1. Virus, or “Poison”  Is it alive? Not really…  Depend on cells to reproduce  obligate intracellular parasites  Inert organic particles when outside cells  Viruses for all - infect bacteria, protists, and all higher plants and animals  Infect specific cell types in host Virus size comparison at Cellsalive.com

2. Edward Jenner – 1700’s, Smallpox vaccine Vaca = Cow, noticed milkmaids immune to smallpox

3. Louis Pasteur – rabies vaccine, 1800’s

4. Wendell Stanley – crystallized TMV (Tobacco Mosaic Virus), 1900’s, showed that viruses are NOT small bacteria

5. Viruses - Structure  nucleic acid (RNA or DNA) – instructions for making proteins  protein capsid  may have plasma membrane, or envelope  Surface proteins for attachment to host cell  Little or no metabolism: Who will read the DNA/RNA and make viral proteins that assemble into a viral capsid? If a virus has an envelope (membrane), where does it come from? The host cell The host cell’s plasma membrane

6. Influenza Virus Surface proteins (protein) (nucleic acid, instructions for making proteins) (membrane from host cell)

7. Criteria used to Classify Viruses 1.Type of nucleic acid 2.Presence or absence of an envelope 3.Shape/morphology of the capsid 4.Specific surface proteins  different strains

8. Lytic Cycle: Cells lyses and releases new viral particles Viral Replication by Host Cell 2. Entry 3. Replication 4. Assembly 5. Lysis / Cytolysis 1. Adsorption

9. Lysogenic Cycle: Period of dormancy until stimulus causes lytic cycle Viral Replication by Host Cell Integration of viral DNA into host’s DNA  Provirus (in this case a prophage)

10. Viral Replication by Host Cell (compare & contrast based on lecture diagrams) Lytic CycleLysogenic Cycle 1.Viral DNA/RNA transcribed and translated by host cell 2.Cells lyse and releases new viral particles 1. Period of dormancy until stimulus causes cell to transcribe and translate viral DNA (viral DNA is incorporated into cell’s DNA) 2. Cells lyse & release new viral particles

11. Retroviruses  RNA core  Replication – cells make viral DNA from RNA (reverse order)  Enzyme: reverse transcriptase – virus contains it  Ex.: HIV and tumor producing viruses HIV inside human T 4 lymphocyte

12. Provirus (viral DNA in cell’s chromosome) Retrovirus injects RNA and reverse transcriptase enzyme into host cell; viral DNA is integrated into cell’s DNA (provirus forms) and may remain dormant for long various periods of time (lysogenic). Reverse transcriptase New retroviruses

13. (Cystic Fibrosis) Viruses can be used to insert genetic material into cells. Ex.: Gene therapy to cure genetic diseases

14. Gene Therapy for CF

15. Possible Evidence of Virus Evolution Today = Plasmid in Bacteria Today = jumping genes in Corn “Chunks” of DNA that can move around and be independent: Plasmids and Transposons

16. Viral Disease Examples  Common cold  Influenza  Rhinovirus  Smallpox (eradicated)  Chicken pox  Rabies  Polio (still out there…)  Mumps  Rubella  Ebola (90% lethality)  Lassa fever  Dengue fever  Many other hemorrhagic fevers  The list goes on and on and on….

17. Are Viruses Considered to be Living or Non-Living? CharacteristicNo, Viruses do not display this traitYes, Viruses do display this trait Nucleic Acid Growth Mutate Production of ATP Cell Organelles Homeostasis Metabolism Independent Reproduction

18. Other Infectious Particles  Viroids – single strand of RNA, no capsids Ex.: plant diseases

19. Prion causes proper proteins to fold incorrectly  cannot do their ‘job’ in the cell, collect inside cell  cell death  Prions – infectious protein molecules Ex.: CJD, scrapie, mad cow disease (BSE)

20. Prion Disease – ‘holes’ in brain tissue