Question on viruses

[nm825]

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1) What exactly do viral nucleic acids code for? Is it just the capsid proteins?

2) Am I correct in assuming plus strand RNA doesn't need to enter the nucleus and translation occurs on the ribosomes in the cytoplasim, while DNA and negative strand viruses must first enter the nucleus of the host cell to get to the RNA polymerase for transcription, then translation proceeds as normal in the cytosol?

 

[orderofthescar]

1) What exactly do viral nucleic acids code for? Is it just the capsid proteins?

2) Am I correct in assuming plus strand RNA doesn't need to enter the nucleus and translation occurs on the ribosomes in the cytoplasim, while DNA and negative strand viruses must first enter the nucleus of the host cell to get to the RNA polymerase for transcription, then translation proceeds as normal in the cytosol?

1) They do encode capsid proteins. Their genome can also encode their own replication machinery and enzymes that interfere with the host cellular processes.

2) You are correct in assuming the +RNA acts as the mRNA and doesn't enter the nucleus, and the DNA viruses enter the nucleus to use the RNA polymerase.

The -RNA viruses don't need to enter the nucleus. Negative strand viruses are transcribed into positive strand in the cytoplasm using their own packaged polymerase, and this positive strand is then translated into protein. They can't use the RNA polymerase in the nucleus because that polymerase is DNA-dependent (it only transcribes DNA to RNA - negative strand RNA viruses need to transcribe RNA to RNA).

There are exceptions -- for example, influenza virus is a negative strand RNA virus that enters the nucleus. There are also funky retroviruses that are RNA but integrate into the genome (thus they enter the nucleus). There are also DNA viruses that replicate in the cytoplasm. I highly doubt the MCAT would touch on those 🙂 hope this helps