1. Viruses
Chapter 10.17

2. What you need to know! The components of a virus.
The differences between lytic and lysogenic cycles.

3. What’s a Virus? Not a living cell but an infectious particle
Obligate intracellular parasite
Contains:
nucleic acids
protein coat

4. Viruses are Tiny

5. Protein Coats-Capsids
Capsids are made from proteins called capsomeres
Capsids have many different shapes depending on the virus:
Rod shape, Helical, Polyhedral, Icosahedral
Some viruses will have membrane left from the host cell

6. Tabacco Mosaic Virus
Helical capsid with RNA

7. Adenovirus Respiratory virus in animal
Polyhedral capsid with glycoprotein spikes

8. Influenza virus
Membrane envelope from host studded with glycoproteins

9. Bacteriophages Viruses that infect bacteria
icosahedral shape of a phage resembles a lunar landing probe

10. Viral Genome DNA double helix Single stranded DNA Double stranded RNA
Single stranded RNA

11. Viral Reproduction Viruses are obligate intracellular parasites
Isolated viruses cannot reproduce
They lack the ribosomes and enzymes for making proteins
Viruses can only infect limited range of host

12. Lytic Cycle Virus infects host cell Cell constructs virus
Cell dies and releases the virus

14. Lysogenic Cycle Virus infects host cell
Virus nucleic acid hides inside host DNA
A stimulus triggers the virus into the Lytic Cycle

16. RNA as genetic material
Either used directly as mRNA
Or retroviruses deliver an enzyme called “Reverse Transcriptase” that converts RNA into DNA
HIV
Due to their single strand, RNA viruses mutate a lot

17. HIV – enveloped RNA Virus
Attaches only to T-cells (WBC)
Translates RNA into DNA, integration into cellular DNA called provirus
Provirus DNA is transcribed to make new HIV viruses that leave cell
Provirus never leaves cell

19. Immune Response and Vaccinations
Body produces antibodies that fit specific virus structure
Vaccination are treated versions of the virus that don’t infect and allow the immune system to develop antibodies
Example: measles , small pox, Hep B, polio