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Understanding Viral Genetics and Diseases: From Polio to COVID-19

Explore the fascinating world of viral genetics and diseases, including the history of epidemics like the 1918 influenza, the eradication of smallpox, the emergence of Ebola and SARS, and the mechanisms of viral infection. Learn about the viral lifecycle, host range, and the impact of viruses on human health, including the link between viruses and certain cancers.

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Understanding Viral Genetics and Diseases: From Polio to COVID-19

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  1. Chapter 18. Viral Genetics

  2. Hepatitis Viral diseases Polio Measles Chickenpox

  3. Influenza: 1918 epidemic 30-40 million deaths world-wide RNA virus

  4. Smallpox • Eradicated in 1976 • vaccinations ceased in 1980 • at risk population?

  5. Ebola SARS Emerging viruses • Viruses that “jump” host • switch species • Ebola, SARS, bird flu,

  6. A sense of size • Comparing size • eukaryotic cell • bacterium • virus

  7. What is a virus? Is it alive? • DNA or RNA enclosed in a protein coat (capsid) • Viruses are not cells • Extremely tiny • electron microscope size • smaller than ribosomes • ~20–50 nmc • 1st discovered in plants (1800s) • tobacco mosaic virus • couldn’t filter out • couldn’t reproduce on media like bacteria

  8. Variation in viruses plant virus pink eye • Parasites • Many shapes • lack enzymes for metabolism • need host “machinery”

  9. Variation in viruses influenza bacteriophage • A package of genes in transit from one host cell to another “A piece of bad news wrapped in protein” – Peter Medawar

  10. Viral envelope • Lipid bilayer membranes cloaking viral capsid • envelopes are derived from host cell membrane • glycoproteins on surface HIV

  11. Generalized viral lifecycle • Entry • virus DNA/RNA enters host cell • Assimilation • viral DNA/RNA takes over host • reprograms host cell to copy viral nucleic acid & build viral proteins • Self assembly • nucleic acid molecules & capsomeres then self-assemble into viral particles • exit cell

  12. Symptoms of viral infection • Link between infection & symptoms varies • kills cells by lysis • cause infected cell to produce toxins • fever, aches, bleeding… • viral components may be toxic • envelope proteins • Damage? • depends… • lung epithelium after the flu is repaired • nerve cell damage from polio is permanent

  13. Viral hosts • Host range • most types of virus can infect & parasitize only a limited range of host cells • identify host cells via “lock & key” fit • between proteins on viral coat & receptors on host cell surface • broad host range • rabies = can infect all mammals • narrow host range • human cold virus = only cells lining upper respiratory tract of humans • HIV = binds only to specific white blood cells

  14. Flu Attack! How A Virus Invades Your Body • https://www.youtube.com/watch?v=Rpj0emEGShQ

  15. Bacteriophages • Viruses that infect bacteria • ex. phages that infect E. coli • lambda phage • 20-sided capsid head encloses DNA • protein tail attaches phage to host & injects phage DNA inside

  16. Bacteriophage lifecycles • Lytic • reproduce virus in bacteria • release virus by rupturing bacterial host • Lysogenic • integrate viral DNA into bacterial DNA • reproduce with bacteria

  17. Lytic lifecycle of phages

  18. Lysogenic lifecycle of phages

  19. transcription translation DNA RNA protein replication Why is thissignificant? RNA viruses • Retroviruses • have to copy viral RNA into host DNA • enzyme = reverse transcriptase • RNA  DNA  mRNA • host’s RNA polymerase now transcribes viral DNA into viral mRNA • mRNA codes for viral components • host’s ribosomes produce new viral proteins

  20. Retroviruses have RNA instead of DNA • HIV is an example of lysogenic cycle • Aids is an example of lytic cycle

  21. HIV infection • HIV enters host cell • macrophage & CD4 WBCs • cell-surface receptor • reverse transcriptase synthesizes double stranded DNA from viral RNA • high mutation rate • Transcription produces more copies of viral RNA • translated into viral proteins • proteins & vRNA self-assemble into virus particles • released from cell by “budding” or by lysis

  22. Prions • Misfolded proteins • infectious • make plaques (clumps) & holes in brain as neurons die Creutzfeldt-Jakob disease “mad cow” disease

  23. HIV treatments • Because of HIV we have learned large amounts about viruses. Since we have learned about the viral lifecycle new drugs have been developed that prevent attachment, replication, viral protein production and release.

  24. I'm a Virus! (Mr. W's Virus Rap) • https://www.youtube.com/watch?v=kYf_Sl8W3qY

  25. Bozeman-Viruses • https://www.youtube.com/watch?v=L8oHs7G_syI

  26. Bonus Material!

  27. Cancer viruses • Viruses appear to cause certain human cancers • hepatitis B virus • linked to liver cancer • Epstein-Barr virus = linked to lymphoma • papilloma viruses • linked with cervical cancers

  28. Cancer viruses • Transform cells into cancer cells after integration of viral DNA into host DNA

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