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

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

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

Relative Sizes

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

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

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

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

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

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)

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

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

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

Viral Morphology – Capsid Symmetry 3. Complex

Enveloped Virus

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

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

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

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

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 1951 (Cervical Cancer)

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

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

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

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 CJD – Neurological disorder Kuru – Transmitted by contact with brain and tissue of dead victims

Viral Replication Bacteriophage 1. Lytic Cycle 2. Lysogenic Cycle

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

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

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

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

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

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

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

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