发布时间 : 星期四 文章生物专业英语中英文对照（蒋悟生）第2版 Bioengineering English更新完毕开始阅读
Bioengineering English
Lesson Five
Discovering the Chemical Nature of the Gene
Genes Code for Particular Proteins
The first scientist to investigate the question of how genes affect phenotype was Sir Archibald Garrod, whose studies of alkaptonuria implied a relationship between genes and enzymes. Thirty years later Beadle and Ephrussi showed a relationship between particular genes and biosynthetic reactions responsible for eye color in fruit flies. Next, in a series of classic experiments on the effects of mutations in the bread mold Neurospora crassa, Beadle and Tatum explored the one-gene-one-enzyme hypothesis-the idea that each gene codes for a particular enzyme. Their work paved the way for other researchers to elucidate the precise ways in which enzymes affect complex metabolic pathways.In 1949, in research on the role of hemoglobin in sickle cell anemia, Linus
Pauling
helped
refine
the
one-gene-one-enzyme
hypothesis
into
the
one-gene-one-polypeptide hypothesis.
Archibald Garrod是第一个研究基因是如何影响表型的科学家，他对尿黑酸症的研究揭示了基因与酶之间的关系。Beadle 和Ephrussi在三十年后对果蝇眼睛颜色的研究发现特殊基因与相关反应的生物合成有关。接着对面包发霉粗糙脉孢菌的突变试验得出一个基因一个酶的假说。他们的工作为其他工作者铺平了道路，即精确地阐明了酶影响了复杂的新陈代谢途径。在1949年，对镰刀状细胞贫血症的研究对一个基因一个酶的假说进一步上升为一个基因一个多肽。
The Search for the Chemistry and Molecular Structure of nucleic Acids
Nuclei acid, originally isolated by Johann Miescher in 1871, was identified as a prime constituent of chromosomes through the use of the red-staining method developed by Feulgen in the early 1900s. Frederick Griffith's experiments with the R and S stains of pneumococci showed
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that an as yet unknown material from one set of bacterial could alter the physical traits of a second set. In the 1940s the team of Avery, MacLeod, and McCarty showed that this unknown material was DNA. At about the same time P.A. Levene discovered that DNA contained four nitrogenous bases, each of which was attached to a sugar molecule and a phosphate group-a combination Levene termed a nucleotide.
在1871年，核酸最初是由Johann Miescher分离成功，并由Feulgen在1900年证实核酸是染色体组最基本的组成。Frederick Griffith对粗糙和光滑的肺炎球菌实验表明，不确定的某种物质可以从一组细菌转移到另一种细菌中。在1940年，确认该物质为DNA。四个碱基和磷酸分子分别连接在糖分子上，称核苷酸。
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.
直到1950年，通过对大肠杆菌实验发现，遗传物质是DNA，而不是蛋白质。
Each DNA nucleotide contains a five-carbon sugar, deoxyribose, attached to one of four bases: adenine, guanine, cytosine, or thymine. Adenine and guanine molecules are double-ring structures called purines, while cytosine and thymine are single-ring structures called pyrimidines. The molecule made up of a base plus a sugar is termed a nucleoside. In each molecule of DNA a phosphate group links the five-carbon sugar of one nucleoside to the five-carbon sugar of the next nucleoside in the chain. This phosphate bonding creates a sugar-phosphate backbone.
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。碱基连接糖称核苷。磷酸键形成磷酸骨架。
Chargaff’s rules describe the fact that (1) the amount of adenine is equal to the amount of thymine in DNA, with amount of cytosine equal to that of guanine, and (2) the ratios of A to T and of C to G vary with different species.
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（1）腺嘌呤与胸腺嘧啶，胞嘧啶与鸟嘌呤相等；（2）腺嘌呤与胸腺嘧啶，胞嘧啶与鸟嘌呤的比例随物种不同而不同。
The Research Race for the Molecular Structure of DNA
In the late 1940s and early 1950s, researchers looking for the structure of DNA drew upon Chargaff s insight, Levene's ideas on DNA components, and two other lines of evidence. One was the suggestion of Linus Pauling that DNA might have a helical structure held in place by hydrogen bonds, and the other was X-ray diffraction photos of DNA, showing a helical structure with distance between the coils, taken by Franklin and Wilkins.
直到40年代末50年代初，研究者在寻求DNA结构过程中，确立了Chargaff 的观点和, Levene的组成理论以及其他两个线索。一个是Linus Pauling的假设，DNA可能具有螺旋结构，通过氢键连接。另一个是X-衍射图片，Franklin and Wilkins提供。
Based on this information Watson and Crick proposed the double helix model of DNA-A twisted ladder-like molecule with two outer sugar phosphate chains and rungs formed by nucleotide pairs. Paired nucleotides, which always occur as A-T or G-C, are linked by hydrogen bonds. Watson and Crick also proposed that genetic information is encoded by the sequence of base pairs along the DNA molecule.
基于这些信息，Watson 和 Crick提出了双螺旋结构模型，成对的核苷酸通过氢键相连，遗传信息就贮藏在碱基对中。 How DNA Replicates
In their model of DNA structure and function, Watson and Crick hypothesized that DNA replicates itself by \. This process would produce two opposite halves that could then serve as templates for the construction of new, complementary strands. This model of semiconservative replication conservative because each new molecule has one half of the former parent molecule-was later confirmed by the work of DNA进行复制是以拉链方式自我复制，产生的两个二分体分别为模板生成互补链，即半
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保留复制。并由Meselson 和 Stahl验证。
In E. coli DNA replication begins with the formation of a bubblelike structure on the circular chromosome that is produced by replication forks. Studies of bacterial DNA replication have shown that a growing DNA chain lengthens only in the 5' to 3' direction (from the 5' carbon of one sugar to the 3' carbon of the next). The leading strand is synthesized continuously, while the lagging strand is synthesized in short stretches known as Okazaki fragments. The enzyme DNA polymerase links free nucleotides as they line up on the template formed by the original strand of the parent molecule.
In eukaryotes DNA replication follows the same general principles as in prokarotes. On the long DNA molecules replication proceeds (in two directions at once) from hundreds or thousands of points of origin.
大肠杆菌复制开始时形成泡样复制叉，链生长方向由5′向3′端，前导链连续生成，后随链由冈崎片段组成，由DNA聚合酶催化。真核生物复制与原核生物复制相似，但有几百到几千个复制原点（原核一般只有一个复制原点）。
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