The virus, lacking the enzymes and metabolic precursors necessary for its own replication, they must obtain them from the host cell they infect. Viral replication is a process that includes several separate synthesis and subsequent assembly of all components to give rise to new infectious particles. Replication is initiated when the virus enters the cell: cellular enzymes remove the cover and the DNA or RNA is contacted with the ribosome, directing the synthesis of proteins. The virus nucleic acid autoduplicates and, once synthesized protein subunits that form the capsid, the resulting components are assembled into new viruses. A single virus particle can cause a progeny of thousands. Some viruses are released by destroying the infected cell, and yet leave the cell without destroying it by a process of exocytosis that leverages own cell membranes. In some cases the infection is ‘silent’, ie the viruses replicate inside the cell without evident harm.

RNA-containing viruses are unique replicative systems, since the RNA autoduplicates without the involvement of DNA. In some cases, viral RNA functions as messenger RNA, and replicates indirectly using the ribosomal system and the metabolic precursors of the host cell. In others, the virus carried in the cover-dependent RNA enzyme that directs the synthesis process. Other RNA viruses, retroviruses, may produce an enzyme that synthesizes DNA from RNA. Formed DNA then acts as the viral genetic material.

During an infection, bacteriophages and animal viruses differ in their interaction with host cell surface. For example, in the cycle of bacteriophage T7, which infects the bacterium Escherichia coli, there are no stages or descapsidación adsorption. The virus binds first to the cell and then injects its DNA into it. However, once the nucleic acid enters the cell, the basic events of viral replication are the same.

4. Viruses in Medicine

Viruses represent a major challenge to medical science in combating infectious diseases. Many viruses cause major human diseases and diversity.

Among viral diseases include the common cold, which affects millions of people each year. Other diseases have serious consequences. Among them is rabies, hemorrhagic fevers, encephalitis, polio and yellow fever. However, most disease-causing viruses that cause severe discomfort only, provided that the patient will not be serious complications. Some of these are influenza, measles, mumps, fever with fever (herpes simplex), chickenpox, shingles (also known as herpes zoster), respiratory diseases, acute diarrhea, warts and hepatitis. Other viral agents as the cause of rubella (German measles) and cytomegalovirus, may cause serious anomalies or abortions. Acquired immunodeficiency syndrome (AIDS) is caused by a retrovirus. There are two known retrovirus associated with certain human cancers and is suspected of some forms of papillomavirus. There is evidence, increasingly, of viruses that might be involved in some types of cancer, chronic diseases such as multiple sclerosis and other degenerative diseases. Some viruses take a long time to cause symptoms, and produce so-called slow virus diseases such as Creutzfeldt-Jacob disease and kuru, which gradually destroys the brain.

Even today you find viruses responsible for important human diseases. Most can be isolated and identified with current methods of laboratory, although the process normally takes several days. One of them is rotavirus gastroenteritis caused by the child.

credit to: Martín Buczyner

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