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Unformatted text preview: Legends – Virology Diagrams Vir. – 1. Basic virus structures. The capsid consists of a number of protein subunits (capsomers) that surround the nucleic acid, or a nucleoprotein complex or a core. Depending on the particular virus, the nucleic acid genome of the virus may be DNA or RNA (DNA and RNA are never found together inside the virus capsid). Depending on the particular virus, enzymes involved in the replication of the genome maybe associated with the genome. Many animal viruses also have lipid envelopes surrounding the nucleocapsid. These envelopes are derived from a membrane derived from the replication cycle within the previous host cell. The viral envelopes are often modified by the insertion of viral-encoded glycoprotein. Vir. – 2. The Baltimore Classification. This system describes the formation of viral mRNA by different classes of viruses after the virus has infected the cell. The polarity of their genomes [i.e., (+) or (-) designations] are based on the molecular biologist's conventions, with (+) RNA being considered as the equivalent of mRNA. The enzymes required in the replication cycle that lead to the synthesis of viral mRNA are indicated. Vir. – 3. Generation of Primary and Transformed Cell Cultures. A common method to obtain single cell suspensions from primary tissue (e.g., muscle biopsy sample) is by mechanical teasing and treatment with protease enzymes such as trypsin to disperse the cells. The cells are then incubated in a tissue culture dish with nutrient-rich growth media enriched with blood serum. A transformed cell line can divide indefinitely in vitro . Primary cultures will frequently divide a limited number of times (due to their inherent programming) and also might contain different cell types. Transformed cell lines are frequently derived from single cells, thus ensuring a culture with uniform genetic composition, growth characteristics and susceptibility to infection. Vir. – 4. The Quantitation of a Virus Stock Using the Plaque Assay . Cells are grown in a monolayer and infected with virus. After virus infection and replication, the cells are lysed leaving a “plaque” or clearing in the lawn of confluent cells. The plaques can be visualized after fixing and staining the cells. The number of plaques is counted, and this number is multiplied by the dilution factor to determine the concentration of virus in the original stock. Vir. – 5. Virus Induced Cytopathic Effects. Cytopathic effects are damage to infected host cells caused by infecting viruses. Basically, the viral infection results in cell abnormalities (biochemical and morphological) and/or cell death as a consequence of the virus' metabolic needs and those of the host cell simply not completely corresponding....
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