大学生物专业英语lesson_five.pptVIP

* * 2 the search for chemistry and molecularstructure of nucleic acids * * Nuclei acid, originally isolated by Johann Miescher in 1871, was identified as prime constituent of chromosomes through the use of the red-staining method developed by Feulgen in the early 1900s. 在1871年，核酸最初是由Johann Miescher（约翰拿·米歇尔 瑞士化学家）分离成功的，并通过应用1900年由Feulgen（福尔根 ） 发现的R带技术被证实是染色体组最基本的组成。 * * 　　Frederick Griffith′s experiments with the R and S stains of pneumococci [nju:m?k?ksa?] showed that an as yet unknown material from one set of bacterial could alter the physical traits of a second set. 　　Frederick Griffith（弗雷德里克·格里菲斯 ）对粗糙和光滑的肺炎球菌实验表明，来自一组细菌的某种未知物质可以改变另一组细菌的物理性状。 * * 　　In the 1940s the team of Avery, MacLeod, and McCarty showed that this unknown material was DNA. 　　在1940年， Avery, MacLeod和 McCarty(艾菲里一麦克劳德一麦卡蒂 )研究小组确认该未知物质为DNA。 　　At about the same time P.A. Levene discovered that DNA contained four nitrogenous [na?tr?d??n?s] bases, each of which was attached to a sugar molecular and a phosphate group- a combination Levene termed a nucleotide. 　　与此同时， P.A. Levene(列文 原名Phoebus Aaron Theodor)发现DNA含有四种碱基，并且每一个碱基都与一个磷酸分子和一个糖分子连接，称为核苷酸。 * * 　　Disagreement over whether DNA could carry complex genetic information was ended in the early 1950s by Martha Chase and Alfred Hershey, whose work with E. coli showed clearly that DNA, and not protein, is the bearer of genetic information. 　　在20世纪50年代初,Martha Chase and Alfred Hershey(马莎·蔡斯和阿尔弗雷德·赫尔希)通过对大肠杆菌实验表明，遗传信息的携带者是DNA ，而不是蛋白质，从而结束了DNA 是否携带遗传信息的争议 。 * * 　　 Each DNA nucleotide contains a five-carbon sugar, deoxyribose, attached to one of four bases; adenine, guanine, cytosine, or thymine. 　　每个核苷酸都含有一个五碳脱氧核糖，分别连接4个碱基，即：腺嘌呤，鸟嘌呤，胞嘧啶，胸腺嘧啶。 　　Adenine and guanine moleculars are double-ring structures called purines, while cytosine and thymine are single-ring structures called pyrimidines. 　　腺嘌呤和鸟嘌呤是双环结构称为嘌呤；胞嘧啶和胸腺嘧啶是单环结构称为嘧啶．　 * * 　　The molecule made up of a base plus a sugar is termed a nucleoside. In each molecule of D