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Viruses and Bacteria Chapters 19 & 27

Explore the world of viruses and bacteria, from their structures and host ranges to viral replication processes. Learn about viral genomes, entry, uncoating, and replication cycles. Discover the impact of viruses on animals and humans, including diseases like HIV, hepatitis, Ebola, and SARS. Dive into the complexities of viral envelopes, glycoproteins, and genetic alterations in host cells.

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Viruses and Bacteria Chapters 19 & 27

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  1. Viruses and BacteriaChapters 19 & 27

  2. Bacteria • Small • Less organized • Viruses • Even smaller • Simpler • Lacking structure • Metabolic machinery

  3. Tobacco mosaic virus

  4. Viral structure • Protein coat surrounds nucleic acids • Nucleic acid (DNA or RNA) • Linear, circular, single or double stranded

  5. Viral structure • RNA genome: • Flu, measles, AIDS, SARS • DNA genome: • Herpes, small pox, mono, hepatitis B

  6. Viral structure • Helical • Rodlike in appearance • Isometric • Spherical shaped

  7. Virus

  8. Virus

  9. Bacteriophages

  10. Bacteriophages

  11. Viral structure • Capsid: • Protein sheath surrounds nucleic acid core • Few different proteins-repeated • Envelope: • Surrounds the capsid • Made of proteins, lipids, and glycoproteins • Derived from host cell’s membrane

  12. Virus host range • All organisms are affected by viruses • Host range: • Cells suitable for a virus • Viruses replicate in only a few types of cells • Examples: • HIV affects certain WBC • Hepatitis affects the liver • Common cold virus infect lining of upper respiratory tract

  13. Virus host range • Rabies virus has a broad host range • Infects several species • Some viruses lay dormant for years • HIV or herpes • Some do not cause any problems

  14. Viral replication • Not considered organisms • Unable to reproduce independently • Lack ribosomes • Enzymes for protein synthesis • Obligate intracellular parasites

  15. General viral replication • Enter host cells • Reproduce • Viruses replicate • Host’s genetic machinery • Their genes are translated into proteins

  16. VIRUS Entry and uncoating 1 DNA Capsid Transcription and manufacture of capsid proteins 3 Replication 2 HOST CELL Fig. 19-4 Viral DNA mRNA Capsid proteins Viral DNA Self-assembly of new virus particles and their exit from the cell 4

  17. Viral replication • Phage replication • 1. Lytic cycle • 2. Lysogenic cycle

  18. Viral replication • Lytic cycle: • Virus kills infected host cell when replicating • Virulent virus: • Virus multiplies within the host • Eventually rupturing the host

  19. Bacteriophages

  20. Virulent viruses

  21. Lysogenic viruses • Incorporate viral nucleic acid into genome of the host cell • Does not kill host • Prophage: • Viral nucleic acid is part of the host genome

  22. Lysogenic Virus • Transformation: • Genetic alteration of a cell’s genome by introducing foreign DNA • Phage conversion: • Foreign DNA is from the virus

  23. Lysogenic Virus • Prophage genes can make toxins • Makes bacteria more serious • Diphtheria, botulism and scarlet fever

  24. Scarlet fever

  25. Animal Virus Replication • Viruses cause illnesses in animals • Classified according to genome • RNA or DNA • Many have envelopes (glycoproteins)

  26. Animal Virus Replication • Bind to cell membrane at receptors • Enter cell • Viral RNA used as template • Makes more viral RNA • Combines with capsid • Exits host (buds) • Encased in envelope derived from host

  27. Capsid and viral genome enter the cell Capsid RNA HOST CELL Envelope (with glycoproteins) Fig. 19-7 Viral genome (RNA) Template mRNA Capsid proteins ER Copy of genome (RNA) Glyco- proteins New virus

  28. Influenza

  29. Varicella virus

  30. Shingles

  31. Epstein Barr virus

  32. Polio virus

  33. HIV

  34. HIV • Retrovirus (“backwards”) • Transcribes an RNA template into a DNA • Reverse transcriptase • Provirus • New integrated viral DNA • Does not leave host

  35. Viral envelope Glycoprotein Capsid RNA (two identical strands) HOST CELL Reverse transcriptase HIV Reverse transcriptase Viral RNA Fig. 19-8a RNA-DNA hybrid DNA NUCLEUS Provirus Chromosomal DNA RNA genome for the next viral generation mRNA New virus

  36. HIV • Human immunodeficiency virus • 1981 • T-4 cells (CD4 cells) • Lymphocytes • Unable to fight off other diseases • Maybe asymptomatic for 10 years • AIDS (acquired immunodeficiency syndrome)

  37. Membrane of white blood cell HIV Fig. 19-8b 0.25 µm HIV entering a cell New HIV leaving a cell

  38. HIV • Symptoms • Fatigue • Weight loss • Lymphadenopathy (swollen lymph glands) • Neurological disease

  39. HIV • Opportunistic infections • Candidiasis (yeast) • Pneumocystis carinii pneumonia • Kaposi sarcoma • TB

  40. HIV

  41. HIV • Transmission • Blood • Transfusion or shared needles • Intercourse • Mother to fetus

  42. Hepatitis B • Infection of the liver • Jaundice • Decreased liver function • Contact through bodily fluids

  43. Ebola virus

  44. Ebola virus • Hemorrhagic fever • Africa • Fever, joint pain • Internal & external bleeding

  45. SARS (severe acute respiratory syndrome)

  46. SARS • Respiratory infection • Coronavirus • 2003 • China

  47. Vaccines • Inactive version of pathogen • Causes immune system to form antibodies • Hepatitis • MMR, Polio, Rotavirus • Smallpox • Diphtheria (Td)

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