Chapter 21
Viruses
By Boundless
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Viruses are infectious particles about 100 times smaller than bacteria and can only be observed by electron microscopy.
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The evolution of viruses is speculative as they do not fossilize; biochemical and genetic information is used to create virus histories.
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Viruses of all shapes and sizes consist of a nucleic acid core, an outer protein coating or capsid, and sometimes an outer envelope.
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Viruses are classified by factors such as their core content, capsid structure, presence of outer envelope, and how mRNA is produced.
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Viral infection involves the incorporation of viral DNA into a host cell, replication of that material, and the release of the new viruses.
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Bacteriophages, viruses that infect bacteria, may undergo a lytic or lysogenic cycle.
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Animal viruses have their genetic material copied by a host cell after which they are released into the environment to cause disease.
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Plant viruses can cause damage to stems, leaves, and fruits and can have a major impact on the economy because of food supply disruptions.