Trojan horse tmv adenovirus influenza phage basic

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Trojan Horse TMV Adenovirus Influenza Phage
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Basic Viral Replication Different viruses reproduce in a similar way: Nucleic acid is released into a cell. Viral DNA or RNA is then replicated, transcribed, and translated in the cell using the machinery of the cell: i.e., using the cell’s enzymes, ribosomes, tRNAs, ATP, etc. Viruses spontaneously assemble from the parts produced in the invaded cell. New capsid proteins are produced and the new viral genome is packaged within the capsid. Viruses then exit the cell. Hundreds of viruses are produced per cell.
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Bacteriophages (Phages) Phages are viruses that infect bacteria . Remember, Hershey & Chase (1952) used phages to determine that DNA rather than proteins was the genetic material. In their experiments, they radiolabeled phage protein with sulfur ( 35 S) and DNA with phosphate ( 32 P). Phages inject their DNA into bacteria and coopt the bacterial machinery to make more phages. They employ two basic life cycle strategies: The lytic cycle or the lysogenic cycle There are various types of phages: T1, T2, etc., named in order of their discovery.
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The lytic cycle: virulent phages Phages that only uses this strategy are called virulent phages . Viral DNA is injected in a bacterium and the bacterial host’s DNA is degraded (hence destroyed). The virus then uses nucleotides from the degraded bacterial DNA and enzymes in the bacterium to assemble more of its own DNA. This viral DNA then produces all the proteins it needs for more viruses. New viruses are assembled. Lysozymes coded by the viral DNA degrade the cell wall . Once the cell wall is degraded, water rushes into the hypertonic bacterium by osmosis, bursting the bacterium and freeing the new viruses.
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Lysogenic cycle: temperate phages Phages that can use both the lytic and lysogenic cycles are called “temperate phages”. Phage Lambda (λ) is an example. This cycle relies on the Prophage strategy. Instead of breaking down the bacterial DNA, the virus its DNA in the bacterial genome. This incorporated DNA is called a prophage. The viral DNA lies dormant in the bacterial genome – its genes are temporarily turned off by a translated repressor gene. When the bacterium divides, the viral DNA is replicated along with the bacterial genome and distributed in the next generation of bacteria. As we will see, many viruses use this kind of strategy in infecting eukaryotes --e.g., retroviruses like HIV --Herpes mini-chromosomes Sometimes prophage genes control host-bacterial behavior (e.g., causing bacteria to produce toxins of botulism & scarlet fever bacteria) Temperate phages —e.g., the λ phage— can use either the lytic and lysogenic modes of reproduction
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Lysogenic cycle: temperate phages Viral DNA enters the bacterial genome and becomes the prophage. Prophage DNA reproduces along w/ bacterial DNA.
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