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The lysogenic cycle is complementary to the lytic cycle for viral entry and reproduction within cells. While the lytic cycle is common to both animal viruses and bacterial phages, the lysogenic cycle is more commonly found in animal viruses.
The following are the steps of the lysogenic cycle:
- 1) Viral genome enters cell
- 2) Viral genome integrates into host cell genome
- 3) Host cell DNA polymerase copies viral chromosomes
- 4) Cell divides and virus chromosomes are transmitted to cell's daughter cells
- 5) At any moment when the virus is "triggered", the viral genome detaches from the host cell's DNA and enters stage 2 of the lytic cycle. While it is unclear as of yet what exactly constitutes a "trigger" that activates the viral DNA from the latent stage entered in Step 4, common symptoms that appear to "trigger" the viral DNA are hormones, high stress levels (adrenaline), and free energy within the infected cell.
An example of a virus that enter the lysogenic cycle is herpes, which first enters the lytic cycle after infecting a human, then the lysogenic cycle before travelling to the nervous system where it resides in the nerve fibers as an episomal element. After a long period of time (months to years) in a latent stage, the herpes virus is often reactivated to the lytic stage during which it causes severe nervous system damage.
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