Lecture 24: Virus Structure Flashcards
What are obligate intracellular parasites?
Organisms that can’t reproduce outside of cells
What do viruses require from host cells?
- Energy
- Components for synthesis of proteins & nucleic acids
- Ribosomes & some enzymes
What is a common characteristic of all viruses?
All contain one type of nucleic acid
What types of nucleic acids can viruses have?
- ss RNA (+ or - strand)
- ss DNA (+ or - strand)
- ds RNA
- ds DNA
What is a capsid?
A protein coat surrounding the viral nucleic acid
What are the shapes of viral capsids?
- Helical
- Icosahedral
- Complex, all other shapes
What is an envelope in the context of viruses?
An outer lipid bilayer membrane surrounding the capsid
How are viruses categorized?
- Genome
- Capsid
- Envelope
- Host type
- Diameter of virion
- Immunogenic properties
- Intracellular location of replication
- Disease caused & mode of transmission
What is the typical diameter of a virion?
~ 10-300 nm
What is the purpose of cultivation in virology?
To grow viruses in cells
What are two methods for isolating viruses?
- Differential Centrifugation
- Gradient Centrifugation
What does Differential Centrifugation involve?
Two spins: 1st spin at ~8,000 rpm to remove large cells, 2nd spin at ~100,000 rpm to remove virus
What does Gradient Centrifugation use to isolate viruses?
Sucrose density gradient
How can viruses be quantified?
- Electron microscope
- Plaque assays
- Hemagglutination assays
- Immunohistochemistry
What does a plaque assay measure?
The cytopathic effect of viruses
What is the ELISA test used for?
To test for antibodies against a virus
In an ELISA test, what is the first step?
Coat petri dish with viral proteins
What does PCR stand for?
Polymerase chain reaction
What does a PCR test detect?
Viral nucleic acids in cells
What is a potential problem with antibody tests?
Some people do not produce antibodies for up to 6 months
True or False: Some viruses can cause red blood cells to agglutinate.
True
