Study questions for Topic 7-2

Topic 7: The Biology of Replication of Viruses Study questions for Topic 7-2

Study questions for Topic 7-2 (The biology of replication of viruses)

Think Questions

  1. Animal viruses adsorb to receptors on the cytoplasmic membrane of host cells. Why would our cells possess receptors that viruses could adsorb to?
  2. State the role(s) of gp120 and gp41 in the life cycle of HIV.
  3. Why does HIV primarily infect T4-lymphocytes, macrophages, and dendritic cells?
  4. Why do you think the incubation period between HIV infection and AIDS has typically been 10 years or more?
  5. Describe how a lytic bacteriophage might possibly play a role in horizontal gene transfer in bacteria.
  6. Name a human viral infection that has a life cycle equivalent to the lysogenic life cycle of bacteriophages.

Short answer questions

1. Describe how an enveloped virus accomplishes each of the following steps during the productive life cycle.

  • viral attachment or adsorption to the host cell
  • viral entry into the host cell
  • the viral movement to the site of replication within the host cell
  • viral replication within the host cell
  • viral assembly or maturation within the host cell
  • viral release from the host cell

2. Why are viruses generally very specific as to the types of hosts, tissues, and cells they are able to infect?

3. Name 4 herpes viruses that may have a latent cycle, state in what cell types they become latent, and name the diseases each cause.

4. Describe how the retrovirus HIV-1 accomplishes each of the following steps during its life cycle. (Include the following keywords in your description: gp120, CD4, chemokine receptors, gp41, capsid, RNA genome, reverse transcriptase, double-stranded DNA intermediate, provirus, polyproteins, proteases, and budding)

  • viral attachment or adsorption to the host cell
  • viral entry into the host cell
  • the viral movement to the site of replication within the host cell and the production of a provirus.
  • viral replication within the host cell
  • viral assembly or maturation within the host cell and release from the host cell

5. Name 3 types of cells HIV primarily infects and briefly explain why.

6. Strains of HIV called R5 viruses to adsorb to CD4 molecules and a chemokine receptor called CCR5. These strains of HIV primarily infect cells called _________________

7. Strains of HIV called X4 viruses adsorb to CD4 molecules and a chemokine receptor called CXCR4. These strains of HIV primarily infect cells called _________________

8. If one could destroy all of the infected white blood cells in a person infected with HIV and then reconstitute the cells by giving a bone marrow transplant from a person homozygous for a deletion mutation in their gene coding for the chemokine receptor CCR5 (he or she cannot make CCR5 molecules), describe how this might prevent HIV infection in the person receiving the transplant.

9. HIV possesses a genome of RNA. How then is HIV able to insert into the DNA of host cells and form a provirus?

10. State the median incubation period for AIDS.

11. In terms of viral load, exhaustion of the lymphopoietic system, and immune responses, briefly describe what marks the progression to AIDS.

15.  Briefly describe the following:

  • early or acute HIV infection
  • chronic HIV infection
  1. Name the 2 types of bacteriophage life cycles and state what the bacteriophage capable of each is called.
  2. Describe the 5 steps involved in the lytic life cycle of bacteriophages.
  3. As will be seen in the lab, phage typing is a technique wherein unknown strains of a bacterium are identified by using known strains of bacteriophages. How can we use a bacteriophage to identify a bacterium?
  4. We saw in the previous section that a single infected animal cell may produce 10,000-50,000 viruses yet an infected bacterium can only produce 50-200 bacteriophages. Explain this.
  5. Describe how the lysogenic life cycle of temperate bacteriophages differs from the lytic life cycle of lytic bacteriophages.
  6. What is spontaneous induction as it relates to the lysogenic life cycle?
  7. When a bacteriophage inserts its DNA into the DNA of the host bacterium, this form of the virus is called a ________________
  8. The host bacterium for a bacteriophage is called a ________________
  9. A virus capable of the lysogenic life cycle is called a __________________