{"id":4611,"date":"2019-06-24T13:08:33","date_gmt":"2019-06-24T13:08:33","guid":{"rendered":"https:\/\/pressbooks.ccconline.org\/acchumanbio\/chapter\/5-15-genetic-engineering-3\/"},"modified":"2023-11-30T18:24:23","modified_gmt":"2023-11-30T18:24:23","slug":"5-15-genetic-engineering-3","status":"publish","type":"chapter","link":"https:\/\/pressbooks.ccconline.org\/acchumanbio\/chapter\/5-15-genetic-engineering-3\/","title":{"raw":"5.16\u00a0Genetic Engineering","rendered":"5.16\u00a0Genetic Engineering"},"content":{"raw":" \r\n\r\n[h5p id=\"512\"]\r\n\r\nFigure 5.16.1 Potato plants: One genetically engineered and healthy (left), and one infected with bacterial ring rot (right).<\/em>\r\n
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Please Pass the Potatoes<\/h1>\r\n<\/div>\r\nYou might want to pass on the potato plants on the right in Figure 5.16.1. They are infected with a virus, which is quickly killing them. The potato plants on the left are healthy and productive. Why aren't they infected with the same virus? The plants on the left have been genetically engineered to make them resistant to the virus.\r\n
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What Is\u00a0Genetic Engineering?<\/h1>\r\n<\/div>\r\n[pb_glossary id=\"2585\"]Genetic engineering[\/pb_glossary]<\/strong> is the use of technology to change the genetic makeup of living things for human purposes. Generally, the goal of genetic engineering is to modify organisms so they are more useful to humans. Genetic engineering, for example, may be used to create crops that yield more food or resist insect pests or viruses, such as the virus-resistant potatoes pictured (left) in Figure 5.16.1 . Research is also underway to use genetic engineering to cure human genetic disorders with gene therapy.\r\n
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Genetic Engineering\u00a0Methods<\/h1>\r\n<\/div>\r\nGenetic engineering\u00a0uses a variety of techniques to achieve its aims. Two commonly used techniques are gene\u00a0cloning\u00a0and the polymerase chain reaction.\r\n

Gene\u00a0Cloning<\/h2>\r\n[pb_glossary id=\"2586\"]Gene cloning[\/pb_glossary]<\/strong>\u00a0is the process of isolating and making copies of a gene. This is useful for many purposes. For example, gene cloning might be used to isolate and make copies of a normal gene for\u00a0gene therapy. Gene cloning involves four steps: isolation, ligation, transformation, and selection.\r\n
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  1. In the\u00a0isolation<\/strong>\u00a0step, an\u00a0[pb_glossary id=\"5757\"]enzyme[\/pb_glossary]\u00a0is used to break\u00a0[pb_glossary id=\"277\"]DNA[\/pb_glossary]\u00a0at a specific\u00a0base\u00a0sequence. This is done to isolate a [pb_glossary id=\"5521\"]gene[\/pb_glossary].<\/li>\r\n \t
  2. During\u00a0ligation<\/strong>, the enzyme DNA ligase combines the isolated gene with plasmid DNA from bacteria. (Plasmid DNA is circular DNA that is not part of a chromosome and can replicate independently). The DNA that results is called recombinant DNA<\/strong>.<\/li>\r\n \t
  3. In\u00a0transformation<\/strong>, the\u00a0recombinant DNA\u00a0is inserted into a living cell, usually a bacterial cell.<\/li>\r\n \t
  4. Selection<\/strong>\u00a0involves growing transformed\u00a0bacteria\u00a0to make sure they have the\u00a0recombinant DNA. This is a necessary step because transformation is not always successful. Only bacteria that contain the recombinant DNA are selected for further use.<\/li>\r\n<\/ol>\r\n
    \r\n\r\n[h5p id=\"513\"]\r\n\r\nPolymerase Chain Reaction<\/span>\r\n\r\n<\/div>\r\nThe\u00a0polymerase chain reaction (PCR)<\/strong> makes many copies of a gene or other DNA segment. This might be done in order to make large quantities of a gene for genetic testing. PCR involves three steps: denaturing, annealing, and extension. The three steps are illustrated in Figure 5.16.2. They are repeated many times in a cycle to make large quantities of the gene.\r\n
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    1. Denaturing<\/strong>\u00a0involves heating DNA to break the bonds holding together the two DNA strands, yielding two single strands of DNA.<\/li>\r\n \t
    2. Annealing<\/strong>\u00a0involves cooling the single strands of DNA and mixing them with short DNA segments called primers. Primers have\u00a0base\u00a0sequences that are complementary to segments of the single DNA strands. As a result, bonds form between the DNA strands and primers.<\/li>\r\n \t
    3. Extension<\/strong> [or Elongation] occurs when an enzyme (Taq polymerase or Taq DNA polymerase) adds nucleotides to the primers. This produces new DNA molecules, each incorporating one of the original DNA strands.<\/li>\r\n<\/ol>\r\n[caption id=\"attachment_2587\" align=\"aligncenter\" width=\"1000\"]\"Polymerase Figure 5.16.2 The polymerase chain reaction involves three steps, and high temperatures are needed for the process to work. The enzyme Taq polymerase is used in step three because it can withstand high temperatures.<\/em>[\/caption]\r\n\r\n
      \r\n\r\n \r\n\r\n<\/div>\r\nUses of Genetic Engineering<\/span>\r\n\r\nMethods of\u00a0genetic engineering\u00a0can be used for many practical purposes. They are used widely in both medicine and\u00a0agriculture.\r\n

