113lecture1806 - BIOLOGY 113 - MICROBIOLOGY Lecture 18:...

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BIOLOGY 113 - MICROBIOLOGY Lecture 18: Viruses - Viral multiplication strategies The genome of a virus encodes relatively few proteins - Among these, of course, are the proteins that make up the virion capsid - The genome also encodes a number of viral enzymes, that are not usually part of the virion = Most of these are concerned with replication and processing of the viral genome = Some viral enzymes also play a role in assembly of the virion - Even with its own enzymes, a virus is entirely dependent on the host cell for protein synthesis The best understood viral life cycles are those of the T-even bacteriophages; these serve as good examples for the events of viral multiplication in bacteriophages, plant viruses and animal viruses (Tortora et al., Figure 13.10) - The capsids of T-even bacteriophages are complex, and the genome has enough DNA for over 100 genes (this is a large number of genes for a virus) - The multiplication cycle of a T-even phage begins with attachment or adsorption of the phage virion to an Escherichia coli host cell; weak bonds (e.g., hydrogen bonds) are formed between virion proteins and receptor sites on the surface of the E. coli cell - Following successful attachment, penetration of the viral genome occurs = A lysozyme (cell-wall lytic enzyme) in the phage "tail" catalyzes hydrolysis of a portion of the cell's peptidoglycan = This creates a hole through the "core" of the tail is driven through the cell wall by contraction of the tail "sheath" = The DNA genome passes through the tail, and across the plasmid membrane into the E. coli cytoplasm = The virion capsid remains outside of the cell; only the genome enters the cytoplasm - Once the genome is inside of the cell, several of its genes are expressed that lead to organized expression of additional genes and biosynthesis of viral components = First the genome itself is replicated, which provides multiple copies of phage genes
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This note was uploaded on 11/24/2011 for the course BIO 113 taught by Professor Staff during the Fall '09 term at Rutgers.

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113lecture1806 - BIOLOGY 113 - MICROBIOLOGY Lecture 18:...

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