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NBME 22 Answers

nbme22/Block 4/Question#5

A new virus has been isolated that causes ...

Single-stranded positive-sense

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according to medbullets link ns ss RNA must carry RNA dependent RNA polymerase (so that is out).

also, according to medbullets there are very few ds RNA viruses, so "most likely" will be ss. Also, RNA-dependent DNA polymerase = Reverse Transcriptase. Since HIV is a ss ps RNA virus with RT, they've described an HIV cousin. not sure beyond this.

nc1992  negative stranded can't be read by a translator so it needs to be transcribed into + first. Only then can it be used for protein. + is basically mRNA already. There's only one double stranded RNA family as far as I know- Reovirus so no encephalitis +2  




Ok, so RNA dependent DNA polymerase is for reverse transcriptase... single stranded + use RNA dependent RNA polymerase. Can someone explain?

hyoid  The only thing I can think of is that HIV is a (+)-sense single-stranded RNA virus that relies on an RNA dependent DNA polymerase (reverse transcriptase) to synthesize DNA. +  
haliburton  according to [medbullets link](https://step1.medbullets.com/step1-microbiology/104196/rna-viruses_) ns ss RNA must carry RNA dependent RNA polymerase (so that is out). also, according to medbullets there are very few ds RNA viruses, so "most likely" will be ss. Also, RNA-dependent DNA polymerase = Reverse Transcriptase. Since HIV is a ss ps RNA virus with RT, they've described an HIV cousin. not sure beyond this. +  
some0217710  Can’t think of any retroviruses outside of HIV and HTLV and they’re both +ssRNA +  




I think this was referring to reverse transcriptase, and the only two viruses I knew that used them were HepB and HIV/retroviruses. Given the context I picked HIV/retroviruses which are SS + sense. This was kind of weird though since the virus was “new” ... but I’ve learned that “new” usually means very little on these tests.

yotsubato  "New" means made up fantasyland virus +2  
yotsubato  Also Hep B is a ssDNA virus that goes to RNA, then is reverse transcribed to dsDNA +  




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submitted by niboonsh(89),

My guess is that they are referring to Retrovirus (HIV/HTLV)- a single stranded positive sense linear RNA. Retroviruses are known to carry reverse transcriptase (RNA-dependent DNA-polymerase). The encephalitis is what threw me off cuz I automatically thought of the many negative sense RNA viruses that cause encephalitis (like arenavirus or bunyavirus). Apparently there have been a few causes of HTLV causing encephalitis... maybe this is what they were trying to get at? Idk but i just spent way too much time on this damn question https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5878187/





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submitted by meddeku(0),

Japanese encephalitis virus according to Dr. Google (ncbi)

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