Control Of Virus Replication - RNA Viruses Flashcards
(35 cards)
What two strategies are used by RNA viruses that need to copy their genome in a host cell that only copies DNA molecules?
- Conversion into DNA, followed by host RNA transcription
- Specific viral replication machinery utilising a viral RNA-dependent RNA polymerase
What must all RNA viruses have in their life cycle to enable protein synthesis?
An mRNA equivalent
In the case of dsRNA, what has to happen for translation to occur?
Genome cannot function as mRNA so requires synthesis of (+)RNA before translation can occur
What happens with translation in the case of (+)ssRNA?
Virus genome acts as mRNA directly
Translation can occur immediately
What happens with transcription/translation in the case of (-)ssRNA?
Transcription required before translation
Transcription either in cytoplasm or nucleus
What happens with ambisense ssRNA?
Z mRNAs produce backwards 5’ to 3’
L ORF is produced in opposite direction
Common hair pin structure in middle of RNA molecule
This acts as a break
Can have genes made in two directions, so one piece of RNA is encoding two proteins in different directions
How do retroviruses undergo transcription?
Use reverse transcriptase to make dsDNA then use cellular polymerase to make mRNA
What do dsRNA viruses use for transcription?
Use a polymerase carried with the virus inside of the virion when it infects
Do RNA or DNA viruses have a higher evolution and mutation rate?
RNA viruses have much higher rate
What is quasi-species a fancy name for?
A population
Why are proteins that RNA viruses make multifunctional?
Because they can’t encode multiple proteins, the genomes are too small
Where do RNA viruses undergo translation and transcription?
In the cytoplasm unlike DNA viruses
What RNA virus needs to go into the nucleus?
Influenza because it needs to initiate translation by snatching mRNAs being made in nucleus and transcribed
What is the advantage of influenza being segmented?
Can make proteins in each areas
What is the consequence of segmented genomes to the host?
If you get infected with two viruses, they can be very different and may pick up one segment from each parent resulting in antigenic shift
What type of genome do paramyxoviruses have?
Negative strand RNA virus
What do + strand copies of a negative genome terminate in different places?
Capsid proteins and viral glycoproteins encoded by genes at one end
Polymerase and helicases encoded by genes at other end
Need less coding potential to make enzymes, whereas to make virus particle, need tens of thousands of capsid proteins
Will there be more structural or non structural proteins in replication cycle?
More structural
What type of genome does hepatitis C virus have?
Linear, ss, (+) RNA genome
What are the 4 receptors used for hepC binding?
CD81, SR-B1, claudin1, occludin
What happens when hepC goes into endosome?
There is a pH change, fuses membrane
What happens when RNA then goes to ER?
Goes to ribosome, get translation and get polyprotein. This is manufactured as a single protein that passes through the ER membrane many times
What are the two models for HCV?
First is virus particle with glycoproteins on the outside, viral RNA in the middle. Attached to LDL and HDL (2 particle model)
Second is hybrid-particle model. Blob of fats with some apo lipo proteins on the outside, then a few copies of glycoproteins sticking out to allow it to dock
What is the HCV entry process?
- HCV lipo-viral particles assocaited with glycoaminoglycans and LDL receptor
- The E2 glycoprotein interacts with cell-surface receptors SR-B1 and CD81
- Interaction with the tight junction proteins claudin 1 and occludin
- Entry into the cytoplasm occurs by pH-dependent fusion of the viral envelope with the endosomal membrane, releasing the viral RNA
