[专业英语考试复习资料]专业八级分类模拟198.docx
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1、专业英语考试复习资料专业八级分类模拟198专业英语考试复习资料专业八级分类模拟198专业八级分类模拟198LISTENING COMPREHENSIONSECTION A MINI-LECTUREIn this section you will hear a mini-lecture. You will hear the mini-lecture ONCE ONLY. While listening to the mini-lecture, please complete the gap-filling task with NO MORE THAN THREE WORDS for each g
2、ap. Make sure the word(s) you fill in is (are) both grammatically and semantically acceptable. You may use the blank sheet for note-taking. You have THIR TY seconds to preview the gap-filling task. Now listen to the mini-lecture. When it is over, you will be given THREE minutes to check your work. T
3、he Cloning Technology . The difference between a 1 colony and cloning a mammal A. Clarify the illusion: scientists have been cloning genes for years. B. Definition of clone: a clone is population of cells produced by 2 ; all the cells in a clone have exactly the 3 , using a process known as recombin
4、ant 4 technology. C. Clone a mammal: nuclear transfer. . Genes, chromosomes and the genome A. Genes - DNAits 5 makes it divide easily. - 6 of chemical groups within DNA form genes. - Genes determine what 7 a given cell will have. B. Chromosomes: genes are linked together to form chromosomes. C. Geno
5、me: the entire collection of chromosomes in each cell. D. 8 genes enables scientists to mass-produce proteins that can be used to 9 . . The process of cloning a gene A. Remove DNA from the cell. B. DNA is cut into pieces using 10 . C. To replicate DNA, attach them to non-mammalian DNA. D. Plasmids a
6、re easily incorporated into 11 and multiply by themselves. E. The plasmid carries the gene into a 12 cell. F. The gene 13 a plasmid and some proteins. G. The plasmid 14 . H. Copies passed to the cells 15 . I. Each cell contains one or more copies of the recombinant DNA molecule. The gene is now cons
7、idered cloned. (如需获取本MP3听力录音请搜索标题名) 1.答案:single cell听力原文 The Cloning Technology Today, we are going to talk about the cloning technique. First, we will see the difference between a single cell colony and cloning a mammal. Then we will focus on cell cloning process and its scientific use. In March 19
8、97, the world said hello to Dolly, the first mammal to be cloned from an adult cell. We asked ourselves: Would the world soon be populated with human clones? Did you know that cloning isnt new? In fact, scientists have been cloning genes for many years in laboratories around the world. Of course, cl
9、oning a genes and cloning a whole mammal are quite different in terms of process and product. But just how do you get from a single cell to a clone? We generally think of cloning as producing a duplicate of something. Scientists, however, usually use the term clone in referring to cells. A clone is
10、population of cells produced by one ancestor. Because of the way cells multiply, all the cells in a clone have exactly the same genetic makeup. Gene cloning uses a process known as recombinant DNA technology. By contrast, cloning a mammal, such as the sheep Dolly, involves a technology known as nucl
11、ear transfer. Although the end result is the same, the actual processes of gene cloning and mammalian cloning are quite different. But we need to start from the beginning to understand how these complicated and amazing bioengineering technologies evolved. Now, we will study on what genes, chromosome
12、s, and the genome are. Within the body of a mammal, tissues are made of cells. Inside each cell is a long molecule called DNA. Its shape enables it to divide easily. Arrangements of chemical groups within DNA form genes. Genes direct cells to produce proteins, and thus determine what function a give
13、n cell will have. For example, skin cells produce proteins which are present in skin tissue, and blood cells produce a protein present in blood. Genes essentially tell each cell what type it is. Genes are linked together to form chromosomes. The entire collection of chromosomes in each of your cells
14、 is called genome. All the cells in your body contain the same genome. Once you realize that all cells contain the information for making the whole organism, you know that cloning is theoretically possible. But what makes a skin cell different from a blood cell? The chromosomes within the nucleus of
15、 each cell are folded in various ways. Genes that are buried within the chromosomes are inactive, or switched off, while genes on the surface of the chromosomes are active. In a skin cell, the genes for producing skin proteins are active, while in a blood cell, the gene is active. Gene cloning is th
16、e process of producing a population of cells all of which contain a specific gene. Using these identical cells, scientists can study the entire genome and obtain clues to how genes are switched on and off. Cloning genes also enables scientists to mass-produce proteins that can be used to treat a var
17、iety of diseases. For example, the cells in the pancreas produce a protein called insulin which is important in helping the body maintain appropriate blood sugar levels. Some people have a disease called diabetes because their cells dont produce enough insulin. Cloning the insulin gene has provided
18、a way of producing large amounts of human insulin which is used to treat diabetes. Then, we are going to disclose the mystery of cloning a gene. To clone a gene, scientists remove the DNA from a cell, isolate the specific gene of interest, and then get it to multiply. Sound simple? Not so fast. Lets
19、 look at each step. First the DNA must be removed from the cell. Over the years scientists have perfected chemical methods for doing this, based on the physical properties of DNA molecules. The DNA is then cut into pieces using special proteins. You may think of these special proteins as little kniv
20、es programmed to cut the DNA in specific places. By using the correct special proteins, scientists can isolate whatever gene they want. Once the gene is isolated, it can then be duplicated. Mammalian genes do not reproduce by themselves, however. To replicate them, scientists attach them to pieces o
21、f non-mammalian DNA that do replicate on their own. The most common procedure uses small circular pieces of DNA called plasmids that come from bacteria. Plasmids have two useful characteristics. They are easily incorporated into bacteria, they multiply by themselves inside bacteria. The gene of inte
22、rest is combined with a plasmid and some proteins. The proteins open the plasmid circle and stitch in the new gene. The result is a recombinant DNA molecule. The plasmid carries the gene into a host cell. Once inside the host, the plasmid multiplies, making lots of copies of itself and the gene it c
23、ontains. When the host cell divides, copies of the recombinant DNA molecule are passed to the cells offspring. As the bacterial cells continue to divide, a colony of identical cells is produced. Each cell contains one or more copies of the recombinant DNA molecule. The gene is now considered cloned.
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