virion /vir″ē·on, vī″rē·on/ [L, virus, poison] , a single virus particle with a central nucleoid surrounded by a protein coat or capsid. The complete nucleocapsid with a nucleic acid core may constitute a complete virus, such as the adenoviruses and the picornaviruses, or it may be surrounded by an envelope, as in the herpesviruses and the myxoviruses. Such an envelope is a membrane that contains lipids, proteins, and carbohydrates and projects spikelike structures from its surface. See also capsid.
