Importance of Viruses
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Importance of Viruses

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Importance of Viruses

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1. Importance of Viruses Cause many diseases in plants, animals & humans Some viruses are easily controlled with a vaccine Mumps, Measles, Smallpox, Polio Some viruses are difficult to control with a vaccine Retroviruses (HIV: ssRNA ? dsDNA) Common cold, Influenza (Flu), HIV Used as vectors in biotechnology Used to insert therapeutic genes into a host cell chromosome Use viruses with provirus in life cycle

2. Herpes (dsDNA ? dsDNA)

3. Adenovirus (dsDNA)

4. Polio Virus (ssRNA serves as mRNA)

5. Measles (ssRNA template for mRNA synthesis)

6. Couple at AIDS quilt (HIV: ssRNA ? dsDNA)

7. 1918 Influenza epidemic (ssRNA template for mRNA synthesis)

8. Influenza Today WHO Global Influenza Surveillance Network WHO Global Influenza Surveillance Network

15. Why do new strains of influenza and bird flu arise in Asia?

19. Genetic Changes in Influenza Viruses Antigenic drift ? due to errors in replication and lack of repair mechanism to correct errors Results in ___________________ changes Antigenic shift - reassortment of genetic materials when concurrent infection of different viral strains occurs Results in ___________________ changes

22. Vaccines: Protection against viruses What is a vaccine? Vaccines stimulate the production of memory cells Give long-term protection against a specific antigen Why are vaccines ineffective against the flu virus? Why will this year?s flu vaccine be ineffective next year? Why are vaccines effective against DNA viruses? e.g. small pox and polio virus

23. Smallpox (dsDNA ? dsDNA)

24. Hepatitis B?an RNA virus

25. Viruses and Cancer Tumor Viruses: may transform normal cells into cancer cells Hepatitis B ? Liver cancer HTLV 1 ? leukemia (Human T-Cell Leukemia Virus) Tumor viruses form a permanent provirus Viral oncogenes code for growth factors Growth factors Stimulate cell to enter S phase G1 or G0 ? S phase Each of the following must happen for cancer to occur Active host oncogenes + Active viral oncogenes ? cancer Activators of host oncogenes Carcinogens, radiation, some viruses

26. Emerging viruses

27. Deer Mouse: Carries Hanta virus in Feces

28. Mottling of Squash and Tobacco by the Mosaic Virus

29. Tobacco mosaic virus (RNA virus)

30. Comparing the size of a virus, a bacterium, and a eukaryotic cell

31. Viral structure

32. Viral Structure Nucleic Acid + Protein Coat (Capsid) Some viruses with Membrane (envelope) surrounding capsid Envelope derived from plasma membrane of host cell Helps virus infect host cell No organelles Obligate intracellular parasite Lacks metabolic enzymes, ribosomes, mitochondria Alone, can only infect host cell Nucleic Acid: DNA or RNA Single or Double Stranded 4 genes to a few hundred

34. Host Range Host cell Recognition Complementary fit between external viral proteins and host cell surface proteins Some have a Broad host range Swine flu and rabies viruses Some have a narrow host range Single tissue in a single species e.g. Adenovirus, HIV Phages of E. coli

35. Viral Reproduction Simplified DNA Virus Life Cycle E.g. smallpox, herpes, chickenpox ?Lock and Key? fit between viral surface proteins and host cell receptors initiates endocytosis

36. Electron micrograph of Bacteriophage T4

37. Bacteriophage Reproduction Bacteriophages (Bacterial Viruses) Best understood of all viruses Responsible for many advances in molecular biology Hershey-Chase expmts that showed that DNA is the genetic material Restriction Enzymes used in Genetic Engineering come from bacteria Lytic Cycle of Bacteriophage T4 T4 is a Virulent Phage Lyses host ? death of host cell

38. The lytic cycle of phage T4

39. Lytic and Lysogenic reproductive cycles of phage ?, a temperate phage

40. The reproductive cycle of an enveloped Virus RNA viruses RNA serves as template to produce mRNA e.g. viruses that cause rabies, measles, mumps, flu DNA viruses DNA serves as template to produce mRNA Herpes (Cold sores, genital herpes) Smallpox Adenovirus

41. AIDS: Acquired Immunodeficiency Syndrome

42. HIV infection

43. AIDS around the world (Source: UNAIDS)

45. Animation of HIV Life Cycle Questions to Address: Why does HIV infect a specific cell type, T-helper cells (CD-4 cells)? What is HIV?s Genetic material? What are the roles of Reverse Transcriptase, integrase, and protease? How can knowledge of HIV?s life cycle be used to develop anti-HIV treatments? Reverse Transcriptase does not ?proof read? like DNA polymerase does. What are the consequences? Of what adaptive value is this?

47. Overview of HIV?s Reproductive Cycle

49. Vaccines have been unsuccessful?why? Reverse Transcriptase Inhibitors ? Block viral DNA formation from viral RNA DNA base analogs ? Block DNA elongation e.g. AZT, 3TC (3-thiocytosine) Protease Inhibitors ? Block enzymes that process envelope proteins Why use a ?Shotgun? approach? Possible future treatments: Plug drugs?drugs that plug receptors for HIV on surface of host cell Vaccines

50. Evolutionary Origin of Viruses Evolved from fragments of Cellular Nucleic Acids Evidence Viral genetic material similar to host cells genetic material Some viral genes are identical to host?s genes Eukaryotic viral genetic material is quite different to prokaryotic and phage genetic material Eukaryotic viral genetic material is similar to transposons (?jumping genes?) Transposons: highly mobile eukaryotic genetic material Phage DNA is similar to Plasmid DNA Plasmid DNA: highly ?mobile? extra-chromosomal circular DNA found in bacteria

51. Lysogenic Conversion Lysogenic Conversion Expression of prophage genes to produce toxins Botulism Bacterium ? neurotoxin (coded by prophage) ? paralysis ? death Are antibiotics effective against botulism poisoning? Scarlet Fever Bacterium ? toxin (coded by prophage) ? sore throat, strawberry-colored tongue, rash ? death Give antibiotics within 3 days


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