      Applications in Medicine<\/h2>\r\n[caption id=\"attachment_2589\" align=\"alignright\" width=\"356\"]\"Genetic Figure 5.16.3 Genetically Engineering Bacteria to Produce a Human Protein. Bacteria can be genetically engineered to produce a human protein, such as a cytokine. A cytokine is a small protein that helps fight infections.<\/em>[\/caption]\r\n\r\nIn addition to [pb_glossary id=\"2573\"]gene therapy[\/pb_glossary] for [pb_glossary id=\"2562\"]genetic disorders[\/pb_glossary], [pb_glossary id=\"2585\"]genetic engineering[\/pb_glossary] can be used to transform [pb_glossary id=\"2588\"]bacteria[\/pb_glossary] so they are able to make human [pb_glossary id=\"1593\"]proteins[\/pb_glossary] (see Figure 5.16.3). Proteins made by the bacteria are injected into people who cannot produce them because of mutations.\r\n\r\n[pb_glossary id=\"2590\"]Insulin[\/pb_glossary] was the first human\u00a0protein\u00a0to be produced in this way. Insulin helps\u00a0cells\u00a0take up glucose from the\u00a0blood. People with type 1\u00a0diabetes have a\u00a0mutation\u00a0in the gene that normally codes for insulin. Without insulin, their blood glucose rises to harmfully high levels. At present, the only treatment for type 1 diabetes is the injection of insulin from outside sources. Until recently, there was no known way to make human insulin outside the\u00a0human body. The problem was solved by gene cloning. The human insulin gene was cloned and used to transform bacterial cells, which could then produce large quantities of human insulin.\r\n

      Applications in\u00a0Agriculture<\/h2>\r\nGenetic engineering\u00a0has been used to create transgenic crops.\u00a0[pb_glossary id=\"2591\"]Transgenic crops[\/pb_glossary]<\/strong> are genetically modified with new genes that code for traits useful to humans.\r\n\r\nTransgenic crops have been created with a variety of different traits. They can yield more food, taste better, survive drought, tolerate salty soil, and resist insect pests, among other things. Scientists have even created a transgenic purple tomato (Figure 5.16.4) that contains high levels of cancer-fighting compounds called antioxidants.\r\n\r\n[caption id=\"attachment_2592\" align=\"aligncenter\" width=\"302\"]\"Purple Figure 5.16.4 A purple tomato is genetically modified to contain high levels of antioxidants. A gene for the compound was transferred into normal red tomatoes.<\/em>[\/caption]\r\n\r\n
      \r\n\r\nEthical, Legal, and Social Issues<\/span>\r\n\r\n<\/div>\r\nThe use of\u00a0genetic engineering\u00a0has raised a number of ethical, legal, and social issues. Here are just a few:\r\n