1. difficult to interpret, understand, or explain
Viruses
Enigmatic
en·ig·mat·ic
difficult to interpret, understand, or explain
pg. 330

2. I. Structure A. Viral Genome - Depending on the virus, may be:
1. double, or single, stranded DNA or RNA
 a virus is called either either a DNA or RNA virus
2. the nucleic acid molecule may:
a. be linear or circular
b. have multiple copies (2 is common for this type of virus)
c. be in fragments (ex: influenza virus)
3. Number of genes = 4 to 300
*verses Human genome = 30-40K genes

3. B. Capsids and Envelopes
1. Capsid - Protein coat that encloses the genome
a. built from a large number of protein subunits called capsomers
2. Envelope - membrane that cloaks some viral capsids
a. derived from host cell membrane which is modified by the virus to include membrane proteins and glycoproteins of viral origin
b. some viruses carry viral enzymes within the capsid
c. helps viruses infect their host

4. H I V
p. 336

5. II. Viral Replication A. Viruses can only reproduce within a host cell
1. obligate intracellular parasite
2. broad or narrow range of host cells
a. broad range - can infect several species
(e.g. swine flu and rabies)
b. narrow range - one species or one cell type
(e.g. phages of E. coli, HIV, Rhino virus)
Click the box to view a diagram of a phage inserting its DNA into a bacterial cell

6. Bacteriophage

7. B. Common to all viruses
1. Infect host cell with viral genome
2. Use host cell’s resources to:
a. replicate viral genome
b. manufacture capsid protein
3. Assemble progeny virus within the host cell
a. spontaneous process called self-assembly
b. last step before host cell is lysed and progeny are released
C. Retroviruses
a. RNA virus that reproduces by transcribing its RNA into DNA and then inserting the DNA into the host genome
b. to be copied every time the host cell divides
c. activated to build viruses in response to some stimulus

8. D. Three possible patterns of viral genome replication
1. DNA DNA
(uses host DNA polymerase)
2. RNA RNA
(viral genome codes for RNA replicase)
3. RNA DNA RNA*
(viral genome codes for reverse transcriptase)
* replication pathway for retroviruses

9. Figure 18.7 pg. 336 The life cycle of HIV, a retrovirus
numbered captions
are very important

10. click here for a video of HIV replication
T-Cell membrane
Attachment
Entry
Budding (Exit)
Capsid!
pg. 336
click here for a video of HIV replication

11. III. HIV: A Retrovirus A. Two classes: HIV-1 and HIV-2
1. variants of each type exist
B. Infects cells of the immune system
1. macrophages
2. helper T cells (HIV-1 and HIV-2)
3. certain B lymphocytes
4. occasionally infects glial cells in the brain
*small phagocytic brain cells which are the source of gliomas

12. C. Post incubation in the lymph nodes:
1. HIV begins to infect high numbers of T cells
2. serious decline in cell-mediated immune response
3. AIDS diagnosis = helper T cell count of 200 cells per ml. vs. > 800 cells/ml (normal)

13. Stages In HIV/AIDS Disease Progression
pg. 920 (fig. 43.2)

14. The End