Understanding Viruses, Viroids, and Prions In-depth

1. Viruses, Viroids & Prions Dr. Bhavesh Patel Principal V.P. and R.P.T.P. Science College Vallabh Vidyanagar Email – bhavesh1968@rediffmail.com

2. History of Virus • 1. Small Pox – 17th Century • 2. 1798 – Edward Jenner • 3. 1892 – Iwanowsky (TMV- contagium vivum fluidum) • 4. 1935 – Stanley (Crystallize the TMV) • 5. 1915 – Twort & d’Herelle (Bacteriophage) • 6. 1980 – Small pox had been eradicated

3. Study of Viruses - Virology • 1. Virus – Latin – Venom or Poison • 2. Acellular • 3. Obligate intracellular parasites • 4. No ATP generating system • 5. No Ribosomes or means of Protein Synthesis • 6. Akaryotic

4. Relative Sizes

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

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

7. Host range • Most viruses have a narrow host range • Polio virus – Nervous System • Adenovirus - Upper Respiratory Tract • Hepatitis Virus – Liver • Herpes Virus – Skin

8. 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

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

10. Viral Structure • 1. Nucleic Acid (NA: Protein = 1:50) • 2. Capsid (Coat Protein) • Nucleic Acid • Viruses has few thousand to 2.5 lac bp as in comparison to this E. Coli has 40 lac bp. • DNA or RNA (But never both) • ss DNA – Papova, M13, fd phages • ds DNA – Herpes, Adenovirus, Vaccinia, Smallpox • ss RNA – Picorna, Rabies, Retrovirus, Influenza • ds RNA – Bacteriophage (phy 6)

11. Viral Structure • Capsid (Protein, Lipid, Carbohydrate) • protects viral genome from host endonuclease • capsomeres • Binding Sites • Envelope • Spikes (protein, carbohydrate) are present on envelop of many viruses • Binding Sites

12. Viral Morphology – Capsid Symmetry 1. Helical – TMV, Influenza, Rabies, Measles, Mumps

13. Viral Morphology – Capsid Symmetry 2. Polyhedral – icosahedral - T phages head

14. Viral Morphology – Capsid Symmetry 3. Complex

15. Enveloped Virus

17. Viral Nomenclature • Genus name ends with Virus • Family name ends with Viridae • Order name ends with ales Host range – organ affected • Polio Virus – Nervous system virus • Herpes Virus – Skin Virus • Hepatitis Virus – Liver Virus

18. Viral Classification ICTV (1966) grouped virus in to families based on – • 1.Host range • 2.Nucleic Acid • 3. Morphology • 4. Strategy for replication

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

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

21. 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)

22. Viroids and Prions • Viroids • 1967 first viroids was identified as Potato Spindal Tuber Viroid (PSTV) • PSTV cause disease in potato • PSTV also causes disease in other members of solanaceae with difference in symptoms. • PSTV is infectious which mainly spreaded by mechanical injury, pollen grain or seed

23. Viroids and Prions • Viroids • Naked low mw, ds RNA (no capsid) • 300 – 400 nucleotides long • Closed, folded, 3-dimensional shape (protect against endonucleases ?) • Plant pathogens (do not affect animal) • Base sequence similar to introns • Probably it is an undeveloped virus originated from cellular RNA

24. Viroids and Prions • Prions - Different then Virus and Viroids - Causes disease in animals and humans - Proteinaceous infectious particle - Kuru (1957) was the first disease caused by Prions in children and Female - Scrapie (1957) was the similar disease found in sheep that affect nervous system - Creutzfeldt-Jacob disease (CJD) - Bovine Spongiform Encephalopathy (BSE) Mad cow disease

25. Viroids and Prions Prions • Prions are protenaceous particles with Mo Wt 27000-30000 d • Prions are now considered as responsible for many nervous system disease • Mechanism of pathogenesis and transmission is not fully understood

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

27. 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

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

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

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

31. 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

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

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

34. Thanks Q & A