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Viruses
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Homework Cell Analogy Project due Monday 10/5
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Objectives Know the two major differences between a virus and a cell Know how a virus replicates itself
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Viruses How many viruses can the class name off the tops of our heads?
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Viruses How many viruses can the class name off the tops of our heads? HIV, influenza, H1N1, rhinovirus, herpes, HPV, smallpox, polio, chickenpox, ebola, hanta, avian influenza, SARS, hepatitis, norovirus, dengue, Epstein-Barr, marburg, filoviruses Major viruses you probably haven’t heard of include viruses infecting other animals (SIV, foot and mouth), many plant viruses (tobacco mosaic virus), bacteria viruses like T4 phage
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Viruses Is a virus another kind of bacteria? How do they cause damage to the infected organism?
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Definition Virus = a microscopic infectious agent that replicates but is not truly alive* *By most scientists’ reckoning
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Viruses Viruses are not cells. They have only two real parts, and only one of them can also be found in cells.
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Viruses They consist of a protein capsid (envelope or shell) that contains genetic material. Often this genetic material is DNA, like a cell. Sometimes it’s closely- related RNA instead, in what are called retroviruses.
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Viruses This means cells have what parts that viruses don’t? What does this mean that viruses cannot do for themselves?
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Viruses A virus can do one thing and one thing only: they force a cell (a host) to make more copies of the virus.
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Viral Replication http://videos.howstuffworks.com/hsw/80 61-viruses-how-viruses-work-video.htm http://videos.howstuffworks.com/hsw/80 61-viruses-how-viruses-work-video.htm http://www.hhmi.org/biointeractive/medi a/viral_lifecycle-lg.mov http://www.hhmi.org/biointeractive/medi a/viral_lifecycle-lg.mov http://student.ccbcmd.edu/courses/bio141 /lecguide/unit3/viruses/adlyt.html http://student.ccbcmd.edu/courses/bio141 /lecguide/unit3/viruses/adlyt.html In spite of this, it’s not usually lysing cells that cause pain and symptoms, but it’s actually the body’s defense mechanisms that cause discomfort.
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Checkpoint How is a virus different from a cell? How is viral replication different from how a cell can reproduce?
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Viruses in History Smallpox and the destruction of Native American civilizations Mexico’s population: 18 million to 1.6 million in 100 years American & Canadian Nations reduced to 5% of former population (20 million) in 200 years Smallpox eradication in 20th century
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Viruses in History Influenza Pandemic of 1918 http://videos.howstuffworks. com/hsw/8063-viruses-the- influenza-pandemic-of- 1918-video.htm http://videos.howstuffworks. com/hsw/8063-viruses-the- influenza-pandemic-of- 1918-video.htm
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Viruses in History HIV pandemic HIV mutated from SIV The more closely related two species are, the easier it is for them to share viral illnesses Discovered in the 1980s, 25 million dead since 1981 1/3 in Subsaharan Africa, ~6% children Fast mutating, no cure or vaccine yet. Clearly understood transmission & pathology Many treatments & application of evolutionary principles mean it’s no longer “a death sentence” with medical assistance, but still a pandemic.
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Viruses in History Applications in Biotechnology Knowing what you do about how a virus replicates, why do you think scientists look to viruses to help treat genetic disorders?
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Unanswered Questions Last remaining stores of smallpox in U.S. and Russia? Herd immunity vs. individual freedoms - parents refuse vaccination for children? Viruses used to modify genes for agriculture, medicine?
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