Section Bank B/B #19

[NY_Med]

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A vDNA sequence encoding a protein is inserted into a host genome by IN. The protein is translated from the hypothetical mRNA sequence shown.

5

–GGCAACUGACUA–3

Based on the passage, the segment of the original viral genome that encoded this protein had what nucleotide sequence?

1. 5
   
   –GGCAACUGACUA–3
   
2. 5
   
   –TAGTCAGTTGCC–3
   
3. 5
   
   –CCGTTGACTGAT–3
   
4. 5
   
   –UAGUCAGUUGCC–3
   

I understand that HIV is a retrovirus and therefore should start with positive sense RNA, and had an "Oh geez" moment after that question. But doesn't the fact that it says "vDNA" flaw the question conceptually? I saw it did not say "viral genome" or "vRNA" so was like oh okay, they must be looking for the theoretical DNA template. Is it common knowledge (that I missed) to use the term vDNA to term for the whole genome?

 

[Instance_Variable]

HIV is a positive-sense RNA virus as you said. The question states that a vDNA transcript is inserted into the host genome. However, the question isn’t asking about the vDNA transcript, it’s asking about the original positive-sense RNA that is encapsulated in the virus. I feel like the stuff about vDNA is just irrelevant information to throw you off. vDNA is simply the complementary DNA to the original viral RNA genome. I think that’s where you got thrown off.

The way I answered this was that I realized that for a positive sense RNA virus, viral RNA -> vDNA -> mRNA -> viral protein. So, you would need to go backwards from the transcript they gave you to vDNA and then to viral RNA. Since you’re switching the direction of the strand twice, and the answer is RNA, you’ll end up with the same sequence.


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[JimKimSlim]

I can see your train of thought that led to your question. The question mentions vDNA as in the DNA segment was transfected into the host genome. It never implies that the virus is a DNA virus.

When I first looked at this question, I didn't even think of the possibility of looking at the problem from your angle until you mentioned it. Like instance_variable said, just try to first write down in sequence carefully. You should know HIV is positive-sense a RNA virus, and process of elimination can lead to the right answer.