BY123 Final Exam Notes - Chapter 19 section 1 and 2 Viruses...

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Chapter 19 section 1 and 2 - Viruses are basically genes packaged in protein coats - They lack the structures and metabolic machinery found in cells - Because scientists saw a parallel between bacteria and viruses, viruses are labeled as the simplest of living forms! - They cannot reproduce or carry out metabolic activities outside of a host cell - Most biologists say that viruses are not alive and they lead a “borrowed life” The Discovery of Viruses - Adolf Mayer discovered that he could spread a tobacco mosaic disease from plant to plant by rubbing infected sap onto healthy plants - Mayer suggested that the disease was caused by unusually small bacteria that were invisible under a microscope - Dimitri Ivanowsky believed it was bacteria that infected the tobacco plants and did a filtration technique, but the plants were still infected - Martinus Beijerinck then did experiments showing that the infectious agent in the filtered sap could reproduce - The pathogen only reproduced within the host it infected - Beijerinck showed that the pathogen could not be cultivated on petri dishes (like bacteria could) - Beijerinck is the first scientist to voice the concept of a virus - Wendell Stanley crystallized the infectious particle, now known as tobacco mosaic virus The Structure of Viruses - The tiniest viruses are smaller than a ribosome; the largest is barely visible by a light microscope - Viruses genes can be double stranded DNA, singled stranded DNA, double stranded RNA, or single stranded RNA - A virus is called a DNA virus or an RNA virus according to the kind of nucleic acid that makes up its genome - The genome is organized as a single linear or circular molecule of nucleic acid - Capsid: the protein shell inclosing the viral genome - The capsid can be rod shaped, polyhedral, or more complex shape - Capsids are built from capsomeres (protein subunits); the number of different kinds of proteins in a capsid is usually small - Rod shaped – helical virus; icosahedron shape – icosahedral virus - Some viruses have accessory structures that help them infect their hosts - Like some viruses have viral envelopes (that surround capsid) that are derived from the membranes of the host cell; they contain host cell phospholipids and membrane proteins and proteins and glycoproteins of viral origin - Bacteriophages or phages are viruses that infect bacteria, and they’re usually most complex capsids Virus Reproduction - Viruses can only reproduce within a host cell! - Each type of virus can infect cells of only a limited variety of hosts. This is called the host range of the virus
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- Viruses identify host cells by a lock and key fit between viral surface proteins and specific receptor molecules on the outside of cells - A viral infection begins when a virus binds to a host cell and the viral genome makes its way inside - Entry can be done in different ways; some viruses use their tail to inject DNA, some viruses are taken up by endocytosis, or some by fusion of the viral envelope with the plasma membrane
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This note was uploaded on 06/08/2011 for the course BIOLOGY 123 taught by Professor Fischer during the Fall '11 term at University of Alabama at Birmingham.

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BY123 Final Exam Notes - Chapter 19 section 1 and 2 Viruses...

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