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24 Cards in this Set
- Front
- Back
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Viruses w segmented genomes can... |
rearrange/swap their genome segments |
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Transfection |
Process by which VIRAL DNA gets into a cell |
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Transformation |
Process by which ANY FOREIGN DNA gets into a cell |
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Virion Protein Function |
Protection and Delivery of the viral genome |
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Meaning of Metastable |
Means that a viral capsid is stable enough to not fall apart outside of a cell, but will dissemble once inside a cell |
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Capsid |
Entirety of Protein Shell around genome/nucleid acid |
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Nucleocapsid |
Complete protein-nucleic acid complex in the virion |
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Envelope |
Host cell membrane around the virus/virion |
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Rules of Symmetry for Viral Self-Assembly |
Viruses need to have NONCOVALENT and IDENTICAL contact between subunits |
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Three Characteristics of an Icosahedron |
1. 20 Triangular faces; each an equilateral triangle (size of that triangle can vary to make capsid larger or smaller)
2. 12 vertices related by two, three and fivefold axes of rotational symmetry.
3. At least 60 identical subunits (60 is minimum); subunit numbers tend to be multiples of 60 |
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T-Number/Triangulation Number |
Signifies how many smaller triangle subunits make up one (of the larger 20) face(s) of an icosahedron; the larger the t-number the bigger the capsid
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How big are capsid proteins usually? |
20-60 kDa |
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Function of viral envelope proteins |
They can be used for attachment and/or fusion to host cells or as antigenic determinants to interact with immune system |
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Structured Envelope |
Envelope that has the same T= icosahedral structure as the underlying icosahedron via anchoring to the capsid under the membrane |
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Virion/Cell Attachment |
Enveloped virions attach through a receptor protruding out the membrane; non-enveloped virions attach through canyons (receptors) in the icosahedral structure |
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Viral Membrane Fusion Regulation |
Usually done through pH or proteolytic cleavage.
For class 1 fusion proteins, membrane fusion is regulated by proteolytic cleavage.
For class 2 fusion proteins, membrane fusion is regulated by cleavage of a second protein. Low ph (in endosomes) may also trigger fusion. |
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Virion Movement Within a Cell |
Virions = too big to diffuse through a cell, so must use cell transport machinery (endosomes, microtubules etc) |
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Which genomes bring an RDRP with them? |
dsRNA and -ssRNA both bring RDRPs with them into the host cell |
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How are proteins encoded in viral RNA genomes? |
Proteins are encoded in different genome fragments (influenza), production of subgenomic mRNAs (rabies) or translated in one long strand that is self-cleaving (poliovirus) |
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Where does influenza replication occur? |
In the nucleus of the host cell - exception to the RNA virus rule |
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How is poly(A) added to mRNAs? |
Through stuttering (where the RNA polymerase stays still and the template just keeps skipping back to repeatedly read the Us) or through reiterative copying (when the RNA polymerase encounters a stop-polyadenylation signal to repeatedly add groups of 7 As) |
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Viral RNA synthesis as a source of diversity |
No proofreading - often mistakes are made every few 1000-10000 nucleotides |
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Where do DNA viruses replicate? |
Usually in the nucleus of the host cell (specifically host replication centers) |
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Why is DNA viral replication always delayed after infection? |
The Replication machinery must be made first – transcription of genetic info that encodes some proteins necessary to replicate the viral genome or manipulate the cell to do so must be made
ex. sometimes DNA polymerase is stolen from the cell rather than encoded in the viral genome |
