1. Viruses, viroids and prions

2. What are viruses? Very small Obligatory intracellular parasites –Difficult to isolate, detect, cultivate –Somewhat like Rickettsia…

3. What are viruses? Contain genetic material –DNA or RNA Protein coat –Sometimes encased in lipids, carbs and proteins Reproduction inside living cells No metabolic enzymes –Use host enzyme –Problem for drug creators! Helical viruses Enveloped viruses Polyhedral Viruses Complex viruses

4. What is a host range? Host cells a virus can infect –Very narrow –Useful for treating diseases? Viral therapy Oncolytic viruses Range determined by cell receptor sites

5. What is a virion? One, complete, infectious viral particle –Contains Nucleic acid –DNA or RNA –Both can be double- or single-stranded Protein coat (capsid) –Classification based on type of capsid –Capsomeres: protein subunits

6. What is a virion? –Contains envelope (not all) Covers capsid Lipids, carbs, proteins Used to fuse with host PM May have spikes

7. What types of viruses are there? Helical –Rabies, ebola

8. What types of viruses are there? Polyhedral –Animal, plant, phages

9. What types of viruses are there? Enveloped –Influenzavirus

10. What types of viruses are there? Complex –Many phages –Additiona l structures

11. What are some viruses I should know? No specific epithet DNA viruses –Adenoviridae –Poxviridae –Herpesviridae Human herpes virus 1, HHV 2, HHV 3 –Papovaviridae –Hepadnaviridae

12. What are some viruses I should know? RNA viruses Picornaviridae Retroviridae –Lentivirus –Human Immunodeficiency Virus 1, HIV 2

13. Virus Identification Cytopathic effects Serological tests –Detect antibodies against viruses in a patient. –Use antibodies to identify viruses in neutralization tests, viral hemagglutination, and Western blot. Nucleic acids –RFLPs –PCR

14. Viral Replication

15. How do viruses multiply? Virus only has a few genes and proteins –All other proteins come from host cell E.g. ribosomes, tRNA, etc. –Must take over host metabolism

16. How do phages multiply? Two possibilities –Lytic cycle –Lysogenic cycle T-4 –About 100 genes –Multiplication in 5 stages Attachment Penetration Biosynthesis Maturation Release –animationanimation

17. What’s the difference between lytic and lysogenic cycles? Lytic cycle: Phage causes lysis and death of host cell. Lysogenic cycle: Prophage DNA incorporated in host DNA.

18. What else should I know about the lysogenic phase? When latent (temperate phase) –Can’t be infected with the same virus again –Phage conversion can happen C. diptheriae: produces toxin only in latent phase C. botulinum, C. cholerae and some streptococci also

19. What else should I know about the lysogenic phase? When latent (temperate phase) –Specialized transduction is possible

20. How do viruses multiply in animals like us? Attachment: Viruses attach to cell membrane. Penetration by endocytosis or fusion. Uncoating by viral or host enzymes. Biosynthesis: Production of nucleic acid and proteins. Maturation: Nucleic acid and capsid proteins assemble. Release by budding (enveloped viruses) or rupture.

21. What’s different about entry? Attachment first –Sites vary from person to person Penetration –Q: how does it happen in phages? –Pinocytosis OR –Fusion (animation)animation HIV Uncoating –by viral or host enzymes Figure 13.14a

22. What are the final stages for multiplication in animal viruses? Maturation –Nucleic acid –Capsid proteins Release –budding (enveloped viruses) or animation –Rupture

23. Multiplication of DNA Virus Figure 13.15

24. Pathways of Multiplication for RNA-Containing Viruses Figure 13.17

25. Multiplication of a Retrovirus PLAY Animation: Viral Replication Figure 13.19

26. DNA and RNA transcriptase DNA, reverse transcriptase: Cellular enzyme transcribes viral DNA in nucleus; reverse transcriptase copies mRNA to make viral DNA. RNA, reverse transcriptase: Viral enzyme copes viral RNA to make DNA in cytoplasm.

27. Viruses and disease

28. Is there a connection between viruses and cancer? Yes! Oncogenic viruses –10% of all cancers –DNA integrates into host cell –Tumor-specific transplantation antigen (TSTA) –Cytopathic changes

29. Can you give me some examples? HPV—cervical cancer Adenoviridae—adenocarcinoma Herpesviridae –Epstein-Barr (EB) virus—Burkitt’s lymphoma –HHV-8—Kaposi’s sarcoma Hep-B—liver cancer

30. Do all viral infections causes symptoms immediately? No Latent period for many –EB may be latently carried in 9 out 10 people –Herpesviruses can stay for lifetime Cold sores –Chickenpox—shingles (zoster) Persistent infections for some –Usually fatal –Gradual appearance and worsening of symptoms –Subacute sclerosing panecephalitis (from measles)

31. What are prions? Not viruses Infectious proteins Inherited and transmissible by –Ingestion –Transplant –surgical instruments Mad Cow Disease –Creutzfeldt-Jacob disease