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Viruses

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Viruses

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  1. Viruses Chapter 13

  2. Viruses, Viroids and Prions Ch. 13

  3. Study of Viruses - Virology • 5 Kingdoms • 1. Plantae • 2. Animalia • 3. Fungi • 4. Protista • 5. Monera

  4. 5 Characteristics of Life • 1. Cells • 2. Grow and maintain their structure by taking up chemicals and energy from the environment • 3. Respond to their external environment • 4. Reproduce and pass on their organization to their offspring • 5. Evolve and Adapt to their environment

  5. Viruses are: • 1. Acellular • 2. Obligate intracellular parasites • 3. No ATP generating system • 4. No Ribosomes or means of Protein Synthesis

  6. Typical Virus 2 Parts • 1. Nucleic Acid • DNA or RNA (But never both) • 2. Capsid (Coat Protein) • Some Viruses: • A. Envelope • B. Enzymes

  7. Host range • Spectrum of host cells that a virus can infect • Some viruses only infect: • plants • invertebrates • protists • fungi • bacteria (Bacteriophages)

  8. Host range • Most viruses have a narrow host range • Polio virus - nerve cells • Adenovirus - cells in upper Respiratory Tract

  9. Host range is determined by Viruses ability to interact with its host cell • Binding Sites match Receptor Sites • Binding Sites - on viral capsid or envelope • Receptor Sites - on host cell membrane

  10. Viral Size 20 nm to 1,000 nm .02 u to 1 u

  11. Viral Structure • 1. Nucleic Acid • 2. Capsid (Coat Protein) • Nucleic Acid • DNA or RNA (But never both) • ssDNA • ds DNA • ss RNA • ds RNA

  12. Viral Structure • Capsid (Coat Protein) • protects viral genome from host endonucleases • capsomeres • Binding Sites • Envelope • derived from the host cell • Binding Sites

  13. Viral Morphology 1. Helical

  14. Viral Morphology 2. Polyhedral icosahedral

  15. Viral Morphology 3. Enveloped A. Enveloped Helical B. Enveloped Polyhedral

  16. Viral Morphology 4. Complex

  17. Viral Classification • 1. Nucleic Acid • 2. Morphology • 3. Strategy for replication

  18. Growing Viruses • 1. Bacteriophages • Lawn of Bacteria on a Spread Plate • Add Bacteriophages • Infection will result in “Plaques” • Clear zones on plate

  19. Growing Viruses • Animal Viruses • A. Living Animals • mice, rabbits, guinea pigs • B. Chicken Embryos (Eggs) • used to be most common method to grow viruses • Still used to produce many vaccines (Flu Vaccine) • C. Cell Cultures • Most common method to grow viruses today

  20. Cell Cultures • 1. Primary Cell Lines • die out after a few generations • B. Diploid Cell Lines • derived from human embryos • maintained for up to 100 generations • C. Continuous Cell Lines • Transformed Cells (Cancerous Cells) • may be maintained indefinitly • HeLa Cells • Henrietta Lax 1951 (Cervical Cancer)

  21. Viroids and Prions • Viroids • Naked RNA (no capsid) • 300 – 400 nucleotides long • Closed, folded, 3-dimensional shape (protect against endonucleases ?) • Plant pathogens • Base sequence similar to introns

  22. Prions • Proteinaceous infectious particle • 1982 • Diseases • Scrapie (sheep) • Creutzfeldt-Jacob disease (CJD) • Kuru (Tribes in New Guinea) • Bovine Spongiform Encephalopathy (BSE) • Mad Cow Disease

  23. Viral Replication • Bacteriophage • 1. Lytic Cycle • 2. Lysogenic Cycle

  24. Lytic Cycle • 1. Attachment- binding sites must match receptor sites on host cell • 2. Penetration - viral DNA is injected into bacterial cell • 3. Biosynthesis • Genome replication • Transcription • Translation Virus uses Host Cells enzymes and machinery

  25. Lytic Cycle • 4. Assembly (Maturation) • viral particles are assembled • 5. Release • Lysis

  26. Lysogenic Cycle • 1. Attachment • 2. Penetration • 3. Integration • Viral Genome is integrated into Host Cell Genome • Virus is “Latent” • Prophage

  27. Lysogenic Cycle • 4. Biosynthesis - Viral Genome is Turned On • Genome replication • Transcription • Translation • 5. Assembly • 6. Release • Lysis

  28. Lysogenic Convergence • 1. Corynebacterium diphtheriae • 2. Streptococcus pyogenes • Scarlet Fever • 3. Clostridium botulinum

