02/27b Viral Genetics and Host Interactions Flashcards
What type of genome do herpes viruses and adenoviruses have?
Double-stranded DNA
What type of genome does influenza virus have
Single-stranded (-) RNA
What type of genome do polio and hepatitis C have?
Single-stranded (+) RNA
Why is the poliovirus life cycle so simple?
It has a (+) strand RNA genome, which means its genome is essentially a strand of mRNA
Once the viral genome enters the cytoplasm, it does not need to undergo any processing to being protein synthesis
What two types of proteins are synthesized by poliovirus?
1) Polymerase that is capable of synthesizing a (-) strand from the (+) strand, to be used as a replicative template
2) Structural proteins to assemble the capsid
Do (+) strand RNA viruses ever enter the nucleus?
NO
What are the six most important features of (+) strand RNA virus biology?
1) Viral polymerase has an extremely high error rate because it has no access to any repair mechanisms
2) Very compact genome, to avoid creating so many errors that they can no longer produce viable progeny
3) Monocistronic genome that is expressed in one piece and subsequently processed into distinct proteins
4) NO complex regulation of gene expression, due to monocistronic genome (all or nothing)
5) Viral genetic material cannot persist inside the cell (no latent mode)
6) High degree of genetic variability, which affects treatment and vaccine prospects
What must a (-) strand virus do after entering a host cell, before it can even begin replicating?
(-) strand RNA must enter the nucleus and use its own proteins to synthesize a (+) strand mRNA copy, as well as a (+) strand RNA replication template (NOT mRNA)
What are the seven most important features of (-) strand RNA virus biology?
1) Viral polymerase has an extremely high error rate because it has not access to any repair mechanisms, just like (-) strand RNA viruses
2) Very compact genome, to avoid mistakes
3) Monocistronic genome that is post-processed into polyproteins
4) Often have segmented genomes
5) Some regulation of gene expression that occurs in the nucleus
6) Viral genetic material cannot persist inside the cell
7) High degree of genetic variability
Why is a dsDNA viral genome “safe” in the nucleus? Why does this mean for the persistence of a dsDNA virus infection?
The host cell has no way of distinguishing the viral genome from its own genome
This means that a dsDNA virus can persist for long periods of time inside host cells
What are the six most important features of dsDNA virus biology?
1) Faithful genome replication via the host’s replication machinery, including error-correction mechanisms
2) Large genome is possible due to faithful replication
3) Complex regulation of gene expression - has space in its genome to express regulatory elements
4) Viral genome can persist indefinitely in the host cell nucleus, by insertion into the host genome or as an episome
5) Lifelong persistence
6) Latency
What is latency? What types of viruses exhibit it?
The ability of a virus to go completely “silent” (no replication), and then reactivate later and begin replicating and destroying cells
Latency is seen ONLY with retroviruses and dsDNA viruses
What is an acute viral infection? What viruses undergo acute infection?
Viral infection where the virus (and clinical symptoms) are eventually completely cleared
There is NO persistence of viral material or chronic infection
Typical of (+) strand RNA viruses (polio)
What is a chronic viral infection? What viruses undergo chronic infection?
Viral infection that entails constant virus replication and constant evolution and adaptation
Genomic material is NOT permanently maintained
Happens in Hepatitis C infection, but is ATYPICAL of (+) strand RNA viruses
Depends on which organ is infected - HCV could not undergo chronic infection in the brain or other irreplaceable organ
How does a virus initiate latency?
Viral genome is either inserted into the host genome or exists episomally
Latent viruses are able to avoid and counteract the immune system
