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28 Cards in this Set
- Front
- Back
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What is a capsid? What shapes can it take on?
What are the functions of the capsid? |
Capsid = protein coat enclosing genome
Either helical (rod-shaped/coiled) or icosahedral (spherical/symmetrical) Capsid packages, protects, and transports nucleic acids. Also provides specificity for attachment to specific receptors. |
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With regard to helical symmetry, what is a protomer?
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Successive polypeptide unit that nucleic acid is wound around to form a helix (via H-bonding)
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With regard to icosahedral symmetry, what is a capsomere?
What determines the size of an icosahedral virus? |
Polypeptide subunit h-bonded to each other to form icosahedron (12 vertices, 20 triangular faces)
(Nucleic acid within empty space.) Number of capsomeres determine size of virus. |
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What are the contents of a viral envelope? Function?
What is the effect of envelopes on environmental stability? |
Viral envelope consists of a lipid bilayer containing glycoproteins derived from host cell membrane.
Envelope surrounds nucleocapsid. Glycoprotein spikes mediate attachment and penetration in host cells. Envelopes render virus more fragile and susceptible to desiccation, detergents, EtOH, and enzymes. Non-enveloped virus = NAKED virus |
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How does DNA location differ between icosahedral and helical viruses?
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In an icosahedral virus, DNA is contained within empty space created by capsomeres.
In a helical virus, DNA is associated intimately with capsomeres. |
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What is a virion?
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Complete virus particle
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Structural vs Nonstructural Protein
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Structural: viral protein that is part of the virion
Nonstructural: proteins involved in viral replication |
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All RNA viruses are _________
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helical
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All DNA viruses are _________
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icosahedral with envelope
EXCEPT POXVIRUS!!! |
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Herpes Simplex Virus vs Human Papillomavirus: Host Range
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HPV has a smaller host range than HSV because it can only infect human epithelial cells
Host range = the kind of cells, tissues, and species that a virus can infect and produce a progeny. |
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What is a major determinant of host range and tissue tropism?
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Presence or absence of receptors!
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What is tissue tropism?
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Cells that a virus can readily infect.
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What occurs during the attachment phase of viral replication?
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Attachment = Absorption
Virus binds receptors on host cell membrane |
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Describe the three methods of penetration during viral replication.
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1) Direct penetration into host cell
2) Receptor-mediated endocytosis (viropexis): after absorption, endocytotic vesicle (endosome) encloses virus. low pH of endosome (!!!) leads to fusion of viral envelope with endosomal membrane and release of nucleocapsid into cytoplasm. Naked viruses also enter by this method, ex: poliovirus 3) Direct membrane fusion: glycoprotein spikes promote fusion of viral membrane with plasma membrane of cell |
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What occurs during the uncoating phase of viral replication? How does this stage differ among DNA and RNA viruses?
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Disassembly of virion and subsequent release of nucleic acid.
Genome of DNA viruses (EXCEPT POXVIRUS) must be delivered to the nucleus Most RNA viruses remain in cytoplasm (EXCEPT influenza and RETROVIRUSES which replicate in the nucleus) |
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Replication, Transcription, and Translation requirements for:
DNA Viruses RNA Viruses Retroviruses Include subcategories for each (ss, ds, +/-) |
End goal is to produce virus-specific mRNA in order to replicate
ss/ds DNA use host cell DNA-dependent RNA polymerase to make mRNA, and host cell DNA-dependent DNA polymerase for replication RNA viruses must produce their own RNA-dependent RNA polymerase ssRNA+: identical to mRNA, immediately translated, contains template for RNA-dependent RNA polymerase to synthesize ssRNA+ strands to amplify capacity to produce virion proteins ssRNA-: complementary to mRNA, virus must package enzyme to produce positive strands Retroviruses: ssRNA+ strand converted to a dsDNA by RNA-dependent DNA polymerase (REVERSE TRANSCRIPTASE) contained in virion. Resulting dsDNA integrated into cell genome by INTEGRASE. Transcription mediated by host cell RNA polymerase. |
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Early vs Late Genes
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Early: transcribed before DNA replication begins; involved in DNA replication (starts out as DNA in nucleus, to mRNA, to proteins in cytoplasm, back to nucleus)
Late: transcribed after initiation of DNA replication; most are structural proteins incorporated into progeny virus particles (Early prots replicate progeny DNA, which turn into mRNA, then late proteins in cytoplasm, then assembled into nucleocapsids) |
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Are larger viruses more or less dependent on host cell functions? Why?
What is the effect of this on antiviral susceptibility? Provide examples of large viruses. |
Larger viruses are LESS dependent on host cell fns bc they're able to encode larger number of genes
Larger viruses more susceptible to antiviral chemotx bc more virus-specific processes available as targets for drug action Ex of larger viruses: herpesviruses, poxviruses |
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What are the two forms of protein coding in ssRNA- viruses?
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1) Genome may be polycitronic in which number of mRNAs are produced that encode single polypeptides
2) Genome may be segmented where each segment corresponds to a single gene |
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How are proteins coded in dsRNA viruses?
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Segmented coding with each segment encoding for a single polypeptide.
Virus must bring RNA-dependent RNA polymerase. (+) RNA transcripts used for translation and as templates for complementary (-) strand synthesis for dsRNA progeny. |
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Where does the assembly stage of viral replication take place?
How does this differ between naked and enveloped viruses? |
Assembly of nucleocapsids takes place at site of viral replication (for most DNA viruses, capsid proteins transported from cytoplasm to nucleus)
Naked viruses: virion is complete after assembly Enveloped viruses: most bud from host membrane: viral envelope proteins incorporated into HOST cell membrane, cytoplasmic domains of inserted proteins associate with additional viral proteins (matrix proteins) to which nucleocapsid binds, nucleocapsid enveloped (budding).Process continues until cell loses ability to maintain plasma membrane integrity. |
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What is pathogenesis?
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Mechanism by which virus causes host injury.
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What is virulence?
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Degree to which infectious agent is pathogenic.
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What is a syndrome?
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Specific group of signs and symptoms (clinical disease)
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What is a cytopathic effect? Examples?
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CPE: virus-induced cellular changes visible under microscope
Ex: Cell rounding or lysis, vacuolation, formation of MULTINUCLEATED GIANT CELLS (SYNCYTIA) formed by viral fusion of neighboring cells, inclusion bodies in cytoplasm/nucleus Different viruses produce different CPE's |
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Describe the following viral infections:
Acute Latent Chronic |
Acute: virus reproduces rapidly in cells and leads to cell lysis
Latent: Persistence of viral genome inside a host cell with no production of progeny; variety of stimuli lead to reactivation months to years later leading to productive infection Chronic: low levels of virus continually produced after period of acute illness. Cells producing virus are not killed and immunity is insufficient to eliminate virus. |
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What is viremia?
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Presence of virus in blood stream (invasion followed by localized replication at primary site), virus can then infect cells at secondary sites.
Remember: viruses tend to exhibit organ and cell specificities. |
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What is the most important host factor affecting viruses?
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Immune Response: determines whether virus is cleared or not
Sometimes the immune response itself is responsible for damage! |
