mcdb20lec12su09 - Lecture 12 Noncellular Infectious Agents:...

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Lecture 12 Noncellular Infectious Agents: Viruses, Viroids, Prions Population Ecology 2 Penicillin Many derivatives Blocks cell wall synthesis Growing bacteria lyse (Slow-growing bacteria take longer to die) Weakening cell wall 3 4 What are Viruses? Non living infectious particle Every virus has a genome and a coat Some also have a membrane envelope Different viruses infect all forms of living cells Estimate of 10 32 viruses on earth 5 • Some cause disease, some do not • Vary in size and shape – Rod-shaped, spherical, coil, helix • Vary in type of genome Viral genome contains sufficient information to take over host cell and make more viruses 6 Viral Life Cycle All viruses must: 1. Attach to specific host cell 2. Get viral genome into host cell 3. Replicate genome 4. Make viral proteins 5. Assemble capsids 6. Release progeny viruses from host cell All viruses infect cells by binding to specific receptors via surface glycoproteins Viruses that infect bacteria are called bacteriophages Why do flu viruses change quickly? DNA vs. RNA viruses ! DNA viruses are relatively stable because DNA replication enzymes check for errors and correct them during replication. ! RNA viruses change quickly because RNA replication enzymes do not have error- checking mechanisms. :: RNA viruses mutate into new forms rapidly and regularly.
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lasted from March 1918 - June 1920 500,000,000 humans infected 50-100M humans died 1918 Flu Pandemic (“Spanish Flu”) ! Influenza virus has segmented genome composed of 7 RNA molecules. ! several distinct types of viral antigens Hemagglutinin and Neuraminidase (e.g. H1N1, H1N5, . ... ) ! Many flu viruses can infect more than one species Bird Flu ! Bird flu is exceptionally lethal, but is poorly taken up by human cells ! So far, human bird flu requires close contact with infected flocks of birds or by eating birds that had died of the virus. ! WHO and national health agencies are preparing for a worldwide pandemic. ! The avian influenza virus that is currently spreading around the world does not readily infect humans, but that situation could change. ! If genetic material from an avian influenza virus mixed with material from a human flu, the result could be a new form of the lethal virus that does infect humans. Swine Flu ! Swine flu is less lethal than “seasonal flu” in humans ! Swine flu virus particles released in lungs before symptoms appear ! Quickly spread within human populations What if? ! Pig cell + bird virus + human virus ! might produce a new form of the virus that carries the gene segments from both human and bird viruses ! could make new virus with gene that
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This note was uploaded on 09/14/2009 for the course MCDB 20 taught by Professor Cooper during the Summer '08 term at UCSB.

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mcdb20lec12su09 - Lecture 12 Noncellular Infectious Agents:...

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