Questions For Chapter

1 The data in the table below show the results of attempting to infect three different cell lines with La Crosse encephalitis virus (LAC). With electron microscopy, observations were made to detect virus particles on the surface of the cells and virus particles present in endocytotic vesicles (endosomes) inside of the cell. A "+" indicates that the virus was present in the majority (>80%) of the cells observed, whereas "+/-" indicates that the virus was present in only a few (<5%) of the cells observed. In addition, the average yield of virus per cell was measured. Using these data, answer the following questions about these cell lines.

Data for La Crosse encephalitis virus

Cell line

Virus on surface

Virus in endosomes

Virus yield per cell













  • a) Which cell lines are susceptible to infection by LAC? Why?
  • b) Which cell lines appear to be permissive for LAC infection? Why?
  • c) Propose a hypothesis to explain the data for HeLa cells compared to BHK-21 cells. How can you explain the difference in average yield per cell? How would you test your hypothesis?

2 You isolate virus particles and resuspend them in 2 ml of a buffered solution containing a total of 6 X 109 latex beads. After doing laborious and careful dilutions, shadowing, and other things necessary for electron microscopic examination, you view a number of equal fields and determine that you have 3 beads for every 9 virions. What is the approximate number of virions present in each milliliter of your beginning stock solution?

3 What features of the electron microscope make it an excellent tool for examining virus particles?

4 How would you determine the number of virion particles in Question 2 that are actually infectious (particle : PFU ratio)?

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