章节大纲

  • 常规

    全部折叠 展开全部

  • DNA 结构和复制

    What you will learn
    ::你会学到什么

    • Structure and function of
      ::结构和职能
    • Chargaff's rule
      ::资产规则
    • DNA replication and the role of DNA polymerase
      ::DNA复制和DNA聚合酶的作用

    What does DNA look like?
    ::DNA长什么样?

    DNA is a double helix
    DNA is a double helix

    Have you ever seen a ladder? Imagine being able to twist the ladder. The basic shape of DNA is sometimes described as a twisted ladder. Do you see the resemblance? Which parts of the DNA molecule are like the steps of the ladder? What about the railings? There are other ways you can represent or model the structure of DNA in order to better understand its function. The discovery of DNA’s structure actually involved modeling. A model is a very useful tool in science . Models provide a way to explore things that might be too complex or small to investigate directly. So how might you create a model of DNA?
    ::你见过梯子吗? 想象一下能够扭曲梯子。 DNA的基本形状有时被描述为一个扭曲的梯子。 你是否看到相似之处? DNA分子的哪个部分像梯子的阶梯? 栏杆呢? 是否有其他方法可以代表或模拟DNA的结构, 以便更好地了解其功能。 DNA结构的发现实际上涉及到模型的建模。 模型是科学中非常有用的工具。 模型提供了一种探索可能太复杂或太小而无法直接调查的东西的方法。 那么如何创建DNA模型呢?

    DNA Structure
    ::DNA结构

    Chargaff's Rules
    ::资产规则

    Other important discoveries about DNA were made in the mid-1900s by Erwin Chargaff. He studied DNA from many different . He was especially interested in the four different nitrogen bases of DNA: adenine (A) , guanine (G) , cytosine (C) , and thymine (T) .
    ::Erwin Dhoffaff在19世纪中叶发现了关于DNA的其他重要发现。他研究了许多不同的DNA。他对DNA的四个不同的氮基(adenine (A)、guanine (G)、cytosine (C) 和 Youmine (T))特别感兴趣。

    Chargaff found that concentrations of the four bases differed from one species to another. However, within each species, the concentration of adenine was always about the same as the concentration of thymine . The same was true of the concentrations of guanine and cytosine . These observations came to be known as Chargaff’s rules . The significance of the rules would not be revealed until the structure of DNA was discovered.
    ::脑电图发现,四个基点的浓度因物种而异。 然而,在每种物种中,的浓度总是与甲状腺的浓度相同。 谷氨和细胞素的浓度也是如此。 这些观察结果被称为“阿扎夫规则 ” 。 在发现DNA结构之前,规则的意义是不会暴露的。

    DID YOU KNOW?
    The same nitrogen base adenine present in DNA is also found in adenosine triphosphate (ATP), an energy-carrying molecule that use to power their cellular and metabolic processes.
     

     

    The Double Helix
    ::双螺旋

    After DNA was found to be the genetic material , scientists wanted to learn more about it. James Watson and Francis Crick are usually given credit for discovering that DNA has a double helix shape, like a twisted ladder. 
    ::在发现DNA是遗传物质后,科学家们想了解更多这方面的信息。 詹姆斯·沃森和弗朗西斯·克里克发现DNA有双螺旋形,像扭曲的梯子。

    The discovery was based on the prior work of Rosalind Franklin and other scientists, who had used X-rays to learn more about DNA’s structure. Franklin and these other scientists have not always been given credit for their contributions. With the help of prior work from other scientists, Watson and Crick developed a model of the DNA double helix structure that correctly matched what was observed in Franklin’s X-ray crystallography photos.
    ::这一发现基于Rosalind Franklin和其他科学家先前的工作,他们用X光片了解更多DNA结构。 富兰克林和其他科学家的贡献并不总是得到肯定。 在其他科学家的帮助下,华生和克瑞克开发了DNA双螺旋结构模型,该模型与富兰克林X光晶体学照片中所观察到的完全吻合。

     

     

     

     

    The double helix shape of DNA, together with Chargaff’s rules, led to a better understanding of DNA. DNA, as a , is made from nucleotide monomers , and the DNA double helix consists of two polynucleotide chains . Each nucleotide consists of a sugar (deoxyribose) , a phosphate group , and a nitrogen-containing base (A, C, G, or T).
    ::DNA的双螺旋形状,加上阿卡夫的规则,导致人们更好地了解了DNA。 DNA作为一个DNA,是由核酸单体组成的,而DNA的双螺旋由两条多核酸链组成。 每一种核酸由糖(deoxyribose ) 、 磷酸盐组和含氮基(A、C、G或T)组成。

    Scientists concluded that bonds (hydrogen bonds) between complementary bases hold together the two polynucleotide chains of DNA. Adenine always bonds with its complementary base, thymine. Cytosine always bonds with its complementary base, guanine. If you look at the nitrogen bases in the figure above, you will see why. Adenine and guanine have a two-ring structure. Cytosine and thymine have just one ring. If adenine were to bind with guanine and cytosine with thymine, the distance between the two DNA chains would be variable. However, when a one-ring molecule binds with a two-ring molecule, the distance between the two chains is kept constant. This maintains the uniform shape of the DNA double helix. These base pairs (A-T or G-C) stick into the middle of the double helix, forming, in essence, the steps of the twisted ladder.


