GGA, GGC, and GGU all encode the amino acid glycine, but none encode another amino acid. Degenerate codons often differ in the third position.
    ::当20种氨基酸(和停止冷冻的酸)有64种CODon组合时,就会有一些重叠。 在遗传代码中,存在冗余,但没有模糊之处。 比如,CODons GGG、GGA、GGC和GGU都编码了氨基酸甘油,但没有一种编码又一种氨基酸。 第三种状态的脱氧钴通常不同。

    The genetic code is said to be universal. That is, the same code is utilized by the simplest prokaryotic organism and by humans. This universality is a tremendous benefit to mankind. If a human gene is placed in a , it looks just like a piece of DNA to the bacteria. The human As, Cs, Gs, and Ts look just like the bacteria’s As, Cs, Gs, and Ts. So, the bacterial proteins will transcribe and translate this DNA, making a human protein.
    ::基因代码据说是普遍性的。也就是说,同样的代码被最简单的蛋白质生物和人类使用。这个普遍性是人类的巨大好处。如果人类基因被放置在一个基因中,细菌的DNA看起来就像一个DNA。人类的A、C、G和T看起来就像细菌的A、C、G和T。因此,细菌蛋白质将进行转录和翻译,制造人类蛋白质。

    But how exactly are these proteins made? We have been referring to mRNAs, tRNAs, , codons the genetic code and and translation throughout the concepts. How do they all come together to make a protein? Through translation.
    ::但是这些蛋白质是如何生产的呢?我们一直提到 mRNAs, tRNAs, atRNAs, CCONs 遗传代码, 并在整个概念中翻译。它们是如何聚集在一起制造蛋白质的? 通过翻译。

     

     

    Summary
    ::摘要

    • The genetic code consists of the sequence of bases in DNA or RNA.
      ::遗传代码包括DNA或RNA中基数的顺序。
    • Groups of three bases form codons, and each codon stands for one amino acid (or start or stop).
      ::3个基底组构成codon, 每个codon代表一种氨基酸( 开始或停止) 。
    • Start and stop codons signal the beginning and end of translation; the codons are read in sequence following the start codon until a stop codon is reached.
      ::开始并停止 codons 表示翻译的开始和结束; codons 是在启动 codon 之后按顺序读取, 直到达到一个停止 codon 。
    • The reading frame is the frame of three bases in which the mRNA is read.
      ::读取框架是读取 mRNA 的三个基底的框。
    • The genetic code is universal, unambiguous, and redundant.
      ::遗传法是普遍、明确和多余的。

    Review
    ::回顾

    1. What is the genetic code? What are codons?
      ::遗传密码是什么?
    2. Describe the role of the Genetic Code in translation.
      ::说明《遗传法》在翻译方面的作用。
    3. What is a reading frame?
      ::什么是阅读框架?
    4. Use the genetic code to translate the following segment of RNA into a sequence of five amino acids: GUC-GCG-CAU-AGC-AAG.
      ::使用遗传编码将RNA的以下部分转化为五种氨基酸的序列:GUC-GCG-CAU-AGC-AAG。
    5. The genetic code is universal, unambiguous, and redundant. Explain what this means and why it is important.
      ::基因代码是普遍、明确和多余的。 请解释这意味着什么以及为什么它很重要。