Download Chapter 19 Homework Exposure to the HIV virus doesn`t necessarily

Chapter 19 Homework
Exposure to the HIV virus doesn’t necessarily mean that a person will develop AIDS. Some people have
genetic resistance to infection by HIV. Dr. Stephen O’Brien from the U.S. National Cancer Institute have
recently identified a mutant form of a gene, called CCR5, which can protect against HIV infection. The
mutation probably originated in Europe among survivors of the bubonic plague. The mutated gene
prevents the plague bacteria from attaching to cell membranes and, therefore, from entering and
infecting body cells.
Although the HIV virus is very different from the bacterium that causes the plague, both diseases affect
the exact same cells and use the same method of infection. The presence of the mutated gene in
descendants of plague survivors helps prevent them from contracting AIDS. Pharmaceutical companies
are using this information as the basis for a new approach to AIDS prevention. This would be very
important in areas of the world where the mutation is scarce or absent, such as Africa.
1. The most likely method by which the mutated CCR5 gene prevents AIDS is by
a. Blocking the protein channels that allow the virus to enter the cell
b. Directing the formation of lytic enzymes packaged in the lysosomes.
c. Being presented on immune system cells to target the virus from attack and destruction.
d. Coding for a mutant receptor protein on the cell membrane, this not allowing the entry
of the virus.
2. Which of the following shows the steps of a retroviral infection in the proper order?
a. Virus locates host cells  enters nucleus  alters host cell DNA  destroys cell
membrane.
b. Virus locates host cells  alters host cell DNA  host cell produces copies of virus 
copies enter host cell nucleus  nucleus leaves cell.
c. Virus locates host cells  penetrates cell membrane  enters nucleus  alters host
cell DNA  host cell produces copies of virus.
d. Virus locates host cells  penetrates cell membrane  viral RNA used to make DNA 
host cell produces copies of virus.
3. Lateral gene transfer involves the movement of genes between members of a species without
sexual reproduction. In bacteria, there are three mechanisms for this: conjugation,
transformation, and transduction. Predict how these processes are most likely to affect bacteria.
a. Their DNA content will be reduced.
b. The amount of RNA in the cytoplasm will be increased.
c. Their genetic diversity will be increased.
d. Their metabolic needs will be modified to give a selective advantage.
4. What characteristics of a living organism are absent in a virus?
5. What are the structural components of a virus?