MCB 229 Spring 2000 Study Guide 17 Prof. Terry

1. There's a lot of information in this chapter. Focus on answering the questions below. We will look at some general principles of animal viruses, then concentrate on 4 specific examples: Polio, Herpes, Influenza, and HIV. As you read, pay special attention to information relative to these 4 virus families.
2. Compare the host cell specificity of poliovirus and measles virus. Which cells can each virus bind to? What type of biomolecules on the cell surface are responsible for virus binding?
3. How are the following viruses classified in terms of: nucleic acid, enveloped or naked, capsid, and site of virus assembly? Herpes simplex, Smallpox/Cowpox, Polio, HIV, Influenza.
4. How does animal virus entry into host cells differ from bacteriophage entry into host cells? What are the 3 mechanisms for animal virus entry? By which mechanism is a naked virus such as polio likely to enter? By which mechanism is an enveloped virus such as influenza likely to enter?
5. What is receptor-mediated endocytosis? How does it differ from plain old endocytosis?
6. Where does DNA replication typically occur for DNA viruses? Are there any exceptions – if so, which virus(es)?
7. Where does RNA replication occur for RNA viruses? What enzyme is required before "-" RNA viruses can express genes? Where does this enzyme come from?
8. What is a retrovirus? What type of nucleic acid is found in retroviral virions? What does the enzyme reverse transcriptase do? What happens to the nucleic acid that is produced from this enzyme?
9. How are naked virions typically released from a host cell? How are enveloped viruses typically released from a host cell? For viruses that are released by "budding" out, which membrane do they bud from? Are there exceptions – if so, which virus?
10. What is meant by "cytocidal infection"? By "cytopathic effect" (CPE)? What are some common causes of CPE?
11. What is meant by the following terms: acute infection, persistent (chronic) infection, latent infection? What does a "slow virus" disease mean?
12. Can viruses cause cancer in animals? In humans? Identify at least two types of human cancers caused by viruses.
13. Skim the sections on plant, fungi, algae, and insect viruses. You will not be tested on this material.
14. What is a viroid? What organisms do most known viroids infect?
15. What is a prion? What does PrP stand for? Where is it found? Note that, although your text suggests several alternative possibilities for the mechanism of action, the "abnormal conformation" hypothesis is currently the dominant one. The presence of abnormal PrP seems to trigger a change in conformation of normal PrP into an abnormally folded one, leading to degeneration of tissues containing PrP – sort of a "domino" effect. What are some of the diseases associated with prions?
    

1. The remaining questions deal with specific viral diseases. Your text includes this material in Ch. 36. You are only responsible for specific viruses as listed below, although you may find it interesting to read through all of Chapter 36 for your own edification.
2. Pp. 739-740. What type of virus causes chickenpox and shingles? How is it transmitted? What is a typical incubation period? What tissues are infected and what are the symptoms of chickenpox? What happens to the virus after the course of infection is finished? When and how do people get shingles?
3. Pp. 740-741. What group of viruses causes influenza? How is it transmitted? What is a typical incubation period? What tissues are infected and what are symptoms of flu? What happens to the virus after the course of infection is finished? Why doesn't immunity protect you from further infections of influenza?
4. Pp. 746-752. [Note: There is much more detail in this section than you need to remember. Be able to answer the questions below – skim the rest.] What type of virus causes AIDS? Approximately how many people worldwide are currently infected? How is AIDS virus transmitted? What host tissues are infected? Study Fig. 36.10, which summarizes details of the virus life cycle. Where does conversion of RNA to DNA occur? What happens to the HIV provirus? How are new virions assembled? What is a CD4+ cell? What is considered a "normal" CD4+ cell concentration (in cells/μl)? What is the CD4+ cell level at which the CDC defines AIDS (in cells/μl)? Approximately what % of white cell population has been eliminated at this point? Approximately how long does it take from the time of initial infection to get to this CD4+ cell level? What are common causes of death in AIDS patients? What are the two types of drugs that are currently used to control AIDS?
5. Pp. 752-753 (cold sores); pp. 755-756 (genital herpes); and p. 757 (infectious mononucleosis). What virus family is responsible for these diseases? Which of these diseases can recur? What happens to the virus in between acute infectious periods? What are the symptoms of each disease? What is the incidence of each disease in the U.S. population?