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Virology Exam 2: Study Questions with Correct Answers
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Virology Exam 2: Study Questions with Correct Answers
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Virology Exam 2: Study Questions with CorrectAnswers
Why must (-) strand viral RNA be coats with protein in the virion? Why
not (+) strand viral genomes? Are there exceptions for the latter? Correct
Answer-(-) 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? Correct
Answer-Yes because host doesn't make RdRp.
For viruses with (-) sense RNA genomes, the (+) strands and mRNA are
the same. True or false? Why? Correct Answer-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?
Correct Answer-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? Correct Answer-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? Correct Answer-
(-)RNA is not infectious as no RdRp is present. But (+)RNA is
infectious (will be translated to make proteins)
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