07 viruses


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07 viruses

  1. 1. VIRUSES
  2. 2. Viruses Yellow fever virus. The first human virus to be discovered, in 1901.
  3. 3. Viruses A seventh kingdom of life? 1. Eubacteria 2. Archaea 3. Protista 4. Fungi 5. Plants 6. Animals 7. (Viruses, Viroids, and Prions?)
  4. 4. Think. Pair. Share. What is a virus? Can you think of any examples of viruses? Are viruses living or non-living?
  5. 5. Think. Pair. Share. Which Domain do you think viruses are in? Which Kingdom do you think viruses are in? The answers are coming up!
  6. 6. Examples of Viruses • Influenza • HIV • Chicken pox • H1N1 • Rabies • Ebola • T4 Bacteriophages
  7. 7. Viruses A virus is a small infectious particle containing genetic material (DNA or RNA) within a protein capsule (capsid).
  8. 8. Viruses Viruses reproduce by inserting their genetic material into host cells and "taking them over". This makes them intracellular parasites. The general name given to a single virus particle that is not infecting a cell is "virion".
  9. 9. Viruses A virus is an obligate parasite; it requires a host cell to reproduce.
  10. 10. Viruses They are responsible for many diseases. Epidemic: Large-scale disease outbreak in a region. Pandemic: Multi-region or global disease outbreak. AIDS
  11. 11. Viruses There are many different ways viruses can be transmitted: Disease rabies HIV Transmission Method bites (saliva  blood) body fluid exchange – excluding saliva influenza, chicken pox, airborne/direct contact common cold measles, mumps direct contact
  12. 12. Viruses Viruses are non-living and are not part of the traditional taxonomic ranks. Virus Think. Pair. Share. Which properties of living things do viruses not have?
  13. 13. Viruses Viruses are acellular; they have no membranes or cytoplasm. Viruses have no metabolism they can not grow or divide. Viruses do not require nutrients or energy. They do not create waste.
  14. 14. Differences Between Viruses and Cells Genetic material: Viruses contain RNA or DNA enclosed by protein, not a membrane. Organelles: None. Life cycle: Is not alive – has no real "life cycle"
  15. 15. Differences Between Viruses and Cells Size: Viruses are much smaller than cells. Metabolism: Viruses have no metabolism.
  16. 16. Viruses Viruses can be classified into their own orders/families/genera/species based on certain properties: - size - shape - genetic material - host cells - contains DNA or RNA - single-stranded or double-stranded genetic material - presence of absence of an envelope
  17. 17. Virus Shapes - Cylindrical
  18. 18. Virus Shapes - Polyhedral
  19. 19. Virus Shapes - Spherical
  20. 20. Virus Shapes – Irregular (Phage) This bacteriophage (phage for short) is a virus that infects bacteria only. capsid (entire top part) nucleic acid tail (entire bottom part) sheath tail fibres cell membrane viral RNA/DNA injected into host cell
  21. 21. Virus Shapes Tail fibres and spikes are used to attach to host cells. Capsids and capsomeres are protective protein shells for the viruses. Envelopes are made from dead host cell membranes and allow the virus to "pretend" to be host cells and avoid detect by the immune system.
  22. 22. Infectious Cycles A virus infects a cell by inserting its nucleic acid (DNA or RNA) into it. The viral nucleic acid then enters 1 of 2 cycles: Step 1 Step 2 Step 3 Step 4 Step 5 Step 6 Lytic = steps 1, 2, 5, 6 Lysogenic = steps 1, 2, 3, 4 (5 & 6 occur later)
  23. 23. The Lysogenic Cycle Lysogenic cycle: The host cell survives, but when it divides, the virus DNA or RNA is also duplicated. Lysogenic Cycle
  24. 24. The Lysogenic Cycle There are 4 steps: Viral DNA/RNA Host Cell DNA A) Attachment & Entry
  25. 25. The Lysogenic Cycle There are 4 steps: Provirus B) Integration – viral nucleic acid becomes part of host nucleic acid Provirus: a viral section of DNA that has become part of the host cell's DNA
  26. 26. The Lysogenic Cycle There are 4 steps: C) Multiplication of genome
  27. 27. The Lysogenic Cycle There are 4 steps: D) Cell division
  28. 28. 1) Attachment virus viral DNA host DNA host cell 5) Lysis & Release - Host cell bursts open and viruses escape. 2) Insertion - Virus injects its nucleic acid into the host cell. The Lytic Cycle 3) Replication 4) Assembly - New virus particles are assembled by the host. - The host's metabolism replicates the viral parts and RNA/DNA.
  29. 29. The Lytic Cycle The lytic cycle eliminates the integration and induction of viral DNA Step 1 Step 2 Step 3 Step 4 Step 5 Step 6 Lytic = steps 1, 2, 5, 6 Lysogenic = steps 1, 2, 3, 4 (5 & 6 occur later)
  30. 30. Infectious Cycles A virus can switch back and forth between cycles and a virus may be in lysogeny for many years. Lytic Cycle Lysogenic Cycle
  31. 31. Infectious Cycles Sometimes newly formed viruses take sections host DNA with them. Transfer of genes using a virus is called transduction.
  32. 32. Vaccinations Our immune systems can create a memory for infections that we have previously fought-off.
  33. 33. Vaccinations Previously encountered pathogens (like viruses or bacteria) are much more easily destroyed. Pathogen Pathogen
  34. 34. Vaccinations Previously encountered pathogens (like viruses or bacteria) are much more easily destroyed. Pathogen Pathogen
  35. 35. Vaccinations A vaccination is a weakened pathogen that our immune systems can easily fight-off. After our bodies have learned how to combat that particular pathogen, repeat infections are more easily destroyed.
  36. 36. Think. Pair. Share. How might a virus be used to benefit humans?
  37. 37. Viruses - Benefits We can now craft viruses that contain beneficial genes or drugs within their capsids (called viral vectors).
  38. 38. Viruses - Benefits These vectors enter the target cells and deliver their DNA to create a helpful provirus: Vector Contents Drugs Copies of beneficial genes Novel (new) genes Application Ex. Chemotherapy for cancerous cells. Gene therapy (replacement or addition of new or better genes). Creation of GMOs (genetically modified organisms, like plumper fruits or leaner livestock).
  39. 39. Viroids A viroid is an infectious piece of RNA. It does not code for anything and has no protective structure like a membrane or capsid.
  40. 40. Viroids These properties make them no less destructive to vulnerable species. Normal Potatoes Infected Potatoes The potato spindle tuber viroid (PSTVd) greatly damages potato crops. The PSTVd molecule
  41. 41. Prions A prion is an infectious protein. It has no outer structure, but damages other proteins it comes into contact with. The damaged proteins may become prions.
  42. 42. Prions
  43. 43. Prions
  44. 44. Prions
  45. 45. Prions
  46. 46. Prions
  47. 47. Prions
  48. 48. Prions
  49. 49. Prions Bovine spongiform encephalopathy (BSE, mad cow disease) is caused by prions. The brain losses mass and becomes "spongy" due to destroyed/damaged proteins. Brain of animal with BSE Brain of healthy animal
  50. 50. Prions Creutzfeldt-Jakob disease (CJD) is caused by prions in human brains. It starts with memory loss and dementia, leading to loss of muscle control and death.