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2015-02-15 22:14:18
Unit 1, Lecture 3
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  1. Infectious agents want to:
    survive, better for them to cause long term infection than to kill host
  2. Structure of Viruses?
    • 1. Protein coat = capsid
    • 2. Nucleic Acid Genome (RNA or DNA)
    • 3. Membrane/ Envelope
  3. Infectious agents want to:
    survive, better for them to cause long term infection than to kill host
  4. Decrease of infectious diseases thanks to:
    • - Progress of sanitation
    • - Vaccinations
    • - Discovery of antibiotics
  5. Epidemiology= study of?
    Study of disease in populations
  6. Epidemic
    Occurrence of disease in unusually high numbers in a localized population
  7. Pandemic
    A worldwide epidemic
  8. Endemic
    Disease is constantly present (at a low rate)
  9. The 3 Plague Pandemics
    • 1. Justinian Plague (5th-7th)
    • 2. Black Death (13th-15th)
    • 3. Modern Plague (1870s-)
  10. Black Death caused by a ______, flu caused by a ______
    Bacteria; Virus
  11. How much of European population died from Black Death?
    1/3 (1346-1353)
  12. John Snow, "The Disease Detective"
    • - founding father of epidemiology
    • - identified source of cholera episode in London & located it to a public water pump
  13. Stages of water treatment
    Sedimentation > Coagulation > Filtration > Chlorination > Storage >Distribution
  14. What is the interest of the infectious agent?
    • - Wants to survive
    • - Advantageous for it to cause a long term infection than to kill it's host
  15. Chronic Infection =?
    Long term infection
  16. The most dangerous pathogens to humans are:
    • - emerging pathogens, for which resistance has not been developed
    • - pathogens that are not dependent on human host for survival
  17. Host/Pathogen Balance
    Co-evolution of pathogen and its host until a steady state has been reached
  18. Myxoma Virus
    • - Introduced into Australia in 1950 to limit rabbit population
    • - only effective for a short amount of time, after a few years the rabbits developed resistance
  19. How did they know TMV was not caused by bacteria?
  20. Beijerinck & Stanley
    • -Beijerinck- TMV is caused by something smaller than a bacterium
    • -Stanley- isolated TMV, a nucleoprotein particle
  21. Structure of Tobacco Mosaic Virus
    • Rod-shaped protein capsid, with RNA inside
  22. Structure of Viruses
    • 1. Nucleic acid genome
    • 2. Protein coat = capsid
    • 3. Membrane/ Envelope
  23. What kind of genome can a virus have?
    DNA or RNA (double or single stranded)
  24. Why can we not build a tree of viruses like other organisms?
    Because there is no single gene that is conserved in every virus
  25. Rous Sarcoma Virus (RSV) — how many genes, what does it cause, discovered by?
    • - discovered by Peyton Rous
    • - only consists of 4 genes
    • - can cause tumors
  26. What are megaviruses?
    • - extremely large genomes (1,000+ genes)
    • - don’t cause disease in humans, found in amoeba
  27. How many genes does a pandoravirus carry?
    2,500 genes
  28. Mimivirus — nickname, number of genes, size, structure, what does it infect?
    • - mimicking microbe
    • - 900 genes
    • - close to size of bacterium
    • - protein capsid, genome inside, fiber layer around it
    • - only affects amoeba
  29. What are capsids made of and what do they contain?
    • - made of protein subunits called capsomeres
    • - contain genome of virus inside
  30. Possible shapes of capsids and examples
    • - Rod-shaped/helical (TMV)
    • - Icosahedral (adenovirus)
