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Define virion, prion, and viroid, and phage
- Virion: complete, infectious virus
- Prion: Infectious protein
- Viroid: Infection RNA (plant pathogen)
- Phage: virus that infects bacteria
Describe morphological classes of viruses and give an example of each
- Helical viruses: long rods with hollow cylindrical capside (Ebolavirus, rabiesvirus)
- Polyhedral viruses: many-sided capsids (adenovirus, poliovirus)
- Complex viruses: has additional structure attached to capsid (bacteriophage T4)
Define plaque forming unit, Explain the plaque method (its uses and procedures)
- Viruses must be grown in living cells
- Plaque: clearing in plate caused by lysing of bacteria as viruses multiply
- PFU: theory that each plaque initially came from a single virus
- Plaque method: PFUs counted and viruses determined in that manner
Define lysogenic conversion and give examples of diseases that result from this
- Lysogenic (phage) conversion: host cell exhibits new properties (production of toxins by prophage)
- Scarlet fever, diptheria, and botulism can result
List and describe the 5 steps of viral multiplication (lytic cycle)
- Attachment: phage attaches to host cell
- Penetration: phage penetrates host cell and injects DNA
- Biosynthesis: Phage DNA directs synthesis of viral components by the host cell
- Maturation: viral components are assembled into virions
- Release: host cell lyses, and new virions are released
Compare and contrast lytic and lysogenic cycles
- Lytic cycle: phage DNA not incorporated into host DNA, causes lysis and death of host cell
- Lysogenic: phage DNA incorporated in host DNA (prophage), host is not killed, phage conversion can occur, specialized transduction can occur upon excisement.
Differentiate between specialized and generalized transduction
- Specialized transduction: Prophage is within the chromosome. Excises innapropriately from the chromosome and takes a gene with it.
- Generalized transduction: Bacterial chromosome broken to pieces during viral construction, accidentally packaged into virus and released.
Explain the mechanism by which some viruses (retroviruses) induce tumors (cancer) give examples
- Lysogenic cyle integrates DNA into host's DNA, which can alter the nucleotide sequence forming infections and cancers.
- The cell recieves new properties which lead to increased growth and loss of contact inhibition.
- DNA viruses: adenoviridae, herpesviridae, poxviridae, palpvaviridae, hepadnaviridae
- RNA viruses: retroviridae, HTLV-1, HTLV-2
Explain the importance of reverse transcriptase and describe what occurs in the biosynthesis of a virus with reverse transcriptase
- Reverse transcriptase is necessary for retroviridae to infect the host cell. RNA is converted to DNA, and the DNA is inserted into the host cell's chromosome.
- The reverse transcriptase enzyme is packaged within the viral capsid during biosynthesis.
Describe how the following are cultured in the laboratory: bacterial viruses (bacteriophages), animal viruses
- Bacteriophages: plaque method (clearing zone is 1 PFU)
- Animal viruses: living animals, embryonated eggs, or cell culture (plants or animals)
List the major methods used for viral identification
- Cytopathic effects: destruction of cells
- Serological tests: detect antibodies against viruses in a patient (neutralization tests, viral hemagglutination, Western blot)
- Nucleic acids: RFLPs (similar to DNA fingerprinting), or PCR (specific viral sequences)