英汉对照分子生物学导论 教学课件 ppt 作者 [美]西尔维恩 W.勒潘 王勇 编著Chapter 2.ppt

Nucleotides are polymerized to form nucleic acids. If deoxy-ribonucleotides are used, the polymer is called deoxyribonucleic acid, or DNA. If ribonucleotides are used, the polymer is called ribonucleic acid, RNA. 核苷酸聚合起来产生的就是核酸。如果使用的是脱氧核糖核苷酸，产生的聚合物是脱氧核糖核酸，简称为DNA。如果使用的是核糖核苷酸，产生的聚合物是核糖核酸，简称为RNA。 When nucleotides are polymerized, the triphosphate group of one nucleotide reacts with the 3’-OH (hydroxyl) group of another nucleotide. In this reaction, two phosphates are removed from one nucleotide, and the two nucleotides are connected by phosphodiester bonds. 当核苷酸发生聚合的时候，一个核苷酸的三磷酸基团与另一个核苷酸的3’-OH（羟基）发生反应。在这一反应中，两个磷酸基团从一个核苷酸上移去，之后两个核苷酸由留下的单磷酸连接在一起，形成的键叫做磷酸二酯键。 Like peptides, the nucleic acid polymer is linear, meaning it has no branches. On one end of the polymer is the 3’-OH group of a nucleotide. This end is called the three prime end. On the other end is a 5’-triphosphate group of a different nucleotide. That is called the five prime end. 与肽一样，核酸聚合物是线性的，意味着它没有分支。在聚合物的一个末端是3’-OH。这一末端叫做三一撇末端，写成3’末端。另一个末端是另一个核苷酸的5’-三磷酸基团。这一末端叫做五一撇末端，写成5’末端。 Between the two ends of the DNA is a simple, repeating structure of sugars connected by phosphodiester bonds. This structure is called the sugar-phosphate backbone. 在两个末端之间DNA是简单的、重复的由磷酸二酯键连接起来的糖。这种结构被叫做糖-磷酸骨架。 Now, let’s take a look at the structure of DNA. Generally, DNA is in double-stranded state. The two strands are held together by hydrogen bonds between their bases. 现在，让我们来看一看DNA的结构。一般来说，DNA是以双链形式存在的，两条链由它们碱基之间的氢键保持在一起。 In a double-stranded DNA, hydrogen bonds are formed between adenine on one strand and thymine on the other, or between guanine on one strand and cytosine on the other. Bases that can correctly bond to each other are said to be complementary. The two hydrogen bonded nucleotides, each one located on a different strand, is called a base pair. A-T base pairs are connected by two hydrogen bonds. G-C base pairs are connected by three hydrogen bonds. 在双链DNA分子中，氢键在一条链的腺嘌呤和另一条链的胸腺嘧啶之间、或一条链的鸟嘌呤和另一条链的胞嘧啶之间形