    ::科学家得出结论, 补充基点之间的债券( 氢环) 将DNA的两个多核酸链连接在一起。 亚丁总是与补充基点( 甲状腺) 紧密联系。 赛托辛总是与补充基点( guanine ) 紧密联系。 如果您在上图中看到氮基( guanine ) , 你就会明白原因 。 亚丁 和 guanine 有着双环结构。 赛托辛 和 甲状腺只有一个环环。 如果亚丁 与 guanine 和 cytosine 连接在一起, 两个DNA 链条的距离就会变异。 但是, 当一环分子与两环分子结合时, 两个链条的距离会保持不变 。 这保持了DNA双螺旋的统一形状 。 这些基对( A- T 或 G- C) 将双螺旋夹在双螺旋的中间, 实质上形成扭曲梯子的步伐 。

    CAn you Build?

    Try to bond the nitrogen bases on the right, with the complementary base. Start by dragging the nitrogen bases on the right.
    ::尝试将右边的氮基与补充基连接起来。 开始将右边的氮基拖到右边 。

     

     

    DNA Replication
    ::DNA复制

    Knowledge of DNA’s structure helped scientists understand how DNA replicates. DNA replication is the process in which DNA is copied. It occurs during the synthesis (S) phase of the eukaryotic cell cycle.
    ::对DNA结构的了解有助于科学家了解DNA是如何复制的。 DNA复制是DNA复制的过程。 它发生在尿液细胞循环合成(S)阶段。

    Illustration of based on images from David S. Goodsell and the RCSB PDB under a CC-BY-4.0 license. Original image: https://pdb101.rcsb.org/motm/168 and https://pdb101.rcsb.org/motm/3.
    ::以David S. Goodsell和RCSB PDB的图像为基础,根据CC-BY-4.0许可使用。原始图像:https://pdb101.rcsb.org/motm/168和https://pdb101.rcsb.org/motm/3。

    DNA replication begins when an enzyme, DNA helicase, breaks the bonds between complementary bases in DNA. This exposes the bases inside the molecule so they can be “read” by another enzyme, DNA polymerase, and used to build two new DNA strands with complementary bases, also by DNA polymerase. The two daughter molecules that result each contain one strand from the parent molecule and one new strand that is complementary to it. As a result, the two daughter molecules are identical to the parent molecule. DNA replication is a semi-conservative process because half of the parent DNA molecule is conserved in each of the two daughter DNA molecules.
    ::DNA复制始于酶, DNA helicase, 打破DNA中互补基点之间的连接。 这暴露了分子内部的基点, 这样它们就可以被另一个酶, DNA聚合酶“ ” 读取, 并用来在补充基点上建立两条新的DNA线, DNA聚合酶也是如此。 产生两个女分子的每条母分子都含有母分子的一丝, 和与之互补的一条新线。 因此, 两个女分子与母分子是相同的。 DNA复制是一个半保守过程, 因为母DNA分子的一半在两个女分子中保存。

    DID YOU KNOW?
    DNA polymerase has the remarkable ability to proofread and correct its own mistakes. If it incorporates the wrong base at any point, it corrects itself immediately and only then proceeds with the replication process.
     

     

     

     

     

     

    Summary
    ::摘要

    • Chargaff's rules state that the amount of A is similar to the amount of T, and the amount of G is similar to the amount of C.
      ::教职员工的细则规定,A的金额与T的金额类似,G的金额与C的金额类似。
    • Watson and Crick discovered that DNA has a double helix shape, consisting of two polynucleotide chains held together by bonds between complementary bases.
      ::Watson和Crick发现DNA具有双螺旋形状,由两个圆核酸链组成,由互补基地之间的纽带连接在一起。
    • DNA replication is semi-conservative: half of the parent DNA molecule is conserved in each of the two daughter DNA molecules.
      ::DNA的复制是半保守性的:母DNA分子的一半保存在两个女儿的DNA分子中。

    Review
    ::回顾

    1. What are Chargaff’s rules?
      ::教官的规则是什么?
    2. Identify the structure of the DNA molecule.
      ::识别DNA分子的结构。
    3. What are nucleotides? What makes up a nucleotide?
      ::核糖核酸是什么 核酸是什么
    4. Why is DNA replication said to be semi-conservative?
      ::为什么DNA复制据说是半保守性的?
    5. Create a diagram that shows how DNA replication occurs.
      ::创建显示如何复制DNA的图表 。
    6. What is complementary base pairing? Explain why complementary base pairing is necessary to maintain the double helix shape of the DNA molecule.
      ::什么是互补基配对?解释为什么补充基配对对于保持DNA分子的双螺旋形状是必要的。