Pre-quiz  1. Why did it take so long to discover viruses?  2. Of what are viruses made?  3. What assists viruses in infecting foreign Cells?  4. Are viruses Alive?  5. Why do viruses need a host?

Pre-quiz  6. Are viruses made of DNA or RNA?  7. How do the Lytic and Lysogenic cycle differ?  8. Why is it called a retro-virus and give an example?  9. How does a vaccine work  10. What’s the difference between an epidemic and pandemic?

 Viruses unclassified until 1935  TMV ( Tobacco Mosaic Virus)

 American Scientist Wendell Stanley Crystallized TMV  1935 first SEM pictures taken

Structure of Virus  Nucleic Acids  Enclosed in protein coat  Sometimes membranous envelope

 Capsid- protein shell enclosing viral genome

 Viral envelopes derived from host cell.  Contain phospholipids and host proteins

 Bacteriophages or phages  Attack bacteria  Guess which bacterial phages were first studied.

Hosts  Host Range  Can be very general or very specific  Based on Shape  Lock and Key analogy

Why do viruses need host?  What are they made of?  Still need other parts required for ATP and Replication, and protein synthesis

Lytic Cycle Lysogenic cycle  Lyses the cell  Virulent Phage  Does not destroy cell  prophage Temperate Phages

Lytic Cycle

Lytic cycle

Lytic Cycle

Lytic cycle

Temperate Phage

Animal Viruses  Envelope allows to infect animal  DNA vs. RNA  Double Stranded vs. Single Stranded

Enveloped RNA Virus Herpes

Retrovirus

HIV

Use your book to compare and contrast : Viruses, Viroids, Prions

 Of what are viruses made?  Why do viruses need a host?  How do the Lytic and Lysogenic cycle differ?  Why is it called a retro-virus and give an example?  What is the difference between a Prion, and viroid?