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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
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
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 serves as template to produce mRNA
Herpes (Cold sores, genital herpes)
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
50. Evolutionary Origin of Viruses Evolved from fragments of Cellular Nucleic Acids
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
Bacterium ? neurotoxin (coded by prophage) ? paralysis ? death
Are antibiotics effective against botulism poisoning?
Bacterium ? toxin (coded by prophage) ? sore throat, strawberry-colored tongue, rash ? death
Give antibiotics within 3 days