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MCDB 1030
Spring 2005
Homework Set 3
Viruses and The Immune System
1. What kinds of nucleic acids may be found in viruses?
2. What is the difference between a + strand and a – strand of RNA?
3. Describe the principle events that occur in the life cycle of a + strand RNA virus.
4. What do the following enzymes do? In each case, indicate the type of organism in which the
enzyme is required. (For viruses, specify the type of virus.)
a) RNA-dependent DNA polymerase
b) RNA-dependent RNA polymerase
c) DNA-dependent DNA polymerase
d) DNA-dependent RNA polymerase
5. Summarize the first, second, and third lines of defense against invading pathogens.
6. What is phagocytosis? Why is it important?
7. The complement system contributes to destruction of bacteria in three important ways. What
are they?
8. What is inflammation? Is it beneficial or harmful?
9. Define the following terms:
a) antigen
b) humoral immunity
c) cell-mediated immunity
d) interferon
e) lymph
10. Diagram an antibody molecule and label the heavy and light chains, and the constant and
variable regions. Draw a cartoon of two antibodies that are specific for molecules of
different shapes, and show why they would not cross-react.
11. What are the roles of each of the following in the immune response?
a) helper T cells
b) cytotoxic T cells ( a.k.a. killer T cells)
c) B cells
d) Cytokines
e) MHC proteins
f) Antigen-presenting cells
g) CD4 receptor
h) CD8 receptor
12. Why are both humoral immunity and cell-mediated immunity important for fighting a viral
infection?