The enormous genetic diversity of HIV has made it especially difficult to create a vaccine against the virus. We can attribute this genetic diversity to

Question

A.  mutation hotspots in the hemagglutinin (H) molecule.
B.  mutation hotspots in the CD4+ molecule.
C.  the high error rate of reverse transcriptase.
D.  the high sensitivity of the virus to UV radiation.

Clarify Question
· What is the key concept addressed by the question?
· What type of thinking is required?
 
Gather Content
· What do you already know about HIV infection?
 
Choose Answer
· Given what you now know, what information and/or problem solving approach is most likely to produce the correct answer?

Reflect on Process
· Did your problem-solving process lead you to the correct answer? If not, where did the process break down or lead you astray? How can you revise your approach to produce a more desirable result?

Answer 1

C.  the high error rate of reverse transcriptase.

Clarify Question
· What is the key concept addressed by the question?
        o This question addresses HIV infection.
· What type of thinking is required?
        o This question is asking you to weigh and judge evidence, or evaluate, to choose the best of the possible answers.
 
Gather Content
· What do you already know about HIV infection?
        o HIV is a retrovirus, so the RNA genome is copied into DNA, then back into RNA again.
        o Inside the host cell, the HIV particle sheds its protective coat.  Reverse transcriptase synthesizes a double strand of DNA complementary to the virus RNA, often making mistakes and introducing new mutations.
        o This double-stranded DNA then enters the nucleus  and is incorporated into the host cell’s DNA. After a period of dormancy the HIV provirus directs the host cell’s machinery to produce many copies of the virus.
 
Choose Answer
· Given what you now know, what information and/or problem solving approach is most likely to produce the correct answer?
        o Does HIV acquire mutations due to mutation hotspots in the hemagglutinin (H) molecule? No, that is a feature of influenza virus, not HIV.
        o Does HIV acquire mutations due to mutation hotspots in the CD4+ molecule? No, the CD4+ molecule is part of the human cells, not the HIV virus.
        o Does HIV acquire mutations due to the high sensitivity of the virus to UV radiation? No, this is not a feature of HIV.
        o Does HIV acquire mutations due to the high error rate of reverse transcriptase? Yes! This is the best explanation. As a retrovirus, the HIV genome is copied by reverse transcriptase, which has a high error rate.
 
Reflect on Process
· Did your problem-solving process lead you to the correct answer? If not, where did the process break down or lead you astray? How can you revise your approach to produce a more desirable result?
        o The question required you to weigh and judge evidence, or evaluate, to choose the best of the possible answers.
        o Did you recognize that HIV is a retrovirus, and thus relies on reverse transcriptase to copy its genome from RNA to DNA?