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Virus Demo

Learn about the components of a virus, the differences between lytic and lysogenic cycles, and how viruses can introduce genetic variation into host organisms. Explore the properties of viruses and bacteria, and discover how they are classified. Understand the reproductive cycles of viruses and their impact on host cells. Gain insights into the defense mechanisms of bacteria against viruses. Explore the concept of emerging viruses and current outbreaks.

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Virus Demo

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  1. Virus Demo

  2. Viruses Chapter 19

  3. What you must know: • The components of a virus. • The differences between lytic and lysogenic cycles. • How viruses can introduce genetic variation into host organisms. • Mechanisms that introduce genetic variation into viral populations.

  4. Properties of a Virus

  5. Bacteria Virus • Prokaryotic cell • Most are free-living (some parasitic) • Relatively large size • Antibiotics used to kill bacteria • Not a living cell (genes packaged in protein shell) • Intracellular parasite • 1/1000 size of bacteria • Vaccines used to prevent viral infection • Antiviral treatment Bacteria vs. Viruses

  6. Parts of the Virus

  7. Components = nucleic acid + capsid • Nucleic acid: DNA or RNA (double or single-stranded) • Capsid: protein shell • Accessory Structure: Some viruses also have viral envelopes that surround capsid • Found in many animal viruses • Pick up bits and pieces as they travel from host to host. Introduces genetic variation (Transduction).

  8. Breaking all of the rules • Mimivirus (Giant virus) 400 nm • 1.2 million base pair • Codes 979 proteins – more than any other virus. • This treasure chest includes some proteins never found in any viral genome

  9. How are viruses classified?What is the host range?

  10. Classification • Obligate Intracellular Parasites • Specific to their hosts (human, dog, some can cross species) • They can only attack specific cells, the common cold is a virus that specifically attacks cells of the respiratory track (hence the coughing and sneezing and sniffling). HIV specifically attacks white blood cells

  11. Host Range • Limited host range • Evolution: Recognition systems in viruses • Entry = attach to host cell membrane receptors through capsid proteins or glycoproteins on viral envelope (animal) • Eg. human cold virus (rhinovirus)  CAN ONLY INFECT SPECIFIC TISSUE: upper respiratory tract (mouth & nose) • Some Broad Range (West Nile – mosquitoes, horses, humans, birds)

  12. Simplified viral replicative cycle Entry: Tail inject genetic material, Endocytosis, Fuse with the Membrane

  13. A virus that infects a bacteria is called…

  14. Bacteriophage Virus that infects bacterial cells

  15. How do viruses reproduce? E.Bola

  16. Reproduction • Reproduce quickly within host cells • Lytic cycle - reproduction occurs, cells burstLysogenic cycle - reproduction does not immediately occur (dormancy)

  17. Lytic Cycle of T4 Phage Penetrate Maturation

  18. Lytic Cycle • Use host machinery to replicate, assemble, and release copies of virus • Virulent phages only go through the lytic cycle • Cells die through lysisor apoptosis Why haven’t phages exterminate bacteria? 3 reasons

  19. Bacterial Defense • Restriction Enzymes – cut up the viral DNA into pieces • Bacterial DNA is methylated to prevent attack of these restriction enzymes • Natural selection - favors bacteria with surface proteins that don’t recognize the phage • Lysogeny/Dormancy

  20. Lysogenic (Latent) Cycle: • DNA incorporated into host DNA and replicated along with it Temperate Phage: Capable of both Lytic/Lyso cycles (lambda) Prophage: Fuses with bacterial DNA and goes dormant • Enviromental Signal: UV radiation, chemicals: • Trigger lysogenic lytic cycle

  21. Lytic Cycle vs. Lysogenic Cycle

  22. Expression of viral genes can change host phenotypes • Secondary effects • Scarlet Fever • Botulism* • Diptheria** • Certain E.Coli strains • Release harmful toxins * Paralysis neurotoxin **Nerve inflammation, myocarditis, paralysis

  23. Animal viruses have a membranous envelope • Host membrane forms around exiting virus • Undercover, Covert operations • Difficult for host immune system to detect virus

  24. Plant Viruses • Horizontal Gene Transfer: Accidental, Non-traditional reproduction (Wind, Herbivore damage, Injury) • Vertical Gene Transfer: Generations (Cutting/Asexual, Infected Seeds)

  25. Retrovirus • RNA virus that uses reverse transcriptase(RNA  DNA) • Newly made viral DNA inserted into chromosome of animal cell (provirus) • Host transcribes provirus to make new virus parts • Examples: • HIV (Human Immunodeficiency Virus) • RNA and Enzymes • Herpes • Small pox

  26. What is the difference between a prophage and provirus?

  27. How does HIV lead to AIDs?

  28. NPR How Do Viruses Work

  29. Mutations • Can mutate easily • Lack error-checking mechanisms • Why there is no vaccine for common cold • Leads to genetic variation within virus populations

  30. Emerging Viruses • Endemic – regularly found in a certain area • Malaria of Africa • Epidemic – widespread outbreak • 2003 SARS • Pandemic – Global epidemic • Flu (waves) mutates quickly • HIV/AIDS

  31. Current Outbreaks • Zika Virus • Spread by Aedes mosquitoes (Aedes aegypti) “Arbovirus” • Major outbreak in Brazil and Latin America • Linked to birth defects (microcephaly)

  32. Zika Virus (as of Dec. 2015)

  33. As of Feb. 2016 (CDC.GOV)

  34. Drugs for Prevention/Treatment • Vaccine: weakened virus or part of pathogen that triggers immune system response to prevent infection • Ex. HPV, MMR, HepA, Flu shot • Antiviral Drugs: block viral replication/synthesis of nucleic acids after infection • Ex. Tamiflu (influenza), AZT (HIV)

  35. Where did the first viruses come from? Observation 1. Share cell properties Observation 2. Infect all life forms Theory: Arose after first cells Escaped bits of nucleic acids (plasmids) Infect humans and bacteria with same mechanisms -Mix match of parts *Small circular DNA molecules found in bacteria and yeast

  36. Viroids • Small, circular RNA molecules that infect plants • Cause errors in regulatory systems that control plant growth • Cadang-Cadang: 10 mil: Coconut palms in Philippines

  37. Prions • Misfolded, infectious proteinsthat cause misfolding of normal proteins • Mad cow disease (BSE) • Can be transmitted by food and cause neuro degeneration • Slow acting (10 years) • Can’t be denatured, no cure

  38. Prion Neurodegenerative Diseases • Alzheimer’s Disease • Parkinson’s Disease

  39. Video: HIV Life Cycle

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