Understanding Viruses and Bacteria: Structures, Replication, and Impact

1. Viruses and BacteriaChapters 19 & 27

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

3. Tobacco mosaic virus

4. Figure 19.1

5. Viral structure • Nucleic acid (DNA or RNA) • Protein coat surrounds nucleic acids • Envelope (some viruses)

6. Viral structure • Nucleic acids • Linear, circular, single or double stranded • RNA genome: • Flu, measles, AIDS, SARS • DNA genome: • Herpes, small pox, mono, hepatitis B

7. 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

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

9. RNA Capsomere DNA Virus Capsomere of capsid Glycoprotein 18  250 nm 70–90 nm (diameter) 50 nm 20 nm Tobacco mosaic virus Adenoviruses (a) (b)

10. Membranous envelope RNA Head Capsid DNA Virus Tail sheath Tail fiber Glycoproteins 80  225 nm 80–200 nm (diameter) 50 nm 50 nm Bacteriophage T4 (d) Influenza viruses (c)

11. 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

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

13. General viral replication • Not considered organisms • Unable to reproduce independently • Lack ribosomes • Enzymes for protein synthesis • Obligate intracellular parasites

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

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

18. Phage viral replication • 1. Lytic cycle • 2. Lysogenic cycle

19. Viral replication • Lytic cycle: • Virus kills infected host cell when replicating

20. Viral replication • Virulent virus: • Virus multiplies within the host • Eventually ruptures the host

21. 1 Attachment 2 Entry of phage DNA and degradation of host DNA 5 Release Phage assembly 3 Synthesis of viral genomes and proteins 4 Self-assembly Head Tail Tail fibers

22. 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

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

24. Lysogenic Virus • Prophage genes change host’s phenotype • Can make toxins • Makes bacteria more serious • Diphtheria, botulism and scarlet fever

25. Scarlet fever

26. Phage DNA Daughter cell with prophage The phage injects its DNA. Many cell divisions create many infected bacteria. Phage DNA circularizes. Tail fiber Phage Bacterial chromosome Prophage exits chromosome. Lytic cycle Lysogenic cycle Prophage is copied with bacterial chromosome. The cell lyses, releasing phages. Prophage Phage DNA and proteins are synthesized and assembled. Phage DNA integrates into bacterial chromosome.

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

28. 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

29. 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

32. Influenza

33. Varicella virus

34. Shingles

35. Epstein Barr virus

36. Polio virus

37. HIV

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

39. 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

40. 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)

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

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

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

44. HIV

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

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

47. Ebola virus

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

49. SARS (severe acute respiratory syndrome)

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