USMLE Forums banner
1 - 10 of 10 Posts

·
Registered
Joined
·
116 Posts
Discussion Starter · #1 ·
Five different viruses are added to cultures of permissive cells treated with Actinomycin D, a drug which binds to DNA and inhibits mammalian and viral DNA replication and transcription by all mammalian nuclear RNA polymerases. Which virus should you expect to produce infectious progeny?

A. Herpes simplex virus, Type I.
B. Human immunodeficiency virus - 1.
C. Human polyoma virus.
D. Influenza virus.
E. Yellow Fever virus.
 

·
Registered
Joined
·
71 Posts
B

B

I'm not good at explaining why I choose a certain answer, but I will say that I know there are is no cure for HIV, so actinoymycin D should have no effect on it...i think...
 

·
Registered
Joined
·
487 Posts
Let me simplify this...

A. Herpes simplex virus, Type I. --- dsDNA virus
B. Human immunodeficiency virus - 1. ---- RNA virus (rep:RNA-dependent DNA polymerase)
C. Human polyoma virus. --- dsDNA virus
D. Influenza virus. --- RNA virus (rep:RNA-dependent RNA polymerase )
E. Yellow Fever virus --- RNA virus

Now I need to know what are the ongogenic viruses. HIV is the only one on the list can cause cancer and others don't. So, I'll go with Chioce B) HIV :confused:
 

·
Registered
Joined
·
590 Posts
D. Influenza

I would choose D. Influenza because it is the only negative-sense RNA on the list. It brings its own RNA-dependent RNA polymerase, so it shouldn't be affected.

@aktorque: why oncogenic?

FA 2011/2010 p. 169/170 SS- viruses:
Bring A Polymerase Or Fail Replication
(Bunyavirus, Arenavirus, Paramyxovirus, Orthomyxovirus, Filovirus, Rhabdovirus)
 

·
Registered
Joined
·
116 Posts
Discussion Starter · #7 ·
The answer is E.

This Q is simply asking about a very high yield concept. Which one is +ve RNA virus?

Actinomycin D acts in the nucleus. So every thing in the nucleus, whether mammalian or viral is shut off, as the Q stem is clearly saying.

+ RNA is exactly the same as mRNA. It can be translated directly in the cytoplasm by ribosomes. One of the translated proteins is a Polymerase that first transcribes it into -ve strand, then transcribes that -ve stand into +ve stands for more progeny.

For those who answered B, We are not talking about whether AIDS is curable or not. It goes on in experimental culture cells. Besides, HIV virus makes a double stranded DNA that integrates into host DNA and uses his machinery.

@Mondoshawan, I also chose D. What was in my mind that Most RNA viruses replicate in the cytoplasm and -ve RNA virus have their own polymerase, but their are exceptions. Their are only two RNA viruses that replicate in the nucleus, ortho (influenza) and retro. This is what makes D wrong.

Here are two more Qs that test the same concept.

A virus is isolated in the laboratory. Electron microscopy shows that new virions assemble in the cytosol and are released by cell lysis. Virions lack envelopes and are approximately the size of Hepatitis A virions. The genome is single-stranded and replicates in the cytoplasm; no dependence on nuclear functions can be demonstrated. When genomes purified from virions are added to cultured cells, a small amount of progeny virus is produced. Based on these data, what is the most likely nature of the viral genome?

A. DNA of (+) polarity.
B. DNA of (-) polarity.
C. RNA of (+) polarity.
D. RNA of (-) polarity.

A patient develops diarrhea produced by a previously-unknown virus. Electron microscopy shows that the virus replicates in the cytoplasm and lacks an envelope. Virions are small, approximately the size of Polio virions, and contain single-stranded genomes. When nucleic acid purified from virions is added to cultured cells, a small amount of progeny virus is produced. Based on these data, what is the most likely nature of the viral genome?

A. Single-stranded DNA of (+) polarity.
B. Single-stranded DNA of (-) polarity.
C. Single-stranded RNA of (+) polarity.
D. Single-stranded RNA of (-) polarity.

Font Parallel Diagram Circle Rectangle
click image to enlarge
 

·
Registered
Joined
·
487 Posts
@aktorque: why oncogenic?
I was thinking that some viruses carry oncogenic properties with them, and when they infect human host cell they able to integrate their DNA molecule into host cell DNA causing cancer (eg: Hep B virus).

I was thinking that HIV causing Kaposi's sarcoma, but it actually causes by HHV8. Anyway my ans is wrong. We all forget to see (+)/(-) sense of the RNAs here.
 
1 - 10 of 10 Posts
Top