viruses(bio) - Viruses and Virus Genetics Viruses are...

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Viruses and Virus Genetics Viruses are unique substances. They are composed of a genetic molecule surrounded by a protein coating, and sometimes a membranous "envelope". Viruses cannot replicate themselves, but when they enter a host cell, they are capable of turning the host genetic molecules into virus making "machines". Adolf Meyer first detected what was ultimately identified as a virus in 1883 when he was studying a disease of tobacco that caused the plants to be stunted and their leaves to have a mottled or mosaic appearance. The disease could be transmitted by a sap extract, but whatever was in the sap extract that caused the disease was too small to be seen in a microscope. It was first thought that the organism was either a bacterium so tiny that it passed through bacterial-trapping filters or else it was a toxin produced by the bacterium. Since it was demonstrated that the substance could reproduce, it could not be a toxin. However, the infectious agent could not reproduce outside of the tobacco plant on any known growth medium, nor did it succumb to toxins that normally destroyed bacteria. Beijerinck postulated that the substance was a particle smaller and simpler than bacteria. Stanley confirmed Beijerinck's hypothesis when he crystallized the substance in 1935. The infectious agent in the sap extract was ultimately called the Tobacco Mosaic Virus (proving that biologists sometimes give things sensible names). Even so, the first virus particle was not seen until electron microscopes. Viruses may be as small as 20 nm, which is smaller than a ribosome. Eukaryotic cells are about 1000 times bigger than a typical virus. Virus Structure – Genetic Molecule and Protein Coating Genetic Molecule Virus genetic material is more variable than that of living organisms. The virus genetic molecule has from 4 to a few hundred genes and is either a single linear nucleic acid or a circular nucleic acid molecule. It can be: Double stranded DNA Single stranded DNA Double stranded RNA Single stranded RN A
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Protein Coating The genetic molecule of the virus is enclosed in a protein shell or coating called a capsid . The capsid, composed of protein molecules called capsomeres , can be: Helical (forming a rod-shaped virus) Polyhedral Complex With a tail With a membranous coating or viral envelope that is derived from host cell membrane with viral proteins and glycoproteins added. Such viral envelopes may enclose a number of individual virus particles. The human flu virus is an enveloped virus that has 8 RNA molecules, each with its own capsids. Viruses that invade bacteria have historically been called bacteriophages or phages , and are the most studied. The bacterial host most frequently studied has been Escherichia coli ( E. coli ) and the first phages studied with E. coli were simply numbered Type 1 -> Type 7 (or T1 -> T7).
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viruses(bio) - Viruses and Virus Genetics Viruses are...

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