14.+Animal+Viruses - Animal Viruses Viruses(L= poison are...

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Viruses Page 1 Animal Viruses Viruses (L= poison) are Obligatory Intracellular Parasites. They are completely dependent on Host Cell Genetic and Biochemical Mechanisms for the Synthesis of new Virus Particles. Viruses are Biological Entities consisting of: • Genome The Virus Genome is composed of either DNA or RNA. • Capsid (L= box). The Capsid is a protective Covering composed of Protein. • Envelope (Some Viruses) The Envelope is a Host-derived Lipid Membrane. Genome • The Genome of a DNA Virus can be -- - Double-Stranded DNA (dsDNA) - Single-Stranded DNA (ssDNA) Single Stranded DNA can be -- • Positive Sense (or Plus Sense) - The DNA Sequence Equivalent of mRNA • Negative Sense (or Minus Sense) - Template for mRNA • The Genome of an RNA Virus can be -- - Double Stranded RNA (dsRNA) - Single Stranded RNA (ssRNA) Single Stranded RNA can be -- • Positive Sense (or Plus Sense) - Analogous to mRNA (and frequently serves as mRNA) • Negative Sense (or Minus Sense) - Analogous to a Template for mRNA Remember, mRNA is Positive Sense. The Template for mRNA -- whether it’s a DNA Template or an RNA Template -- is Negative Sense.
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Viruses Page 2 Capsid (L= box) Capsids are composed of Subunits called Capsomeres (L= box units) • Capsomeres are sometimes (but not always) identical Subunits Back in the early 1950s Virologists calculated that a Virus could not possibly encode for all the Proteins present in the Capsid unless these Proteins were all Identical Subunits. This way the Virus only has to encode one Protein Subunit and then instruct the Host Cell to make lots of Copies of these Protein Subunits. Capsid Proteins are sort of like Lego™ Blocks. By the mid-1950s Virologists began to realize that Capsid Assembly was an enormously intriguing Process. Studies with Tobacco Mosaic Virus in particular indicated that Virus Capsids could be made to assemble and disassemble in vitro by altering Factors like pH. It was proposed that Viruses are capable of a Process termed Self-Assembly. Since that Time, numerous Biological Structures – including Bacteria Flagella -- have been shown to Self-Assemble, a Crystallization-like Process where the intact Capsid represents a lower Energy State than the individual Capsomers. Capsids are usually capable of Self-Assembly • Self-Assembly resembles Crystallization - The intact Capsid represents a lower Energy State than the Collection of individual Capsomeres • Self-Assembly is limited to regular Geometric Solids - Helix A “Spiral” Staircase is Helix. - Icosahedron A Soccer Ball is sorta-kinda like an Icosahedron (most Soccer Balls are made of 12 Black Pentagons and 20 White Hexagons). • So most Viruses Capsids are either a Helix or an Icosahedron (G= 20 heads) - Or Combinations thereof The Greeks were fascinated by the four Geometric Solids (“Platonic Solids”). These were: Platonic Solid Composition Tetrahedron 4 Triangles Cube 6 Squares Octahedron 8 Triangles Icosahedron
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This note was uploaded on 08/23/2011 for the course MIC 101 taught by Professor Mann during the Spring '09 term at UC Davis.

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14.+Animal+Viruses - Animal Viruses Viruses(L= poison are...

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