Ch1 Understanding HIV Complete Question Guide With Accurate Answers.
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AZT
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AZT
When did HIV enter the human population? - correct answer HIV entered the population several times, from SIV strains found in several primates.The SIV strain that moved from chimpanzee to the first human host probably existed between 1915 and 1941, with...
When did HIV enter the human population? - correct answer HIV entered the
population several times, from SIV strains found in several primates.The SIV strain that moved from
chimpanzee to the first human host probably existed between 1915 and 1941, with 95% confidence.
How is the age of the last common ancestor of HIV calculated? - correct answer
Estimated by calculating how quickly the group M strains diverged from each other throughout the
1980s and 1990s, and assuming rate is constant, back-calculating to estimate the year when they all
diverged from their last common ancestor- when moved from chimp to human.
From what source did HIV-1 enter the human population? - correct answer
Based on genetic sequences it is clear that it is derived from a form of SIV found in chimpanzees.
How many times has HIV-1 been introduced to the human population? - correct answer
At least 3.
From what source did HIV-2 enter the human population? - correct answer
Based on genetic sequences, from a form of SIV found in sooty mangabeys.
How many times has HIV-2 been introduced to the human population? - correct answer
At least 2.
How does the HIV population in a human host evolve resistance to the drug AZT? - correct answer
HIV has a very high mutation rate, a rapid reproductive rate, and an enormous population size. This
means that at any given time, a human infected with HIV is carrying tens of millions of HIV virions with
millions of different random mutations. Inevitably, sooner or later, a mutation will occur that confers
resistance to AZT.
What type of mutation causes the human host to have resistance to the drug AZT? - correct answer
Typically a mutation that causes greater selectivity in the active site of the reverse transcriptase enzyme.
, What is the evolutionary process in which AZT becomes essentially not effective? - correct answer
Patient begins taking AZT. This prevents or slows replication of most HIV virions, and those strains die
out. But the lucky virion with the right mutation will survive and will be able to replicate. There is
differential reproductive success that is linked with a heritable trait.The surviving HIV virions then
repopulate the host. Soon the entire HIV population is composed of resistant virions. Formerly, there
was only 1 resistant virion among millions; now all of the millions are resistant. The population has
evolved.
How might the AZT scenario explain the evolution of antibiotic resistance in a population of bacteria? -
correct answer The process is identical.. The only difference will be in the
specific nature of the mutation. It will not be occur in the gene for reverse transcriptase, but in some
bacterial gene.
In the early 1990s, researchers began to find AZT-resistant strains of HIV-1 in recently infected patients
who had never received AZT. How can this be? - correct answer These patients
had been infected by other patients who had HIV and were receiving AZT treatment for it, and yet
continued to engage in activities by which resistant strains of HIV "escape" to the general population.
What traits of HIV contribute to its rapid evolution? - correct answer It can
generate the key "lucky" mutations extremely quickly. This is because HIV has a very high mutation rate,
an extremely fast reproductive rate, and a very large population size (within one host).
Given the risk of evolution of resistance, why do you think the two patients from the earlier scenario
were not given high doses of AZT immediately? - correct answer Because of
the serious side effects of antiviral drugs. Since viruses use their host cell's molecular machinery, any
drug that can stop viral replication usually interferes with normal healthy cells as well. AZT can disrupt
cell division because it interferes with DNA transcription in healthy cells, not just in HIV-infected cells.
What is the idea behind multiple-drug therapy for HIV? - correct answer To
increase the number of mutations required for resistance and therefore reduce the amount of genetic
variation in the viral population for survival in the presence of drugs.
Could we achieve the same effect as multiple-drug therapy by using antiretroviral drugs in sequence
instead of simultaneously? Why or why not? - correct answer No. Likely would
lead to resistance to all the drugs. This is because the HIV population would only have to develop
resistance for one drug at a time, which is quite easy for it to do. The key to multiple drug therapy is that
the drugs are given simultaneously, so that an HIV virion must have four or five simultaneous mutations
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