Hello, I was wondering if any other tests take a similar format to the test I've attached a sample of , I'm aware of the MCAT and the ACT Science but both a still pretty different.
I'd really appreciate any insight :-D
Passage 3
Once a virus has entered a cell, it cannot begin making copies of itself immediately. Only a subset of viruses contains all of the enzymes necessary for transcribing their own genome, and none can make the ribosomes and tRNAs necessary for translating mRNAs. For a particle to make more particles, it must exploit the host cell's biosynthetic machinery. How does this process begin? The answer depends on the nature of the virus's genome.
HIV (Human Immunity Virus) is a retrovirus. Two copies of the RNA genome and about 50 molecules of reverse transcriptase lie inside the core of each particle. Soon after these molecules enter a host cell, reverse transcriptase makes cDNA versions of the viral genome, using nucleotides and ATP from the cell. A viral protein called integrase then catalyzes the cutting of host DNA, the insertion of the viral genome into the host DNA sequence, and the reannealing of the DNA strand. A copy of the HIV genome is now integrated into the host chromosome.
When biomedical researchers first began the search for a drug capable of stopping HIV infections, they focused on disrupting this part of the infection cycle. Specifically, they set out to find molecules that would obstruct reverse transcriptase and prevent HIV's genome from being copied.
The first widely prescribed anti-AIDS drug was a molecule called azidothymidine (AZT) This molecule is so similar in structure to the nucleotide thymidine that it is recognized by reverse transcriptase. When the virus's genome codes for a thymidine to be placed in a growing strand of cDNA, reverse transcriptase sometimes incorporates an AZT molecule instead. This terminates synthesis because AZT will not accept the addition of another deoxyribonucleotide. In this way, AZT blocks viral replication.
AZT was extremely effective againstthe replication of HIV in the laboratory. Early tests with HIV-infected cell cultures, and later trials with AIDS patients, showed that the drug slowed the rate of infection dramatically.
Not long after AZT was put into widespread use, however, most patients stopped responding to treatment. Why? Is it possible thát HIV evolved resistance to the drug? Researchers tested this hypothesis by isolating HIV strains from patients who no longer responded to AZT. As feared, these strains were resistant to AZT in culture. When the biologists sequenced the reverse transcriptase gene from these HIV strains, they found a smoking gun. In many strains, an identical series of mutations had occurred in the part of the enzyme that binds thymidine. Because the mutations are correlated with resistance to AZT, the most logical conclusion was that these mutations made the enzyme less likely to be fooled by the drug. This is why the mutant HIV strains could complete their replication cycle, even when AZT was present.
This sequence of events should sound eerily familiar. As natural selection has recently favored strains of Mycobacterium tuberculosis that are resistant to the drug called rifampin, and these strains are currently responsible for the resurgence of tuberculosis in the industrial world. A parallel sequence of events has occurred with HIV.
12-The mutant strains of HIV that are resistant to AZT have a reverse transcriptase enzyme that is able to
A) include thymidine instead of azidothymidine in the virus genome
B) differentiate thymidine from azidothymidine.
A
C) bind other nucleotides in the thymidine binding site of the enzyme
D) destroy azidothymidine and makes it unable to bind to the enzyme +
13-Which host cell structures and/or chemicals are used by the HIV virus to include its genome in the host's cell genome?
A) The cell's ribosome's and tRNAs
B) The virus genome and reverse transcriptase enzyme.
C) cDNA and integrase enzyme.
D) Nucleotides and Adenosine triphosphate.
14-The anti-AIDS drug AZT can stop HIV infections by
A) preventing the inclusion of the viral genome into the host's cell genome
B) preventing the addition of the nucleotide thymidine to the growing cDNA strand
C) replacing the thymidine in the structure of the host cell genome.
D) preventing the inclusion of more nucleotides to the growing cDNA strand
15-The HIV virus genome includes
A) two copies of the RNA and reverse transcriptase.
B) RNA, reverse transcriptase and integrase.
C) two copies of the RNA molecule.
D) two copies of the RNA and their cDNA
16- Which of the following is correct about HIV virus?
A) It has the protein needed to include its genome into the host cell's genome.
B) It has all the chemicals needed to reverse transcribe its genome.
C) It can translate its mRNA without need for the host's cell.
D) It uses reverse transcriptase and integrase to make copies of its genome.
17-The evolution of HIV that is resistant to AZT is another recent example of
A) artificial section
B) natural selection
C) convergent evolution
D) coevolution
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