Chapter 18 - The Genetics of Viruses and Bacteria

Chapter 18 - The Genetics of Viruses and Bacteria - Chapter...

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Chapter 18 Class Notes – The Genetics of Viruses and Bacteria – Page 1 Max Sauberman AP Biology – Mr. Schilp Chapter 18 The Genetics of Viruses and Bacteria Microbial Model Systems: Viruses called bacteriophages can infect and set in motion a genetic takeover of bacteria such as E. coli. Viruses are not alive, and cannot reproduce without a host. E. coli and its viruses are called model systems because of their frequent use by researchers in studies that reveal broad biological principles. Beyond their value as model systems, viruses and bacteria have unique genetic mechanisms that are interesting in their own right. Bacteria vs. Viruses: Bacteria are prokaryotes with cells much smaller and more simply organized than those of eukaryotes. Viruses are smaller and simpler than bacteria. Virus Reproduction: Viruses have genomes, but can reproduce only within a host cell. This is why they’re not quite considered alive. Scientists detected viruses indirectly long before they could see them. The story of how viruses were discovered begins in the late 1800s. The Discovery of Viruses: Tobacco mosaic disease stunts the growth of tobacco plants and gives their leaves mosaic coloration. In the late 1800s, researchers hypothesized that a particle smaller than bacteria caused the disease. In 1935, Wendell Stanley confirmed this hypothesis by crystallizing the infectious particle, now known today as tobacco mosaic virus. Viral Structure: Viruses are not cells, but small infectious particles consisting of nucleic acid enclosed in a protein coat and, in some cases, a membranous envelope. Viral genomes may consist of double- or single-stranded DNA or RNA, which is significant for viral diversity. Depending on the type of nucleic acid, a virus is called a DNA virus or an RNA virus.
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Chapter 18 Class Notes – The Genetics of Viruses and Bacteria – Page 2 Capsids and Envelopes: A capsid is the protein shell that encloses the viral genome, and can have various structures. Glycoproteins on the capsid are used for cell-cell recognition. The immune system uses them to determine a virus, and can use the cell membrane to shield them. Some viruses have structures with membranous envelopes that help them infect hosts, and make them less easy to detect. These viral envelopes surround the capsids of influenza virus and many other animal viruses. Viral envelopes, derived from the host cell membrane, contain a combination of viral and host cell molecules. Phages: Bacteriophages, also called phages, are viruses that infect bacteria. They have the most complex capsids found among viruses. Phages have an elongated capsid head that encloses their DNA. A protein tailpiece attaches the phage to the host and injects the phage DNA inside General Features of Viral Reproductive Cycles: Viruses are obligate intracellular parasites (they harm their hosts), meaning they can only reproduce within a host cell. Each virus has a host range, a limited number of host cells that it can infect.
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This note was uploaded on 03/17/2011 for the course BIO 101 taught by Professor Sullivan during the Spring '08 term at Harvard.

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Chapter 18 - The Genetics of Viruses and Bacteria - Chapter...

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