1. Bacteria: Section 8.3, section 16.1– 16.7, and pg. 55
Viruses
Bacteria
Immune Response
Viruses: Section 10.17—10.21
Bacteria: Section 8.3, section 16.1– 16.7, and pg. 55

2. VIRUSES General Information:
1. “Virus” comes from the Latin word for “poison”.
2. It took approximately 52 years to discover viruses.
a. was discovered studying the tobacco mosaic disease

3. Structure of a Virus
A. Basic parts:
1. Inner core that is either DNA or RNA (not both)
2. Inner core is surrounded by a “CAPSID”
a. made of protein…also called a protein coat
b. can be complex (head, tail)
c. can be simple (rod)
d. arrangement of proteins in the capsid determines the shape
3. Some, not all, have an “ENVELOPE” that surrounds the capsid.

4. Rabies virus
Marburg virus
Ebola virus
These are bacteriophages. This is the “head, tail” structure. They attack bacteria.

5. Adenovirus-African swine fever
Polio virus
Tobacco Mosaic Virus
Foot and Mouth disease virus

6. B. VIROID
1. A small circular piece of RNA with no capsid.
2. The RNA pairs with itself to make it circular.
3. Contain only enough information to allow an RNA polymerase to copy them but not enough to make a protein message.
4. Their presense causes side effects.
a. may interfere with the plants production of ribosomes
b. shown to cause tumors on potatoes
5. Little is known about how they spread.

7. C. PRION
1. A self replicating protein
2. Causes “Scrapie” (degenerates nervous system in sheep and goats)
3. Causes Mad Cow Disease
4. Causes Creutzfeldt-Jakob disease and Gerstmann Strassler Syndrome in humans
a. neurological disease

8. D. RETROVIRUS
1. Virus with RNA and an enzyme called “Reverse Transcriptase”
2. Enters cells and enzyme copies viral RNA into DNA.
3. DNA then becomes a “provirus” (virus DNA integrated with host cells DNA)

9. E. Specificity
1. Viruses are specific in the cells they attack.
2. Plant viruses only attack plants and animal viruses only attack animals.
3. May only attack one species (polio and measles…humans only)
4. Why? host cells have receptor proteins on their membranes that give off signals. Viruses only identify certain ones.

10. III. Virus Replication – there are two ways in which viruses
III. Virus Replication – there are two ways in which viruses can reproduce.
A. The Lytic Cycle
1. discovered in the 1940’s
2. This type of replication causes an “Active Infection” – the infection occurs immediately.
3. The viruses that replicate this way are “Virulent viruses” – they kill the host cell they invade.
4. Steps:
a. Virus attaches to the cell membrane (specific)
b. Virus injects DNA into the cell
c. Virus DNA takes over the cell, telling it to replicate the viral DNA and make new capsids.
d. Capsids and DNA assemble into new viruses
e. An enzyme from the virus “Lyses” (breaks) the cell membrane, releasing new viruses.

11. D A B E C

12. B. Lysogenic Cycle
1. discovered in 1953
2. This type of replication causes a “Latent Infection” – the infection DOES NOT occur immediately.
3. Examples of this type of virus: Herpes virus, HIV,
4. Steps:
a. Virus attaches to the cell membrane
b. Virus injects its DNA into the cell
c. Viral DNA forms a circle inside the host cell
d. The viral DNA attaches to the host cell’s DNA
e. The viral DNA becomes a part of the host cell’s DNA
f. The host cell replicates by mitosis (any new cell has viral DNA in it)
g. Viral DNA pinches off of the host cell’s DNA and forms a circle.
h. This initiates the lytic cycle, therefore killing the cell.

13. A, B G C H
D, E H F