In - • Capsid a protein capsid divided into a head that...

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In lytic cycle: phage converts the metabolism of the infected cell to produce phage progeny. Phage that can only undergo lytic cycle is called virulent . Some phages can additionally undergo lysogenic cycle . These phages are called temperate . In lysogenic cycle phage DNA is usually inserted into the host chromosome where it is silent (no phage progeny produced) and but is passed on from cell generation to cell generation. A phage that is integrated into the bacterial chromosome is called a prophage . Under appropriate conditions, DNA integration can be reversed and the lytic cycle is initiated. Bacteriophage lambda consists of: Genome: a linear fragment of double-stranded DNA
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Unformatted text preview: • Capsid: a protein capsid divided into a head that contains the DNA and a tail that plays a role in attaching to the specific host bacterium and injecting the DNA. Bacteriophage lambda specifically infects E. coli . After infection, the linear lambda DNA is converted to a circular, supercoiled form and transcription of lambda genes starts . At this point, decision is made on which life cycle to follow (see Fig. 5.37). What decides? Seems to be the concentration of an activator protein transcribed from lambda DNA this activator is designated cII: high concentration of cII ---- lysogenic cycle favored low concentration of cII ---- lytic cycle favored...
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