Virus

Abstract

Viruses are minute infectious agents that multiply by infecting living cells, where they convert the cellular apparatus into a factory for making more viruses. A virus particle, or virion, consists of a nucleic acid genome, either DNA or RNA, enclosed in a protein covering, the capsid; the combination of a viral genome and its capsid is the nucleocapsid; in some viruses, this is further enclosed in an envelope derived from membranes of the cell in which the virion was formed. The viral genome encodes proteins of the capsid along with enzymes and other proteins for directing multiplication. A virus typically inserts its genome into an appropriate host cell and multiplies rapidly, after which the cell lyses or disintegrates. Some viruses, however, are able to establish a condition of lysogeny in which the viral genome remains quiescent within the cell, often integrated into its cellular genome, multiplying as the cell reproduces. In large organisms such as plants and animals, viral infection is typically seen as a disease process.