  31. Icosahedral Viruses — structure and example
    • - repetition of proteins in a defined geometric structure
    • - glycoproteins on its surface, extending from vertices
    • - ex: HPV, HIV
  32. Purpose of membranous envelopes in viruses?
    • - facilitate fusion
    • - way to remain undetected/ fool host’s immune system
  33. What are the membranous envelopes made of?
    • - Phospholipid bilayer
    • - contain proteins, usually from host
  34. The 2 ways a virus can deliver DNA into cytoplasm of host cell?
    • 1. inject it into cell like a syringe
    • 2. rely on fusion with host membrane
  35. Influenza Virus/Flu — genome, type of capsid, structure
    • - RNA genome, separated into 8 pieces
    • - helical capsid, circular
    • - glycoproteins on its surface
  36. What is special about the genome of the Influenza Virus? Why?
    • - It is separated into 8 pieces, not in one whole piece
    • - important because it allows for re-assortment of different pieces, which promotes variability of virus
  37. Why is it difficult to make a vaccine for the Flu?
    - very variable shape and size, always mutating
  38. Main mission of viruses?
    Make as many viruses as possible and infect as many cells as possible
  39. 3 main steps of viral reproductive cycle?
    • 1. replication of genome
    • 2. synthesis of viral structures
    • 3. process of self-assembly
  40. 3 properties of viruses related to reproduction?
    • - obligate intracellular parasites (only within host cell)
    • - disassemble during their reproductive cycle
    • - host range (broad vs. narrow)
  41. Viruses with broad host range
    • - West Nile Virus
    • - Influenza
  42. Viruses with narrow host range
    • - measles
    • - HIV
    • - SIV
  43. Viral Reproductive Cycle of a DNA Virus:
  44. Viral proteins are synthesized by the?
    host cell
  45. What are retroviruses? (example)
    • - a class of RNA viruses
    • - use reverse transcriptase to convert RNA to DNA
    • - Ex: HIV
  46. Who provides the reverse transcriptase?
    the retrovirus, not the host cell
  47. What is HIV?
    the retrovirus that causes AIDS
  48. Structure of HIV? (genome, enzymes, capsid)
    • - genome: two identical strands of RNA
    • - everything enclosed inside capsid
    • - glycoproteins on surface
    • - enzymes inside capsid: reverse transcriptase, integrase
    • - surrounded by membrane that comes from host
  49. What enzyme is needed for HIV’s DNA to integrate into host genome?
    enzyme called integrase
  50. HIV Reproductive Cycle
    • 1. Fusion of viral envelope with host membrane
    • 2. Capsid disassembles
    • 3. Reverse transcription of viral RNA into DNA
    • 4. Viral DNA is integrated into nucleus and into chromosomal DNA
    • 5. transcription/translation of genes into proteins
    • 6. Synthesis of viruses
    • 7. Exit from cell
  51. What is a provirus?
    Viral DNA that has been integrated into chromosomal DNA of host cell
  52. When did HIV start to become a huge problem?
    In the 1980s
  53. What happens is HIV infection is left untreated?
    # of T lymphocytes with drop, immune system will decrease in functioning -> AIDS
  54. Why is HIV so powerful?
    because it attacks immune system of the host
  55. What is AZT? What does it do?
    • - an analog to thymidine, instead of hydroxyl group there is an azido group
    • - prevents further synthesis of DNA from RNA by interrupting polymerization
  56. Can AZT cure HIV?
    • - No, it only helps delay its resistance and prevent the appearance of viruses
    • - must be taken in combination with other drugs
  57. Vaccines vs. Drugs
    • - antiviral drugs can help to treat viral infections (not cure)
    • - vaccines can prevent viral infections
  58. What do antibiotics work against?
    Bacteria, not viruses
  59. How do vaccines work?
    • - educates the immune system to be able to respond to certain type of infectious agent by helping it make antibodies to fight it
    • - help acquire memory against a specific pathogen
  60. One way a vaccine can be made
    • - find a similar virus to the one that causes a disease, mimic virus, can acquire resistance
    • - Ex: for smallpox, used cowpox to help humans acquire resistance against smallpox
