Virus Reproduction

Viruses reproduction begins when the virion comes into contact with a suitable host cell. The DNA or RNA enters the host cell and begins to function as genetic information by directing the synthesis of specific types of proteins that have enzymatic and structural roles. The infectious cycle usually consists of two different stages. In the first, the proteins are produced that are required for the reproduction of the viral DNA or RNA in conjunction with components of the host cell. In the second stage, proteins that make up the virion are produced; these combine with the DNA or RNA to form mature virions, which are the released from the cell. In some cases this release involves the complete disruption and death of the cell, a process known as lysis. In other cases individual virions are released through the cell membrane without killing the cell.

A virus contains the information needed to reproduce itself coded in its nucleic acid. Because it lacks its own protein producing machinery, however, the virus must use the machinery of the host cell in order to multiply. A bacteriophage virion attaches to a bacterial cell and injects its DNA into the bacterium. Using bacterial ribosomes enzyme the viral DNA direct the synthesis of messenger RNA (mRNA), enzymes that break up bacterial DNA, and enzymes that allow replication of viral DNA. Protein synthesized, using mRNA, from the DNA code, these proteins from heads, tails, and tail fibers, and the virus parts assemble into complete virions. An enzymes break up the bacterial cell and liberates the new virions, which can infect other bacterial cells. The information that bring by DNA will procude a virus with the same virus characteristic.

Virus History

Viruses History

Viruses were discovered at the end of the 19th century. In 1892, Dimitri Ivanovsky, a Rusian botanist, discovered that the sap from tobacco plants affected by mosaic diseases could be passed through filters so fine as to exclude all known bacteria and still retain the ability to produce the diseases in new plants. In 1898, Frederich Loeffler and Paul Frosch reported similar results for the infectious agent of foot-and-mouth diseases of cattle. They also showed that an animal inoculated with a tiny amount of filtered material could itself subsequently give rise to a very potent inoculums. This indicated that the infectious agent was able to reproduce itself within the infected animal. During the next three decades many viruses were discovered. Unlike other microorganisms, none of the viruses could be propagated in the absence of host cells, which led researchers to conclude that viruses are intracellular parasites.

Beginning in the 1930s, a number of new techniques were developed for virology, or the study of viruses. The discovery that many animal viruses can be grown in mice and in chicken embryos allowed the course of viral infection to be studied under controlled laboratory conditions. Very high-speed centrifuges were developed that made possible the preparation highly purified virions. Chemical analysis showed that viruses consist primarily of nucleic acid and protein, and the development of the electron microscope during the 1940s permitted scientists to study the size and shape of these virions in great detail.

Because of the ease with which bacteria can be grown and manipulated in the laboratory, many of the features of intracellular viral development were first discovered by studying bacteriophage, which are viruses that grow in bacteria. During the late 1950s techniques for growing animal cells in tissue culture were developed, making possible the detailed study of the intracellular growth of animal viruses.