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

2. History of Virus 1. Small Pox – 17th Century 2. 1798 – Edward Jenner
– Iwanowsky (TMV- contagium vivum fluidum)
– Stanley (Crystallize the TMV)
– Twort & d’Herelle (Bacteriophage)
– 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 2. Capsid (Coat Protein) Nucleic Acid
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) Envelope
protects viral genome from host endonuclease
capsomeres
Binding Sites
Envelope
Spikes (protein, carbohydrate) are present on envelop of many viruses

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 1.Host range 2.Nucleic Acid 3. Morphology
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 B. Diploid 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 (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 - Causes disease in animals and humans
- 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
CJD – Neurological disorder
Kuru – Transmitted by contact with brain and tissue of dead victims

25. Viroids and Prions Prions
Prions are protenaceous particles with Mo Wt d
Prions are now considered as responsible for many nervous system disease
Mechanism of pathogenesis and transmission is not fully understood
CJD – Neurological disorder
Kuru – Transmitted by contact with brain and tissue of dead victims

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) 5. Release
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