Study Notes Final - Study Notes Micro Final Chapter 5 -...

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Study Notes – Micro – Final Chapter 5 - Viruses – Probably the most ubiquitous biological entities on the planet, existing in truly astronomical numbers. For example, its been estimated that there are 10^30 bacteria and 10^31 bacteriophages. Viruses are acellular, meaning that they are not cells, but rather they are parasitic and can’t replicate independently of a host cell. o The basic structure of a bacterial virus is a genome (RNA or DNA) surrounded by a protein coat, called a capsid. The combination is known as a nucleocapsid. A bacterial virus is known as a virion or a bacteriophage, often shortened to phage. Morphologically there are many sizes and shapes to virions. - Major Characteristics of Viruses o Acellular o Depend on a host for replication (like plasmids) o Contain either RNA or DNA (in their genome) but not both o Have no metabolism o They can exist in an extracellular or intracellular state So in this respect they differ from plasmids, which aren’t found in an extracellular state Like plasmids, in an intracellular state a virus could replicate independently of the host’s chromosome, or in some case integrate into the chromosome of the host. Only some viruses have this capability, and they are referred to as Temperate Viruses o Viruses have a genome and can mutate Consequently like all cells, they can evolve and become resistance to certain medicines - Types of Capsid – Is a major feature of the structure of a virion and there are two major types o The Helical Capsid – this is found in the tabacco masoic virus This is the first virus discovered An important aspect of the structure of the helical capsid is that it is composed of repeating units of the same protein. This protein is referred to as the protomer. The protomer bond together spontaneously to form the capsid, and this type of process, which is important in biology is called self assembly Enzymes are not needed for this process o The Icosahedral Capsid – This is the second major capsid structure Consists of either a Penton (5) or a Hexon (6) protomers in a pattern
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Whats amazing about this capsid structure is that it has been shown to be the most efficient structure for enclosing space Bulky balls in organic chemistry? – soccer ball structure – dome o Nucleo Capsid – these are enveloped viruses – also eukaryotic viruses The nucleocapsid is surrounded by a lipid bilayer that is acquired from a former host cell Viral proteins called spikes or peplomers protrude through the bilayer Examples include influenza virus Two of these spikes are neuraminidase and hemagglutinin - Forms of Nucleic Acids in Viruses o DNA – probably most viruses are DNA viruses and the DNA is usually in double stranded form. There have been cases and exceptions when the DNA is in a single stranded form o RNA – Most RNA viruses have a single strand of RNA. An exception is where you will find an RNA strand that is double stranded
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This note was uploaded on 02/21/2012 for the course BIOLOGY 2280 taught by Professor Irvinn.hirshfield during the Fall '11 term at St. Johns Duplicate.

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Study Notes Final - Study Notes Micro Final Chapter 5 -...

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