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Viruses

Viruses. AP Biology Unit 2. Images taken without permission from http://www.zo.utexas.edu/faculty/sjasper/images/ebola_virus.jpg and http://www.bioitworld.hu/adat/200316/21662/sars_virus.jpg. “Famous” Viruses. Influenza (the Flu virus) Actually many different strains (including H1N1)

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Viruses

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  1. Viruses AP Biology Unit 2 Images taken without permission from http://www.zo.utexas.edu/faculty/sjasper/images/ebola_virus.jpg and http://www.bioitworld.hu/adat/200316/21662/sars_virus.jpg

  2. “Famous” Viruses • Influenza (the Flu virus) • Actually many different strains (including H1N1) • Cold Virus (Rhinovirus) • Actually many different strains • HIV • SARS (Coronavirus) • Chicken Pox (Varicella Zoster)

  3. Viruses are nonliving • Viruses are considered nonliving because • They do not have cellular structure • They require another living cell to replicate (copy) themselves –infectious particles • Viruses are very small in size compared to even a bacterium

  4. Capsid Nucleic Acid Viral Envelope Basic Components of a Virus • 3 basic components: • Nucleic Acid (DNA or RNA) • Capsid (Protein Coat surrounding nucleic acid) • Viral Envelope (derived from host cell membranes) – NOT PRESENT IN ALL VIRUSES

  5. Question… • Why might having a viral envelope help a virus? (hint: what does it resemble/ what was it derived from?) • Helps it bind to the host cell • May also help protect it (camouflage it)

  6. Host Range • Viral infection is limited to specific hosts and specific cells within that host • For example: • Rabies – only infects warm-blooded animals • Measles only infects humans • Flu viruses infect the tissues in the upper respiratory tract • HIV only infects specific immune system cells

  7. Viral Reproductive Cycle • Attachment: Virus binds to host cell • Entry: Virus enters host cell • Biosynthesis: Viral genome and proteins are synthesizes • Assembly: New viruses self-assemble • Release: New viruses exit cell (may kill cell in the process)

  8. A Closer Look at Biosynthesis Image obtained without permission from http://bcs.whfreeman.com/thelifewire/default.asp?s=&n=&i=&v=&o=&ns=0&uid=0&rau=0

  9. Nucleic Acid Capsid Bacteriophages • Viruses that infect bacteria • Inject their DNA into host cell • Also called phages

  10. Lytic Cycle • Results in the death of the infected bacteria • Phage that only carry out the lytic cycle are known as virulent phage

  11. Phage DNA is injected in Steps of the Lytic Cycle

  12. Question… • Do you remember how bacteria protect themselves from bacteriophages (foreign DNA)? • They have restriction enzymes to cut them up!

  13. Temperate Phage • Temperate Phage are bacteriophage that can go through the lytic cycle OR the lysogenic cycle • In the lysogenic cycle, the phage does not cause the bacterial host to burst & die

  14. Lysogenic Cycle The lysogenic cycle only consists of this half of the diagram The phage is “dormant” – gets copied with the rest of the DNA

  15. Temperate Phage: Lytic or Lysogenic?

  16. Animal (Human) Viral Infection • Many animal (human) viruses have a viral envelope • There are glycoproteins attached to the viral envelope that help the virus bind to the host cell

  17. Step 2: Through endocytosis Step 1: Glycoproteins on viral envelope bind to receptors on host cell Step 3: Biosynthesis of viral components Step 4: Assembly of Viruses Step 5: New viruses bud out of host cell, gaining a viral envelope

  18. Important Concept • Even though the drawing only shows one new virus coming out, in actuality many (tens of thousands) viruses will come out!

  19. RNA Viruses • Some viruses have RNA as their nucleic acid • Also known as retroviruses • Also have to have reverse transcriptase included in virus • Creates a DNA template from the RNA • Ex. HIV

  20. What about H1N1? • H1N1 is a new strain of the influenza virus • First detected in April 2009 • Why was it called “swine flu”? • originally found that some of the genes in virus were similar to genes in the flu virus in pigs (swine)  later found to be very different • Contains genes from flu viruses found in pigs in Asia, Europe, birds and humans • “quadruple assortment”

  21. What about H1N1? • Why are we so worried about this flu? • Because it’s a new strain that hasn’t been seen before • Most people’s immune systems don’t have immunity against this virus • This will cause more infections than the seasonal flu. • Spreading quickly among young people.

  22. Animations of Lytic & Lysogenic Cycles • Animation

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