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32 Cards in this Set

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  • Back
What are 5 characteristics of viruses?
1. Can'tsee w/ lite microscope
2. Have to use EM
3. Obligately intracellular
4. Have RNA/DNA, not both
5. Don't respond to antibiots
What is the smallest/largest virus?
Smallest = Polio

Largest = Pox
What are 4 characteristics of viral structure?
1. Nucleocapsid
2. Virion vs. viroid
3. Naked vs. Enveloped
4. Symmetry
What is the nucleocapsid?
the nucleic acid and capsid
What is a virion?
What is a viroid?
Virion = virus w/ complete capsid and nucleic acid.

Viroid = incomplete, doesn't have a capsid.
What is an Envelope?
How does it form?
extra outer layer - a capsule.
-Formed by picking up some membrane during budding of virus from host cell.
What are the 2 types of symmetry?
1. Icosahedral (cubic)

2. Helical (coiled)
What are the 6 steps in Viral replication?
1. Adsorption
2. Penetration
3. Uncoating (eclipsing)
4. Nucleic acid replic/protein coat synthesis.
5. Assembly
6. Release
What occurs in adsorption?
Ads: viruses binds to host cells w/ the receptor for it.

Pen: by phagocytosis or melding
What occurs in Uncoating?
Eclipsing - the cell's enzymes release the nucleic acid from the capsule.
What occurs in the course of viral nucl. acid replication and protein synthesis?
the viral nucleic acid is replicated using the host's machinery, and new capsomeres are synthesized (protein) to make the capsid.
What is interesting about the assembly process of viruses?
It is the least efficient step in the whole replication process.
What happens if viral assembly is incomplete?
Pieces get left in the host cell and can be seen on a tissue biopsy as INCLUSION BODIES.
Where does a DNA or RNA virus assemble?
DNA = in the host's nucleus

RNA = in the host's cytoplasm.
How is the virus released after assembly and all?
It depends on the type of virus - whether enveloped or not.
How does each release:
-Env released by budding

-Naked released by lysis.
What are the 5 steps in viral infection of host cells?
1. Transmission
2. Port of entry
3. Binding to specific receptor
4. Active infection
5. Latent infection
What type of viruses especially cause latent infections?
DNA viruses - like the herpes virus w/ cold sores.
what is a latent viral infection in bacteria called?
How does lysogeny affect C. diphtheriae?
The virus encodes the exotoxin produced by the bacteria, and is released upon lysis.
What are 3 host defenses to viruses?
1. Humoral
2. Cellular
3. Interferon
How does each defense work -Humoral
Humoral Prevents infection
Cellular helps recover
Interferon is species spcf and prevents a runaway infection.
How does interferon prevent spread of infection?
It is released from infected cells and protects neighbors.
What are 7 methods for identifying viruses?
1. Tissue cultures (CPE)
2. Shell vial assays
3. Animal/chick embryo inoculat.
4. Cytological exam of host tissue
5. Immunological tests
6. Serological tests
7. molecular methods
What is CPE?
Cytopathic effect
What are 6 effects viruses can have on host cells?
1. None
2. Inclusion bodies
3. Giant cells
4. Cell death
5. Proliferation
6. Chromosomal changes
What does the location of an inclusion body tell about the virus?
-If in nucleus of cells, its a DNA virus
-If in cytoplasm, an RNA virus.
How do viruses cause giant cells?
by causing nuclear divisions without cytoplasmic.
What's an example of prolif caused by a virus?
How do you do a tissue culture?
-Put down a monolayer of cells.
-If tube, use roller drum to keep virus on all cells.
-Look for CPE
What is a shell vial assay, how is it done?
1. monolayer of cells on coverslip
2. add specimen; centrifuge at 35 for 30-45 minutes
3. Incubate for 24 hrs
4. Flood with Ab-flour
5. Incubate, wash, UV scope
What information is being sought when identifying viruses?
-Time takes for growth
-Cytopathic effect it has
-Type of cell line it grows on