A virus alternates between two forms, an inert virus particle, the virion, which survives outside the host cell, and an active intracellular stage. The life cycle of a typical virus goes through the following stages (Fig. 17.03):
a. Attachment of virion to the correct host cell b. Entry of the virus genome c. Replication of the virus genome d. Manufacture of the virus proteins e. Assembly of new virus particles (virions)
f. Release of new virions from the host cell
Attachment of a virus requires a protein on the virus particle to recognize a molecule on the surface of the target cell. Sometimes this receptor is another protein; sometimes it is a carbohydrate. Often it is a glycoprotein, that is a protein with carbohydrate groups attached. On some virus particles, the recognition proteins form intracellular parasite Parasite that lives inside the cells of its host organism parasite An organism or infectious agent that uses the resources of another organism in order to grow and multiply
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