Data Bases • Custom Term Papers • Free Term Papers • Free Research Papers • Free Essays • Free Book Reports • Plagiarism? Links • Top 100 Term Paper Sites • Top 25 Essay Sites • Top 50 Essay Sites • Search 97,000 Papers @ DirectEssays.com • Search 101,000 Papers @ ExampleEssays.com • Search 90,000 Papers @ MegaEssays.com Free Essays • Term Paper Sites • Chuck III's Free Essays • Free College Essays • TermPaperSites.com • My Term Papers • Get Free Essays • Essay World • Planet Papers	Search Lots of Essays Back to Subjects - Science The Virus that Could Save Your Life The Virus that Could Save Your Life The existence of viruses has been known ever since 1892 when the virus that causes the tobacco mosaic virus was isolated. Viruses are defined as organic entities made up of merely some genetic material and a protective protein coating. Alone, viruses are considered to be "dead" or inanimate, but when they are inside a cell, they are able to replicate in massive quantities. Although they had long been known, a virus's size or shape was not known until the 1940's with the development of the electron microscope. Most viruses known to this day are, in some way, harmful; all are parasites. Recently, though, a certain type of viruses, retroviruses, have shown potential to be beneficial, even life saving, to humans. Except for a few small differences retroviruses are basically is the same as any other virus. Like all viruses, retroviruses contain a core of genetic material, but retroviruses contain only RNA (ribonucleic acid) never DNA (deoxyribonucleic acid). (Retroviruses) Instead of injecting a new genome of DNA into the host cell, the retrovirus uses RNA as the blueprint for a new genome. Surrounding this core of RNA is a capsid protein. This serves as a sort of capsule to hold the core of the virus together. Along with the RNA inside the capsid is an enzyme called reverse transcriptase. This allows the virus to replicate once it has infected the host cell, transcribing viral RNA into a new genome of DNA. This entire core, contained in the capsid protein, is again encapsulated in a lipid envelope. The first line of protection against the environment is this envelope. Stuck in this envelope are the receptor-binding proteins. These proteins are essential for the function of the virus. A virus can only infect a cell if the receptor-binding proteins match the surface proteins of the potential host cell. Only a cell with the exact match of proteins can become a victim to a retrovirus. (Retropages) HIV-1, for example, has an envelope protein that binds to CD-4 molecules. CD-4 molecules are most commonly found in human T-cells. (HIV Graphics) The entire life of a retrovirus consists of infecting cells to replicate new viruses. When a virus has no available cells to infect, it remains dormant. It can survive for great amounts of time in this dormant state. When the virus comes into contact with new living matter, it activates and again begins to replicate. Many types of retroviruses are known today. Undoubtedly the best known is the HIV virus, the virus that causes AIDS. The name for the family that both HIV-1 and HIV-2 belong to is the lentivirus family. A retrovirus known as HTLV-1 or HTLV-2 (human T-cell lymphotropic virus) along with a virus deemed BLV both belong to the family BLV-HTLV. When a retrovirus infects a host cell it must first find a cell with a match for in its surface proteins. After the virus has attached itself to the side of the host cell, it injects both the viral RNA and several copies of the enzyme reverse transcriptase. (Retropages) Without this vital enzyme, the viral RNA would be essentially useless. Reverse transcriptase is "a DNA polymerase that uses RNA as its template." In other words, the enzyme allows genetic information to flow in reverse from the normal. DNA is usually transcribed into RNA; reverse transcriptase allows just the opposite to take place. When the reverse transcriptase is attached to the viral RNA is synthesizes many DNA copies of the RNA. Some of these copies are randomly inserted into the host's chromosome's DNA. This modifies and changes the blueprint orders contained in the host cells DNA. The remaining copies of this DNA are transcribed into fresh RNA molecules. Each different gene is translated into a different part of a new retrovirus. A gene called the gag gene is translated into a capsid protein. The pol gene is transcribed into reverse transcriptase and the env gene is translated into the envelope protein. (About Biotech) Not all of the fresh RNA molecules are translated into new molecules; many must be saved to be incorporated into new virus particles. Once assembled, the new particle is ejected from the cytoplasm of the host cell, going on to infect other, new host. Many factors make a retrovirus the perfect tool in up and coming medicine. As long as the virus can be effectively harnessed, it could do work that was before thought impossible. A virus, when engineered correctly, could easily correct many genetic disorders in humans and other mammals. Only one man-made virus is needed to produce large quantities of the new virus or protein that the virus encodes for. It could be injected into a particular mass of host cells and it would spark a chain reaction that would infect and genetically alter all the cells it could reach. With today's technology, custom-built RNA molecules could be inserted into retroviruses and sent easily to a place where they are needed. A virus could be produced to do anything that the "programmer" needed it to. Many helpful retroviruses are made by simply modifying existing viruses to deliver a new genome. Of course, any retroviruses used in medicine are modified so that they will not cause disease. Although they might not cause disease, these retroviruses still may trigger an immune response in the "infected" individual. This brings up another advantage of retroviruses. In a normal immune response, the virus load is lower and eventually extinguished by the immune. However, this cannot happen until the immune system adapts new antibodies to destroy the virus. The advantage with a retrovirus is that although the virus load may be decreased at first, the viral diversity is in turn increased. This leaves the immune system constantly trying to adapt to new viral codes. (Nowak) By the time the immune system has caught up, the virus has completed its job. With all the retroviruses that are known to be harmful, very little is known about the advantages of these mysterious particles, neither living nor dead. Many of the things that do make them dangerous to different organisms, including humans, also make them possibly one of the most valuable resources in the ever-expanding medical field. Bibliography: About Biotech. http://www.gene.com. December 8, 1997 HIV Graphics. http://www1.omi.tulane.edu/departments/pathology/fermin/HIVFIGTable.html. December 4, 1997 Nowak, Martin. "HIV-1 Evolution and disease progression." Science November 8, 1996: 1008-1011. Retropages. http://www-leland.stanford.edu/group/nolan/NL-retropage.html. December 4, 1997 Retroviruses. http:// www.ultranet.com/~jkimball/BiologyPages/R/Retroviruses.html December 7, 1997 Word Count: 1030
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