1. Would transduction or conjugation be the most likely mechanism of gene transfer from a Gram-negative to a Gram-positive organism? Explain the reason for your answer.
2. A filter capable of preventing passage of bacteria is placed at the bottom of a U tube to separate the two sides. Streptomycin-resistant cells of a bacterium are placed on one side of the filter and streptomycin-sensitive cells are placed on the other side. After incubation for 24 hours, the side of the tube that originally contained only streptomycin-sensitive cells now contains some streptomycin-resistant cells. Give three possible reasons for this observation. What further experiments would you do to determine the correct explanation?
3. A suspension of phage when added to a culture of bacteria lyses the cells. When a suspension of the same phage is added to bacteria that have been previously agitated in a blender, no lysis occurs. Explain.
4. Is it surprising that most phages are temperate and not virulent? Explain.
5. Explain how the study of virus host range led to the biotechnology revolution. (Hint: it involves gene cloning technology)
1. You are a scientist at a pharmaceutical company in charge of developing drugs against HIV. Discuss four possible targets for drugs that might be effective against this virus.
2. Researchers debate the evolutionary value to the virus of its ability to cause disease. Many argue that viruses accidentally cause disease and only in animals that are not the natural host. They state that this strategy may eventually prove fatal to the virus's future in the host. It is reasoned that the animals will eventually develop immune mechanisms to combat the virus and prevent its spread. Another group of researchers supports the view that disease is a way to enhance the survival of the virus. What rationale would this group use to support its view?
Critical Thinking
1. Would ID50 and LD50 necessarily be the same for a given virus? Why or why not?
2. The observation that viruses can agglutinate red blood cells suggest to some people that both viruses and red blood cells must have multiple binding sites. Is this a good argument? Why or why not?
3. An agricultural scientist is investigating ways to prevent viral infection of plants. Is preventing the specific attachment of the virus to its host cells a possible way to prevent infection? Why or why not?
4. Why is it virtually impossible to stamp out a disease caused by a zoonotic virus?