A. CHARACTERISTICS OF VIRUSES
The overall purpose of this Learning Object is to introduce the general characteristice of viruses and how they may be cultivated in the laboratory.
LEARNING OBJECTIVES FOR THIS SECTION
General Characteristics of Viruses
Viruses are infectious agents with both living and nonliving characteristics. They can infect animals, plants, and even other microorganisms. Viruses that infect only bacteria are called bacteriophages (def) and those that infect only fungi are termed mycophages (def).
1. Living characteristics of viruses
a. They reproduce at a fantastic rate, but only in living host cells.
b. They can mutate.
2. Nonliving characteristics of viruses
a. They are acellular, that is, they contain no cytoplasm or cellular organelles.
b. They carry out no metabolism on their own and must replicate using the host cell's metabolic machinery. In other words, viruses don't grow and divide. Instead, new viral components are synthesized and assembled within the infected host cell.
c. TThe vast majority of viruses possess either DNA or RNA but not both.
3. Criteria used to define a virus
a. The vast majority of viruses contain only one type of nucleic acid: DNA or RNA, but not both.
b. They are totally dependent on a host cell for replication. (They are strict intracellular parasites.)
c. Viral components must assemble into complete viruses (virions) to go from one host cell to another.
4. Laboratory cultivation of viruses
Since viruses lack metabolic machinery of their own and are totally dependent on their host cell for replication, they cannot be grown in synthetic culture media. Animal viruses are normally grown in animals, embryonated eggs, or in cell cultures where in animal host cells are grown in a synthetic medium and the viruses are then grown in these cells.
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Updated: July 12, 2006
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