Section outline

  • A blue spiral staircase winding around a central axis inside a brightly lit room.

    Did you ever see a spiral staircase like the one in the opening image? The steps connect the two sides of the staircase, which winds around a central axis. A spiral staircase can be used as a model for a DNA molecule . DNA is a nucleic acid.
    ::你曾经见过像开张图像中那样的螺旋楼梯吗? 阶梯连接了中央轴周围的阶梯两侧。 螺旋楼梯可以用作DNA分子的模型。 DNA是一种核酸。

    Q: DNA is such a well-known molecule that you probably know something about it already. What do you know about DNA, and why do you think this molecule is so “famous”?
    ::问题:DNA是这样一个众所周知的分子,你可能已经知道它。你对DNA了解多少,你为什么认为这个分子如此“臭名昭著 ” ?

    A: You many know that DNA contains genes. It is so “famous” because it explains how we inherit traits from our parents and pass them on to our offspring.
    ::甲:你们许多人都知道DNA含有基因。它是如此“有名”,因为它解释了我们如何继承父母的特质,并将这些特质传给后代。

    What Are Nucleic Acids?
    ::什么是核酸?

    Nucleic acids are one of four classes of . (The other three classes are , , and .) Nucleic acids include RNA (ribonucleic acid) as well as DNA (deoxyribonucleic acid). Both types of nucleic acids contain the carbon, hydrogen, oxygen, nitrogen, and phosphorus. 
    ::核酸是四类.(其他三类是,和.)核酸包括RNA(核糖核酸)和DNA(脱氧核糖核酸),两种核酸都含有碳、氢、氧、氮和磷。

    Q: Which of the elements in DNA is not identified with any other class of biochemical compounds?
    ::问题:脱氧核糖核酸中哪些元素未与任何其他种类的生化化合物识别?

    A: All biochemical compounds contain carbon, hydrogen, and oxygen; and proteins as well as nucleic acids contain nitrogen. Phosphorus is the only element that is identified with nucleic acids.
    ::A:所有生化化合物都含有碳、氢和氧;蛋白质以及核酸含有氮。

    Nucleotides
    ::核分子

    Nucleic acids consist of chains of small molecules called nucleotides, which are held together by . The structure of a nucleotide is shown in the Figure . Each nucleotide consists of:
    ::核酸由小分子链组成,称为核糖核酸,由核糖核酸合在一起。 核酸的结构在图中显示。 每一种核酸包括:

    1. a phosphate group, which contains phosphorus and oxygen (PO 4 ).
      ::a 磷酸盐组,含有磷和氧(PO4)。
    2. a sugar, which is deoxyribose (C 5 H 8 O 4 ) in DNA and ribose (C 5 H 10 O 5 ) in RNA.
      ::a 糖,在RNA的DNA和肋骨(C5H10O5)中为脱氧核糖(C5H8O4)。
    3. one of four nitrogen-containing bases. (A is a that is not neither acidic nor neutral.) In DNA, the bases are adenine, thymine, guanine, and cytosine. RNA has the base uracil instead of thymine, but the other three bases are the same.
      ::4个含氮基座之一。 (A既不是酸性的,也不是中性的。 )在DNA中,这些基座是、胸腺、guanine 和 cytosine。 RNA 的底座是毫氨,而不是胸腺,但其他3个基座是一样的。

    A nucleotide's components: phosphate group, deoxyribose sugar, and nitrogenous base.

    The Double Helix
    ::双螺旋

    RNA consists of just one chain of nucleotides. DNA consists of two chains. Nitrogen bases on the two chains of DNA form with each other. Hydrogen bonds are relatively weak bonds that form between a positively charged hydrogen in one molecule and a negatively charged atom in another molecule. Hydrogen bonds form only between adenine and thymine, and between guanine and cytosine. These bonds hold the two chains together and give DNA is characteristic double helix, or spiral, shape.
    ::RNA仅由一串核糖核酸组成。DNA由两串链组成。两个DNA链的氮基是两个DNA链的,而两个DNA链的氮基是彼此的。氢的结合是相对薄弱的,一个分子中正充电的氢与另一个分子中负充电的原子之间形成联系。氢的结合只存在于denine和Homine之间以及guanine和cytosine之间。这些联系将两个链连接在一起,给予DNA的特征是双螺旋或螺旋形状。

