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VIROLOGY EXAM 2 STUDY QUESTIONS
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VIROLOGY EXAM 2 STUDY QUESTIONS
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VIROLOGY EXAM 2 STUDY QUESTIONSWhy must (-) strand viral RNA be coats with protein in the virion? Why not (+) strand
viral genomes? Are there exceptions for the latter? - Answers -(-) RNAs are coated with
proteins to allow mRNA synthesis upon entry (with packaged RdRp), as the RNA is not
infectious.
(+) RNAs are not coated because they are translated upon entry.
Exceptions:
(1) retroviral RNA is (+) strand but is coated and has reverse transcriptase to turn back
into DNA.
(2) Coronavirus is (+) strand but is coated because it's very long.
Do all RNA viruses encode their own replication system? Why? - Answers -Yes
because host doesn't make RdRp.
For viruses with (-) sense RNA genomes, the (+) strands and mRNA are the same. True
or false? Why? - Answers -False: sometimes the mRNA is shorter than the (+) strand,
but the full (+) strand is needed as a template for the (-) RNA
(1) Influenza: the mRNA is ~20 BPs shorter than the (+) mRNA
(2) VSV: Maybe the same?
What is the primer for picornavirus replication? The primer for synthesis of influenza
mRNAs? Is all viral RNA synthesis primer-dependent? - Answers -Primer for picorna
(polio) = Vpg-pUpU
Primer for influenza: host mRNA that RdRp must use
Not all viral RNA synthesis is primer-dependent! (Examples: alphavirsues = (+) RNA,
VSV = (-) RNA, and reovirus/rotavirus = dsRNA
Know the flow of information for (+), (-) and ds RNA genomes. Which genomes are
accompanied by an RdRp in the virus particle? How are proteins encoded in viral RNA
genomes? - Answers -Know the Baltimore scheme here!
(-) ssRNA and dsRNA need RdRp in virus particle.
Proteins may be encoded as polyproteins, or by subgeneric mRNAs.
When the genome of a (-)ssRNA virus is purified and introduced into cells that are
permissive for the original virus, does replication occur? (i.e., is it infectious)? Why? If
you did this same experiment with a (+) sense ssRNA virus, would viral replication
ensue? - Answers -(-)RNA is not infectious as no RdRp is present. But (+)RNA is
infectious (will be translated to make proteins)
, How is poly (A) added to mRNAs of RNA viruses? - Answers -1. Sometimes it's in the
original template (if lots of Us)
2. Can have untemplated slippage by RdRp at sequence of U's in VSV and influenza
What is the first biosynthetic event that must take place after viral ssDNA enters the cell,
and why? Where does it take place? What about dsDNA? What about gapped dsDNA?
- Answers -The first BIOSYNTHETIC event for all is transcription (AFTER they are
repaired to dsDNA - this is the only template for transcription).
Transcription is first because AT LEAST ONE PROTEIN IS NEEDED FOR VIRAL DNA
SYNTHESIS
Transcription takes place in nucleus, except for poxviruses (in cytoplasm) that encode
their own RNA Pol II
Describe the individual steps that take place during the production and processing of
mRNAs (from DNA) - Answers -Transcription, Capping, PolyAdenylation, Splicing,
mRNA Export
1. RNA Pol II transcribes, beginning at promoter (TATA binds TFIID protein), to create
pre-mRNA
2. We have co-transcriptional capping at 5' end (5'-5' linkage to G)
3. Then, we have post-transcriptional endonucleolytic cleavage and polyadenylation by
host (?) enzymes
4. Finally, we have splicing, which marks mRNA with proteins that deem it ready for
nuclear export
5. mRNA Export.
How is RNA Pol II recruited to the DNA template, and how is transcription regulated?
How do viral proteins regulate transcription? - Answers -Promoter sequences recruit
transcription proteins (E.g., TFIID binds to TATA box). These proteins then ind RNA Pol
II.
Transcription is regulated by:
1. DNA binding proteins (that bind to silencers/enhancers) or co-activators (which affect
how tightly DNA is wound around chromatin)
Viral proteins can bind promoter control sequences, OR act as co-activators (so they
can affect either of the two triggers above).
What is the purpose of splicing? Provide an example? - Answers -3 purposes:
1. Alternate splicing creates more than 1 mRNA / protein from 1 pre-mRNA, so small
genome contains more information (Example: adenovirus alternative splicing give rise to
different proteins)
2. Allow for regulation of production of different proteins
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