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Viral Classification/Genome Replication


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What are the three basic replication stategies of viruses?
3.DNA based with reverse transcriptase
Relate (+) and (-) sense RNA to the orientation of mRNA.
(+) sense RNA has the same polarity and orientation as mRNA, (-) sense RNA has the opposite polarity and orientation.
For viruses that employ a DNA-based replication strategy, what polymerases are used for replication and transcription? Are they virally encoded or part of the host cell?
*replication: DNA-dependent DNA pol
*transcription: DNA-dependent RNA pol
*most often the virus uses hist cell enzymes
How are (+) sense ssRNA viruses...
*Replication is via a virally-encoded RNA-dependent RNA pol...a (-) sense template is made first and then (+) sense strands polymerized
*because they are in the same orientation as mRNA these viruses are directly translated by host cell ribosomes without a separate transcription step
How are (-) sense ssRNA viruses...
*a virally encoded RNA-dependent RNA pol is used for replication...this RNA pol is typically packaged inside the virion
*after the viral RNA-dependent RNA pol has synthesized (+) sense RNA, translation occurs via host cell ribosomes
How do dsRNA viruses replicate?
Via a RNA-dependent RNA pol that is packaged inside the virion.
What can be said about the nature of the viral genome and its tendency to gravitate to certain parts of the host cell?
DNA viruses tend to move into the nucleus, while RNA viruses tend to stay in the cytoplasm.
What is the reverse transcriptase enzyme?
A virally encoded RNA-dependent DNA pol that is also able to degrade RNA that is in a hybrid complex with DNA and synthesize DNA in a DNA-dependent manner.
What are the three reactions involved in reverse transcription?
1.Synthesis of DNA alongside viral RNA to form a hybrid complex.
2.Selective degradation of viral RNA
3.Synthesis of a complementary strand of DNA to form a homogenous complex
Net amplification occurs when RT synthesizes a complementary strand of DNA alongside the viral RNA.
False: because the viral RNA strand will be degraded, there is no net amplification in this replication step. Once the DNA complex is complete, it is transcribed in a manner that does amplify the viral genome.
What is the mutation rate for RT? What does this imply?
*1 error per every 10^4 nucleotides
*this means there is a mutation for every genome transcribed, so even within a single patient no two viruses will be exactly the same (theoretically atleast)

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