    You can see the shape of the DNA molecule in the Figure . Sugars and phosphate groups form the “backbone” of each chain of DNA. The bonded bases are called base pairs. Determining the structure of DNA was a huge scientific breakthrough.
    ::您可以在图中看到DNA分子的形状。糖和磷酸盐组构成每个DNA链的“背骨 ” 。 连接基座被称为基底对。 确定DNA的结构是一个巨大的科学突破。

    DNA structure showing double helix and color-coded base pairs.

    Q: Compare the structure of DNA to a spiral staircase. What part of the molecule do the stair steps represent?
    ::问题:将DNA结构与螺旋阶梯作比较。该阶梯代表分子的哪一部分?

    A: The steps represent the base pairs.
    ::A:步骤代表基本对子。

    Functions of Nucleic Acids
    ::核酸的功能

    DNA stores genetic information in the cells of all living things. It contains the genetic code. This is the code that instructs cells how to make proteins. The instructions are encoded in the sequence of nitrogen bases in the nucleotide chains of DNA. RNA copies and interprets the genetic code in DNA and is also involved in the synthesis of proteins based on the code. 
    ::DNA在所有生物细胞中储存基因信息。 它包含基因代码。 这是指导细胞如何制造蛋白质的代码。 指令在DNA核糖核酸链中的氮基序列中编码。 RNA 复制并解释DNA中的基因代码, 并参与根据该代码合成蛋白质。

     

     

     

     

     

    Q: DNA is found only in the nucleus of cells, but proteins are synthesized in the cytoplasm of cells, outside of the nucleus. How do you think the instructions encoded in DNA reach the cytoplasm so they can be used to make proteins?
    ::问题:DNA只存在于细胞核心中,但蛋白质在细胞细胞的细胞细胞图层中合成,在细胞核心之外。你认为DNA编码的指示如何到达细胞图层,以便用来制造蛋白质?

    A: After RNA copies the instructions in DNA, it carries them from the nucleus to a site of protein synthesis in the cytoplasm, where the instructions are translated into a protein.
    ::A:在RNA复制了DNA中的指示之后,它将这些指示从核转移到细胞托盘中的蛋白合成点,将指示转化为蛋白质。

    Summary
    ::摘要

    • Nucleic acids are one of four classes of biochemical molecules. Nucleic acids include RNA (ribonucleic acid) and DNA (deoxyribonucleic acid).
      ::核酸是四类生物化学分子之一,包括RNA(核糖核酸)和DNA(脱氧核糖核酸)。
    • Nucleic acids consist of chains of small molecules called nucleotides, which are held together by covalent bonds.
      ::核酸由称为核酸的小型分子链组成,这些分子链由共价联结保持在一起。
    • RNA is made of one nucleotide chain, and DNA is made of two. The two chains of DNA are held together by hydrogen bonds in the shape of a double helix.
      ::RNA是由一个核糖核酸链组成的,DNA是由两个DNA链组成的。两种DNA链由氢链以双螺旋形的氢系在一起。
    • DNA contains the genetic code, which instructs cells how to make proteins. RNA copies the genetic code in DNA and helps synthesize proteins based on the code.
      ::DNA包含基因代码,它指导细胞如何制造蛋白质。 RNA复制DNA中的遗传代码,并帮助根据该代码合成蛋白质。

    Review
    ::回顾

    1. What are nucleic acids? What are the two types of nucleic acids?
      ::什么是核酸?两种核酸是什么?
    2. Describe the structure of a nucleotide.
      ::描述核糖核酸的结构。
    3. What holds nucleotides together in a nucleic acid?
      ::在核酸中,什么把核糖核酸的核酸结合在一起?
    4. Compare and contrast the structure and functions of DNA and RNA. 
      ::比较和比较DNA和RNA的结构和功能。