Nature of Virions
Terms
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- What are viroids and where can they be found?
- They are essentially small, transmissable RNA plasmids found in plant cell nuclei.
- What is segmentation?
- When some viral RNA genomes exist as multiple non-identical molecules per virion.
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T/F:
Enveloped viruses code for enzymes that synthesize their lipid coats. - False: the lipid envelope is derived from the host membrane.
- What are the three general categories of nucleocapsid morphology?
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1.Helical (rod-shaped)
2.Icosahedral (spherical)
3.Complex - What are two functions of the capsid?
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1.Condense and confine viral genome
2.Confine other molecules (e.g. enzymes) to be co-packaged with the genome
3.Isolate the genome from damaging molecules (e.g. nucleases) -
T/F:
The capsid is not hermetically sealed and as such small molecules are able to enter. - This is true and the basis for entry of certain antiviral drugs.
- What determines the flexibility of helical nucleocapsids?
- The strength of the protein-protein interactions in the nucleocapsid.
- How many faces and how many vertices does an icosahedron have?
- 20 faces and 12 vertices.
- How do viral proteins end up inserted into a lipid envelope?
- The viral proteins are synthesized inside the cell and then move to the plasma membrane, where they accrue in small patches. The cytoplasmic domains of these proteins interact with the nucleocapsid and allow it to dock. The virus then pushes out in an exocytotic fashion.
- Does a lipid envelope increase or decrease the stability of the nucleocapsid?
- It actually decreases the stability of the virus and does not survive well in the presence of acids, bases, or lipid solvents. They are not stable in a dry, non-aqueous environment either.
- How do lipid envelopes affect the flexibility and rigidity of viruses?
- They are more flexible and less rigid than non-enveloped nucleocapsids and thus exhibit a greater degree of pleomorphism.