Viral genetic material

Expression of the Viral Genetic Material. This occurs during the eclipse period, when the amount of infectious virus appears low. Several events occur during the eclipse phase ... 

Replication of the viral genetic material. The virus programs the machinery necessary to generate more copies of its own genetic material. In some cases, this may rely on the machinery from the infected cell, but in other cases, the virus may specify proteins that are necessary for the process. 

Penetration and Uncoating. The virus enters the host cell either by passing directly through the cell membrane or by fusing with the host-cell membrane and releasing the viral genetic material into the host cell. Once inside the host cell, its proteolytic enzymes usually remove any coating that remains on the virus. 

Biosynthesis. When viral genetic material is released within the host cell, the virus takes control of the cell s molecular synthesizing machinery to initiate the biosynthesis of new viral enzymes and proteins. Different viruses exert their effects on the host cell in... 

Mechanism of Action. Acyclovir inhibits viral DNA replication by inhibiting the function of the DNA polymerase enzyme.42 This drug is taken into virus-infected cells and converted to acyclovir triphosphate by an enzyme known as viral thymidine kinase 42 The phosphorylated drug directly inhibits the function of the viral DNA polymerase, thus impairing the replication of viral genetic material. The virus also incorporates the drug into viral DNA strands, which halts further production of DNA because of the presence of a false nucleic acid.42... 

Viral particle production processes by cell culture infection, cannot be characterized in such a simple way, since the final product - virus -does not result from a secondary metabolic pathway. However, it can be better described as a process redirecting the cell machinery towards viral particle production, which only happens after viral infection. The virus production process can be divided into two different steps. The first involves cell multiplication, which results from the conversion of culture medium substrates into cell mass. At the instant of viral infection, the cellular production unit no longer exists, since the viral genetic material forms a new production unit, initiating the second step of the virus production process. This production unit is the infected cell and is the producer of new viral particles. This production phase requires nutritional and metabolic conditions that are not observed during cell growth. These conditions are normally studied separately. Nevertheless, virus production... 

Because viruses cannot grow or reproduce on their own, they are not considered to be alive. To survive, a virus must infect a host cell and take over its internal machinery to synthesize viral proteins and in some cases to replicate the viral genetic material. When newly made viruses are released, the cycle starts anew. Viruses are much smaller than cells, on the order of 100 nanometer (nm) in diameter in comparison, bacterial cells are usually > 1000 nm (1 nm= 10 meters). A virus is typically composed of a protein coat that encloses a core containing the genetic material, which carries the information for producing more viruses (Chapter 4). The coat protects a virus from the environment and allows it to stick to, or enter, specific host cells. In some viruses, the protein coat is surrounded by an outer membrane-like envelope. 

Viral infections are normally overcome by the patient s immune system. However, the advent of HIV infections and AIDS has led to the development of several new antiviral drugs. Antiviral drugs work by inhibiting the synthesis of viral DNA, RNA or proteins by reducing the release of viral genetic material inside host cells by interfering with viral penetration of host cell membranes and by interfering with attachment of virus to host... 

HIV-1 invades and destroys the CD4 positive cells of the immune system. Like other retroviruses, the life cycle requires incorporation of viral genetic material into the host genome. Subsequent transcription and translation events generate virus progeny. Release of the new virus particles is fatal to the host CD4 positive cell. A gradual depletion of immune cells occurs over a period of years and compromises the immune response to the extent that infections that normally would be relatively benign can become life threatening and deadly. 

Because viruses contain RNA and not DNA, replication of viral genetic material is not subject to the same error-checking and repair mechanisms as is cellular DNA. Thus, mutations in viral RNA are relatively more common, and viruses, should they be able to survive the mutations, can evolve rather quickly to circumvent cellular or therapeutic drug antiviral countermeasures. Antiviral defenses oftentimes recognize viral surface proteins as foreign bodies, and deal with them accordingly. Cytokines... 

Most recently (36) another drug [9-(2-hydroxyethoxymethyl)guanine] has been described which inhibits herpes simplex virus replication without affecting any virus infected cells. The basis of selectivity appears to depend upon the ability of the drug to be phosphorylated (by a virus-coded thymidine kinase) to compounds which are toxic to the viral genetic material. 

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