  61. What virus is smallpox caused by?
    the double stranded DNA virus called Variola Major
  62. What is smallpox?
    • - highly contagious
    • - causes severe skin lesions
    • - invades and damages internal organs
  63. Smallpox was considered to be _______
    most devastating of all infectious diseases
  64. Why was it easier to get rid of smallpox?
    Because it was caused by double stranded DNA, which doesn’t mutate as much as a retrovirus
  65. When was smallpox declared eradicated?
    in 1979, by the WHO
  66. Who created the smallpox vaccine and how?
    • - Edward Jenner
    • - noticed that milkmaids didn’t get smallpox, they were immune to it because they had already gotten cowpox (not as severe)
    • - tested this idea on a young boy & it worked!
  67. What was Louis Pasteur known for?
    • - experimented with anthrax vaccine, gave immunity to a herd of sheep (but anthrax doesn’t really affect humans)
    • - then prepared vaccine for rabies
  68. How did Pasteur prepare vaccine for rabies & test it?
    • - left virus in dry air so that it lost some of its virulence, it could then be transferred to dogs without proving fatal
    • - tested his vaccine on Joseph Meister, 9 year old who was bitten by a dog
  69. Main difference between viroids and prions?
    • -Viroids: circular RNA molecules that infect plants and disrupt their growth
    • - Prions: infectious proteins that cause brain disease in mammals
  70. How do prions work?
    • - normal conformation and prion version
    • - prions convert normal proteins into prions
    • - which can generate plates in the brain and prevent normal functioning
  71. What is a bacteriophage? also known as?
    • - virus that infects bacteria
    • - aka T4
  72. Structure of bacteriophage
    • - capsid head, with DNA inside
    • - tail that injects DNA into host
    • - tail fibers attach to exterior of host cell
  73. Who was part of the Phage group?
    Max Delbrück, Salvador Luria, Alfred Hershey
  74. Describe Lysogenic Cycle
    • - genome is integrated into host genome, resulting in a prophage
    • - whenever host DNA is replicated, so is viral DNA
    • - continues for generations until cell experiences stress or dies
  75. Describe Lytic Cycle
    • - only use host cell to make more phages
    • - phages are made and released
    • - results in death of host cell
  76. Vertical vs. Horizontal Gene Transfer
    • - vertical: from mother to progeny
    • - horizontal: from one cell to another (can happen between species)
  77. As horizontal gene transfer increases, ________ increases
    • bacterial diversity
    • responsible for the branches in trees
  78. 3 modes of horizontal gene transfer
    • 1. Conjugation
    • 2. Transduction
    • 3. Transformation
  79. How does conjugation work? What does it rely on?
    • - requires physical contact between bacterial cells
    • - relies on plasmids and pilli
    • - genome travels to recipient through pilus tube
  80. What is needed to have genes needed to make pilli?
    the fertility factor/F factor
  81. How to tell difference between donors and recipients in conjugation?
    • - F+ strains are donors
    • - F- strains are recipients
  82. How does transduction work? What does it rely on?
    • - phages carry prokaryotic genes from one host cell to another
    • - results from accidents that occur during replicative cycle
    • - relies on phages to transfer genetic info
  83. How does transformation work? What does it rely on?
    • - uptake of foreign DNA from a cell’s surroundings
    • - relies on specific state of cell (competent state)
  84. Describe conjugation experiment don’t by Lederberg & Tatum
    • - took two different auxotrophic bacteria and combined them to see if progeny would bring new phenotype
    • - daughter bacteria was able to synthesize all 5 compounds!
    • - in order to prevent this from happening they had to put a physical barrier between the bacteria
  85. What does it mean to be auxotrophic?
    unable to synthesize certain compounds, cannot grow in minimal medium
  86. Process of transduction:
    • 1. chromosome from donor is broken up
    • 2. piece of donor DNA is incorporated into phage head
    • 3. DNA from donor is injected into recipient
    • 4. recombination occurs