Virology IV Flashcards
Most DNA viruses contain dsDNA. What is an exception?
Parvovirus B19; adeno-associated virus (may be less important).
What is an example of an RNA virus with dsRNA?
rotavirus
What is a capsid? What are two kinds of capsids?
a capsid is a protective protein shell around a virus. usually made from repeating protein subunits. may be either helical or icosahedral. icosahedral capids are usually made of more than 1 protein
What is a viral envelope? What does it contain? What kinds of viruses have envelopes?
envelopes are made from cell membranes. contain a lipid bilayer interspersed with viral glycoproteins or other membrane proteins. Enveloped viruses tend to be less stable- usually NOT fecal/oral viruses (usually seen in direct contact viruses (blood, sex, insect/animal bite).
ourter surface proteins determine type-specificity.
What are the 4 stages of viral growth?
- adsorption
- eclipse (viral uncoating- 2-12 hrs). no infectious virus can be detected.
- synthetic phase: new virus particles are assembled- 12 hrs post infection
- latent: no extracellular viruses
eventually viruses will be detectable extracellularly. plateau level of viruses is eventually reached.
What is the difference between a receptor and a co-receptor?
time. typically, a virus will bind a receptor first (usually further from the plasma membrane), which causes a conformational change in the virus that makes it able to bind its co-receptor
In what two ways do viruses enter cells?
receptor-mediated endocytosis
direct membrane fusion
what happens during receptor-mediated endocytosis?
- ligand binds receptor
- membrane invagination with clathrin on the cytosolic side.
- pit pinches off
- vesicle fuses with early endosome
- early endosomes transported to late endosomes, which are acidic- ligands and receptors disossiate
- late endosomes fuse with lysosomes: most viruses escape before this stage (reoviruses are the only exception)
example of pH-dependent membrane fusion
hemagglutinin-neuraminidase protein of influenza virus
what happens during virus uncoating of the influenza virus?
M2 protein undergoes a conformational change at the low pH inside the endosome. this leads to activation of ion channel activity. protons enter the virus. interactions between the viral ribonucleoprotein (RNP) and the envelope protein M1 are disrupted. leads to virion disassembly.
What are some features of DNA viruses? exceptions? (ie. what do they bring with them and why)
tend to encode their own DNA polymerases
exceptions are parvoviruses and papillomaviruses (HPVs and parvovirus B19)
viruses without DNA pol must use cellular DNA pol- can only replicate in actively dividing cells.
What are the two groups of dsDNA viruses? what are some examples?
2 groups- those that replicate in the nucleus and those that replicate in the cytosol
cytomplasm example: poxviruses. need to encode factors to ensure transcription and replication of their genomes.
what is an example of a viruse with ssDNA genome? where does replication occur? what are the two classes of genes?
parvovirus
replication occurs in the nucleus
early genes are transcribed before DNA replication begins and products play a role in genome replication
late genes are transcribed after genome replication has started to form structural components of the virus
What is one important feature of dsRNA viral genomes? An example?
they tend to be segmented- each segment transcribed separately to produce individual monocistronic mRNAs (rotavirus)
What are the 2 groups of ss (+) RNA viruses? An example in each group?
- viruses with polycistronic mRNA. they produce polyprotein that must be proteolytically processed. example is the flaviviruses (west nile, dengue, etc.)
- complex transcription- 2 rounds of translation or subgenomic RNAs needed to make genomic RNA. Ex: rubella.
