BIOL1020 Study Guide - Final Guide: Lysogenic Cycle, Prophage, Molecular Switch
Lytic and lysogenic cycles!
Bacteriophages can infect a bacterial cell and then enter two different life cycles
The chromosome entering the host is the same but what regulates which cycle it goes into
is the regulatory genes of the chromosome
Lytic cycle
•the bacteriophage makes many more copies of itself
•And then kills the bacterial cell through lysis
•Phages that only go through the lytic cycle are called virilant
Lysogenic cycle
•the DNA of the bacteriophage (the prophage) becomes incorporated into the bacterial
chromosome at a very specific site.
•The prophage is replicated along with the host chromosome
•Temperate phage - can go through both cycles
•Prophage is passed from generation to generation in bacteria without ever killing the cell
•However, one day, something can trigger the virus to enter lytic phase again and the
bacteria can die.
•Possible stimulants to return to the lytic cycle: UV rays, chemicals
•To keep the phage in Lysogenic cycle, the phase has a small number of proteins which
are transcriptional regulators. They switch of transcription for the rest of the gene.
•In order to enter lytic cycle, this repression has to be reversed. This process is the
molecular switch.
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