  29. Animal Virus Replication(non-enveloped virus) • 1. Attachment • Binding Sites must match receptor sites on host cell • 2. Penetration • Endocytosis (phagocytosis) • 3. Uncoating • separation of the Viral Genome from the capsid

  30. Animal Virus Replication(non-enveloped virus) • 4. Biosynthesis • Genome Replication • Transcription • Translation • 5. Assembly • Virus particles are assembled • 6. Release • Lysis

  31. Enveloped Virus Replication • 1. Attachment • 2. Penetration • 3. Uncoating • 4. Biosynthesis • 5. Assembly • 6. Release • Budding

  32. Retro Viruses (1975) • DNA ---------> mRNA ------------> Protein • Central Dogma of Molecular Genetics Normal Virus RNA -------> DNA --------> mRNA -------> Protein Retro Virus

  33. Reverse Transcriptase (Retro)

  34. Retro Viruses • 1. Many Cancer causing viruses • 2. HIV • Human Immunodeficiency Virus • AIDS • Acquired Immunodeficiency Syndrome

  35. HIV (Human Immunodeficiency Virus) • AIDS • Acquired Immune Deficiency Syndrome • results in failure of the immune system • Death usually results from an Opportunistic Infection • HIV discovered in 1984 • By who ? • Luc Montagneir - Pasteur Institute

  36. HIV Structure Retro Virus Nucleic acid - RNA (2 strands) envelope (gp 120 binding sites) Reverse Transcriptase

  37. HIV Infection (Cellular Level) 1. Attachment HIV gp 120 binding sites must match CD4 receptor sites CD4 Receptor Sites 1. Macrophages 2. Some cells of CNS 3. T4 Helper Cells (CD4 Cells)

  38. HIV Infection 2. Penetration Viral membrane and host cell membrane merge (fusion) 3. Uncoating Capsid is removed and Viral Genome is exposed

  39. HIV Infection 4. Integration Once Viral Genome is integrated - 2 possibilities: 1. Nothing - Virus is “Latent” Virus may be latent for days, weeks, months or years Median latency time = 10 years

  40. Latent HIV provirus

  41. 2.HIV Genome can be “expressed” or “Turned On” • Once HIV Genome is “turned on” death usually results within 2 years • What causes the HIV Genome to be “turned on”? • Other infections • Stress or shock to the system • Drug abuse • Alcohol abuse • Nutrition • Exercise (Lack of or too much?) • Sunburn ? • (Herpes Simplex 1)

  42. Once HIV Genome is “turned on” • 5. Biosynthesis • Genome replication • Transcription • Translation • 6. Assembly • Virus particles are put together • 7. Release • Budding

  43. Modes of HIV Transmission • HIV is transmitted by exposure to infected body fluids • 4 Body Fluids • 1. Blood • 2. Semen • 3. Vaginal Secretions • 4. Breast Milk

  44. How are these fluids transferred from one person to another? • 1. High Risk Sexual Contact • unprotected vaginal sex • unprotected oral sex • unprotected anal sex • 2. Needles • Intravenous Drug Abuse (sharing dirty needles) • accidental needle sticks

  45. How are these fluids transferred from one person to another? • 3. Blood to Blood Contact • open sores or wounds • Transfusions • Organ Transplants • Artificial Insemination • 4. Mother to Child • placenta • as baby passes thru the birth canal • breast milk

  46. HIV and the Immune System • 1. Cellular Immune System • cells phagocytize microbes • 2. Humoral Immune System • antibodies to destroy or inactivate microbes

  47. Clinical Stages of an HIV Infection • 1. Acute Infection • Initial infection of HIV (exposure to infected body fluids) • Viremia • Fever • Headaches • Weakness • Muscle and joint aches • May last for a couple of weeks • Normal CD4 cell count 1200mm3

  48. 2. Asymptomatic Disease • CD4 cell count < 1000mm3 • Virus is “latent” inside CD4 cells • Median latency period - 10 yrs. • No signs or symptoms of illness (asymptomatic) • HIV Positive - antibodies can be detected in your blood • Seroconversion • 6 to 8 weeks

  49. 3. Symptomatic Disease • CD4 cell count < 600mm3 • Viral Genome is “turned on”, Symptoms begin to appear • What causes HIV Genome to be turned on? • Other infections • stress • shock to the system • alcohol • drug abuse • nutrition • exercise ?

  50. 3. Symptomatic Disease • Symptoms • chronic fatigue • low-grade fever • night sweats • diarrhea • weight loss • Susceptible to Infections • bacterial pneumonia • meningitis • oral and vaginal yeast infections • tuberculosis