Lecture 8- prokaryotic molecular genetics

Lecture 8- prokaryotic molecular genetics - As you have...

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As you have seen, our understanding of the role of DNA in heredity has benefited greatly from the fact that viruses and bacteria use the same genetic material and the same genetic code that we do. It's much easier to manipulate bacteria and viruses than higher organisms. How long might it have taken to understand the nature of the genetic material were it not for Frederick Griffith's transformation assay in S. pneunoniae or Hershey and Chase with their bacteriophage and their Waring blender. But those are not the sum total of what viruses and bacteria have to teach us and, moreover, the ability to harness these organisms has been the key our current ability to manipulate DNA. Bacteria and viruses are the hammer and tongs of genetic engineering. So let's look in more detail at how they work. Real viruses, like computer viruses, are basically just a set of instructions for subverting the host (cell or computer) and making it do something not necessarily in the host's best interest. In the case of viruses the set of instructions, encoded by the viral DNA, tell the cell to stop doing cell stuff and start making more virus. It's amazing how few instructions it takes to do this. Some viruses, like influenza and certain phage, have less than 10 genes. Consequently they can be, and generally are, very small and difficult to detect. The first assay (and still often the best assay) for viruses was based on their ability to cause disease. However, it was not until the size of disease-causing agents could be measured that it was possible to distinguish diseases caused by viruses from those caused by bacteria. Dmitri Ivanovsky was the first to do this. He showed that the disease called tobacco mosaic disease was caused by an agent that could pass through a filter that a bacterium won't fit through. So viruses were initially defined as "a disease agent that’s smaller than a bacterium"; the first being the aptly named tobacco mosaic virus. This was the start of a huge effort to identify and classify viruses that continues today. Since all virions (virus particles) consist of a simple protein coat or capsid and nucleic acid, there wasn't much to differentiate viruses based on their structure.
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The classification took into account things like: host specificity (plants, animals, bacteria), whether and how it uses RNA or DNA as its genetic material and the shape and size of the virus. One of the main divisions distinguishes viruses that infect bacteria (bacteriophage) and
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Lecture 8- prokaryotic molecular genetics - As you have...

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