Virology. Properties of Viruses. Contain a single type of nucleic acid, either DNA or RNA, not both. The DNA and RNA can either be double stranded (ds) or single stranded (ss) depending upon the virus. Surrounded by a protein coat called a capsid.
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Spikes can mutate and then the virus can reinfect the same individual. Influenzavirus is an example of a virus that does this.
Viruses multiply inside living cells using cell machinery to replicate nucleic acid and make proteins.
Viruses cause synthesis of specialized structures that can transfer viral nucleic acid to other cells
General Morphology Spikes are protein or carbohydrate complexes used for attachment to the target cell.
There are some general shapes that animal viruses tend to have.
Helical: see figure 6.5 for a great description of this structure.
Polyhedral: has multiple sides. An example of a polyhedral shape is icosahedral.
Complex virus: this is a virus that does not fit into one of the above categories. An example of this kind of virus would be a bacteriophage
Virion Spikes are protein or carbohydrate complexes used for attachment to the target cell.: A virion is a complete, fully developed, infectious viral particle.
Host Range: Each virus has a different host range. The host range is the number of different host cells a virus can infect.
The attachment proteins on the outside of the virus determine the host range for a virus. If they are compatible with proteins on the host cell membrane found on many cells then the host range will be large. If the viral proteins are only compatible with a protein found on a few host cell membranes then the host range will be small.
Cultivation Spikes are protein or carbohydrate complexes used for attachment to the target cell.
Since viruses are obligate intracellular pathogens tissue cultures have to be grown in order to cultivate viral particles.
Tissue cultures are started with small tissue samples of organs that viruses are known to infect, such as kidney or lung cells.
Primary cell line: The initial tissue sample that is used to start a tissue culture, derived from tissue slices is called the primary cell line.
Generally tissue samples last only a few generations.
Continuous cell lines Spikes are protein or carbohydrate complexes used for attachment to the target cell.: transformed, or altered, cells (cancerous) can be maintained through an indefinite number of generations. Essentially a cancerous cell is one in which the programmed cell death response has been turned off. The cell will grow and divide indefinitely.
Cytopathic effect: When tissue cultures are grown, the cells grow in a single layer, called a monolayer, on the bottom of a plastic flask. When the tissue monolayer is infected with a virus it will cause cell deterioration. The changes in the appearance of the cells and the monolayer as a whole are called cytopathic effects. The changes in the cells and monolayer can be used for diagnosis for some viruses because they will create a distinct change.
For example, RSV (respiratory syncytial virus) causes the infected cells to join together forming large cells with many nuclei.
Synthesize capsid and other viral components in cytoplasm using host cell enzymes
5. Assembly: capsid is formed and the nucleic acid is inserted.
6. Release: cell is lysed and virions are free.
Enveloped viruses will push through the membrane instead of breaking the cell open. The host cell membrane contains viral protein spikes that then surround the virion when it pushes through the membrane.