1. Chapter 18.2 – Viruses & Prions I.What is a Virus? A.a nonliving strand of genetic material within a protein coat 1.It doesn’t fit the criteria for life 2. Viruses need a host cell to replicate 3. Bacterio- phage: virus that infects a bacterium

2. II.Viral Structure A.Particle made of DNA or RNA – contains info for replicating the virus B.Nucleic acid is enclosed in a protein coat, called a capsid C.Some viruses have an envelope made of the same material as a cell membrane  it makes the virus easily hidden!

3. III.Viral Replication:A.Lytic Cycle – kills cells instantly 1.Attachment 2.Entry 3.Replication 4.Assembly 5.Release B.Lysogenic Cycle – cells live for a while 1.Attachment 2.Entry 3.Provirus formation 4.Cell Division

4. Lytic Cycle Lysogenic Cycle

5. IV.Viral Diseases A.Lytic – symptoms start immediately 1.Measles, Mumps, Rubella (MMR) 2.Polio 3.Ebola 4.Influenza

6. 5.Cowpox, Smallpox B.Proviruses – at ANY time, a provirus can be activated and enter the lytic cycle (usually w/ physical or emotional stress) 1.Herpes Simplex I – cold sores 2.Herpes Simplex II – genital sores 3.Hepatitis B – damages liver

7. 4.Chicken Pox – some proviruses remain in nerve cells, later causing Shingles 5.HIV - a failing immune system: 1 st – few wbc’s are infected 2 nd – more wbc’s infected = AIDS

8. V.Prions – proteins that cause infection or disease A.Diseases: 1.Mad Cow Disease (cattle) 2.Creutzfeldt-Jakob Disease (humans) 3.Scrapie (sheep) 4.Chronic Wasting Disease (deer, elk)

9. B.Prion Infection 1.Prions normally exist in cells 2.Mutated prions become folded, infect nerve cells, & cause them to burst, leaving empty spaces in the brain (“spongiform” diseases)