Loudoun County Public Schools / Overview



VirusesVirology – study of virusesVirologist – scientist that studies virusesIntroduction to Viruses:In 1898, Friedrich Loeffler and Paul Frosch: found evidence that the cause of foot-and-mouth disease in livestock was an infectious particle smaller than any bacteria. This was the first clue to the nature of viruses, genetic entities that lie somewhere in the grey area between living and non-living states. Viruses depend on the host cells that they infect to reproduce. When found outside of host cells, viruses exist as: Protein coat or capsid, sometimes enclosed within a membrane. The capsid encloses either DNA or RNA which codes for the virus elements. In this form outside the cell, the virus is metabolically inert (dormant)Examples of Viruses: Influenza and Tobacco Mosaic VirusDiscovery of VirusesBeijerinck (1897) coined the Latin name "virus"? meaning poison for? the substance infecting tobacco plantsEdward Jenner (1796) developed smallpox vaccine using milder cowpox viruses – the first ever vaccine1900 Walter Reed showed that an agent so small it could pass through a filter, which trapped bacteria, caused the human disease yellow fever1918 a pandemic Spanish flu kills 25 million people, more deaths than caused by the first World WarWendell Stanley (1935) crystallized sap from tobacco leaves infected with Tobacco Mosaic Virus (TMV) & found virus was made of nucleic acid & proteinViruses couldn't be seen until electron microscope invented in the 1930s1950s widespread use of the Salk polio vaccine – killed vaccine1978 last naturally occurring case of smallpox in the world1982 recognition of new virus Human Immunodeficiency Virus (HIV-1)2009 H1N1 Influenza virus – Swine Flu Characteristics of VirusesNot living organisms; NoncellularConsist of a nucleic acid core (DNA or RNA) and a protein coat called the capsidCannot grow or replicate on their own (inactive particles); Can only reproduce inside of a living host cell using its raw materials & enzymesSome can cause disease (smallpox, measles, mononucleosis, influenza, colds, AIDS, Ebola VirusSome may also cause cancers such as leukemiasHighly host specific (only infect certain cells)Viruses are classified into 2 main groups by their nucleic acid --- DNA or RNA VirusesBacteriophage – a virus that infects a specific bacteriaT4 Bacteriophage – virus that attacks the bacteria E. coliLytic & Lysogenic Cycles: 2 ways viruses reproduce in a host cellRetrovirusesContains RNA – RNA enters the cells and makes DNARNA is copied backward – RNA to DNA (usually DNA to RNA)Virus DNA becomes part of host cell’s DNAHides in the cell and copies of the virus can be made at any time.left55728 some cancers and AIDSViroid – infect plants, single stranded RNA molecules that have no capsid – disrupt metabolism and destroy plantsPrion- contain only protein (no DNA or RNA), forms protein clumps in nervous tissue (mad cow disease)Comparing Viruses & Living Cells ................
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