The term latency is used to denote the interval from infection to clinical manifestations. This carrier state can take any of several different forms. Some viruses do not produce rapid lysis of host cells, but rather remain latent for long periods in the host before the appearance of clinical symptoms. Some envelope proteins facilitate viral entry into the cell, and others have directly pathogenic effects. Although in general viruses вЂњstealвЂќ their lipid envelope from the host cell, virtually all of them produce вЂњenvelope proteinsвЂќ that penetrate the envelope and serve as receptors. But no virus has the thousands of genes required by even the simplest cells. Other more complex ones may have a few hundred genes. Some viruses have only a few genes coding for capsid proteins. When these proteins assemble to form the capsid, part of the host cell membrane is pinched off to form the envelope of the virion. In viruses that have membranes, membrane-bound viral proteins are synthesized by the host cell and move, like host cell membrane proteins, to the cell surface. Reverse transcriptase is actually a combination of two enzymes: a polymerase that assembles the new DNA copy and an RNase that degrades the source RNA. In other viruses a reverse transcriptase contained in the virion transcribes the genetic message on the viral RNA into DNA, which is then replicated by the host cell. For certain viruses the RNA is replicated by a viral enzyme ( transcriptase) contained in the virion, or produced by the host cell using the viral RNA as a messenger. Some of these may already have been present within the initial virus, and others may be coded for by the viral genome for production within the host cell.Д«ecause host cells do not have the ability to replicate вЂњviral RNAвЂќ but are able to transcribe messenger RNA, RNA viruses must contain enzymes to produce genetic material for new virions. These are the proteins that form the capsid (protein coat) there may also be a few enzymes or regulatory proteins involved in assembling the capsid around newly synthesized viral nucleic acid, in controlling the biochemical mechanisms of the host cell, and in lysing the host cell when new virions have been assembled. Within the host cell the genetic material of a DNA virus is replicated and transcribed into messenger RNA by host cell enzymes, and proteins coded for by viral genes are synthesized by host cell ribosomes. (Some do contain or produce essential enzymes when there is no cellular enzyme that will serve.) When a complete virus particle ( virion) comes in contact with a host cell, only the viral nucleic acid and, in some viruses, a few enzymes are injected into the host cell. Unlike cellular organisms, viruses do not contain all the biochemical mechanisms for their own replication they replicate by using the biochemical mechanisms of a host cell to synthesize and assemble their separate components. A virus consists of genetic material, which may be either DNA or RNA, and is surrounded by a protein coat and, in some viruses, by a membranous envelope. Because these properties are shared by certain bacteria ( rickettsiae, chlamydiae), viruses are now characterized by their simple organization and their unique mode of replication. Any member of a unique class of infectious agents, which were originally distinguished by their smallness (hence, they were described as вЂњfiltrableвЂќ because of their ability to pass through fine ceramic filters that blocked all cells, including bacteria) and their inability to replicate outside of and without assistance of a living host cell.

Computer virus names