Viral Genomes
What does viral genetic material encode for?
Structural proteins of the capsid and viral proteins essential for initiation of virus replication.
What are arboviruses and in what classification scheme are they relevant?
Arthropod-borne viruses, disease-based classification
What is the function of the capsid?
To provide a protein shell where the chemically liable viral genome can be maintained in a stable environment.
What did the ICTV develop?
A single, universal taxonomic scheme for all viruses infecting animals, plants, fungi, bacteria, and archaea.
What are the components of the virion (virus particle)?
The genome, capsid, and envelope (when present).
In the basics of viral classification, what questions can be asked about the genome in the capsid?
DNA or RNA, single or double-stranded, circular or linear, composed of a single piece or segmented?
How is a virosphere view generated?
Combining the Baltimore basis along with the nature of the host and detailed genetic characterization of critical viral proteins.
What is notable about the capsids of the poxvirus?
They are distinguished by having a number of different shapes characterizing specific members of the group.
What would be the expected morphology of a virus in the parvoviridae family?
Isometric
The exterior of virions contains proteins that interact with specific proteins on a surface of a cell - what stage of viral replication does this best apply to?
Stage 1, interaction with the host cell and introduction of the viral genome
Why is there a great rate of genetic change in viruses?
Due to the rapidity and frequency of genome replication and the associated opportunity for error.
Name one 'drawback' in the Baltimore scheme of virus classification.
What technique can be used to study the capsid structure of smaller icosahedral viruses and why can it not always be applied to larger viruses?
X-ray crystallography, the method requires the ability to crystallize the subject material
What six viral features does the ICTV use to classify a virus?
Nature of the genome, Presence of an envelope, Morphology, Genome Configuration, Genome Size, and Host Type
Are envelopes a feature of all viruses? If not, what specific viruses are they a defining feature of?
No, however, they are an important defining property of different groups of animal viruses.
What is the difference between positive-sense RNA viruses and negative-sense RNA viruses?
Positive-sense: Genome is in the same sense as mRNA
Negative-sense: Genome is in the opposite (complementary) sense of mRNA
What is the Baltimore scheme based on and what is the logic behind that consideration?
Based on the way a virus produces mRNA during infection, the logic being that to replicate all viruses must express mRNA for translation into a protein.
Why is the shape of a virus determined by a capsid and not on whether or not the virus is enveloped?
What is a notable achievement of the ICTV?
The recognition of a limited number of viral features that can be used for classification.
What makes up a viral envelope?
A lipid bilayer derived from the cell in which the virus replicated and from virus-encoded membrane-associated proteins.
What is required in the replication of RNA viruses and what does the host cell lack that makes this necessary?
The expression of specific enzymes not present in the uninfected host cell, because the cell does not have the machinery for RNA-directed RNA replication.
Define the polythetic nature of virus groupings and explain why this applies to the members of virus families.
No single property can be used as a defining property on the basis that it is universally present in all members of a group and absent in the members of another. This is due to the inherent variability of the members in virus groupings.
What are the two regular shapes of viruses and how do they come about?
1. Helix: Capsomers associate with helical nucleic acid as a nucleoprotein
2. Icosahedron: Capsomers form a regular solid structure enfolding the viral genome
Why is the 2017 ICTV report not considered complete?
The pace of discovery of viruses and characterization of the genes they encode for ensures that the number will change.
What three major roles do good classification schemes have in organizing the plethora of entities virologists study?
1. Organizing the growing flood of genetic and molecular information
2. Provides a framework for understanding ways viruses can utilize cellular genes to maintain themselves
3. Provide guides to the origins of virus groups and the relationships between them