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Viruses

Viruses. 11.2. Are viruses ‘Living’?. _________ Life-like characteristics: ____________________________ ____________________________ Non Life-like characteristics ____________________________ ____________________________ ____________________________. Viral Reproduction.

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Viruses

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  1. Viruses 11.2

  2. Are viruses ‘Living’? • _________ • Life-like characteristics: ____________________________ ____________________________ • Non Life-like characteristics ____________________________ ____________________________ ____________________________

  3. Viral Reproduction • Recall the four stages of viral reproduction: • Attachment/Entrance • Attaches to specific receptor cites on plasma membrane of the host cell  “keys” or “jigsaw puzzle” • Each virus has a specifically shaped attachment protien  virus can only attach to a few specific types of cells (___________ range). • Example: T4 virus can only infect bacterial cells. It will NOT attach to plant or animal cells. • Example: Polio: can only infect human intestinal and nerve cells. • Two ways of entrance: • Nucleic acid of virus injected into the cell • Cell engulfs the virus (endocytosis) if the virus is surrounded by an envelope (disguised) • Creates a vacuole inside the host cell  nucleic acid breaks out of vacuole. • Synthesis • Virus causes cell to make its own materials: protein coats and nucleic acids • Assembly • Virus uses cell’s machinery to create new viruses • Release • Cell becomes so full of virus that it lyses.

  4. Viral Replication Cycles • Lytic Cycle • Virus infects host and makes more viruses http://www.youtube.com/watch?v=wVkCyU5aeeU • Lysogenic Cycle • Virus coexists with the cell for a period of time • Eventually enters the lytic cycle http://www.youtube.com/watch?v=_J9-xKitsd0&feature=related

  5. The Lytic Cycle • Takes about 30 minutes, producing up to 200 new viruses.

  6. The Lysogenic Cycle DNA enters and is integrated into the host cell’s DNA. Cell replicates with viruses DNA in the cell genome. (can happen many many times) Chemical trigger causes cells to start making virus.

  7. Lysogenic vs. Lytic Cycles

  8. Viruses and Disease • Many diseases are caused by viruses • Destruction of host cells causes symptoms of disease • Vaccines are used to prevent viral infection

  9. Vaccines • Are needed because antibiotics DO NOT kill viruses • Antibiotic:__________________ • Contains non-infections virus particles. • Causes the body to react and make antibodies against the virus. • Body is ready to fight infection by the real virus.

  10. Types of Viruses • DNA Viruses • RNA Viruses • Subgroup of RNA viruses is called  Retroviruses

  11. DNA Viruses • Genome is double stranded • If mutation in one strand of DNA, ‘spell check’  mutations corrected • Therefore, DNA viruses usually don’t mutate (new strains are rare) • Immune system always recognize the virus! MAINTAINS ITS’ IDENTITY!

  12. RNA Viruses • Genome is single-stranded (RNA) • If mutation on the one strand, permanent change • New strains are common • Immune system may not recognize the new mutated virus • New antibodies (part of immune system) need to be made. CAN NOT CARRY OUT LYSOGENIC CYCLE! Why? • Cells usually contain DNA = double stranded • Single-stranded RNA can not ‘hide’ in the double-stranded DNA: does not fit.

  13. Retroviruses • Contain an enzyme (called reverse transcriptase) that allows them to change their genome from RNA to DNA. • Therefore, able to carry out the lysogenic cycle. • More dangerous than DNA and RNA. Why? • Can mutate • Can lay dormant

  14. Seatwork/Homework • Read textbook pages 385-389 • Answer question #1-5, 7-8. • Read and summarize the sections on Viruses and Biotechnology, the Viral Genome, and Origin of Viruses.

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