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VIRUSES

Learn about viruses, their structure, and how they reproduce. Discover why viruses are considered non-living and why antibiotics cannot cure viral infections.

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VIRUSES

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  1. VIRUSES

  2. What is a Virus? • A virus is a piece of genetic material (DNA or RNA) surrounded by a protective protein coat, called a capsid. • The capsid helps to protect the virus from being destroyed by the hosts immune system Capsid

  3.  Viruses come in a variety of shapes • They are NOT considered to be a living thing.

  4. Why are viruses considered non-living? • No cell structures, like cytoplasm, organelles or cell membranes • No cellular respiration • They cannot reproduce on their own

  5. How does a virus reproduce? Viruses have a LyticCycle. This means it destroys its host’s cell when they reproduce. • ATTACHMENT – The virus attaches itself to a host cell, to a specific receptor site on the cell membrane. • ENTRY –The virus enters the cell. This can happen in 2 ways: • Only the DNA/RNA is injected into the host cell (ex: T4 virus) • The whole virus enters, through Receptor-mediated endocytosis

  6. 3. REPLICATION –The host cell’s metabolism replicates (copies) the viral DNA/ RNA 4. ASSEMBLY - New virus particles are assembled inside the host cell 5. LYSIS AND RELEASE -The host cell breaks (lyses) open releasing the new virus particles http://www.courses.fas.harvard.edu/~biotext/animations/lyticcycle.html

  7. Lytic Cycle Diagram DRAW DIAGRAM IN NOTES: Page 123, figure 4.21 in textbook

  8. T4 Virus infecting a bacteria • http://www.youtube.com/watch?v=41aqxcxsX2w&feature=BFa&list=PL998C063DCABF2E7E&safety_mode=true&persist_safety_mode=1&safe=active Flu Attack! How A Virus Invades Your Body http://www.youtube.com/watch?v=Rpj0emEGShQ&feature=related&safety_mode=true&persist_safety_mode=1&safe=active

  9. Questions • DRAW CYCLE IN NOTES: Page 123, figure 4.21 2. Why must a virus enter a host cell in order to reproduce itself? 3. A doctor tells a patient that an antibiotic will not help cure a cold sore. Explain the doctors reasoning.

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