Lysogenic cycle
Virology · Microbiology · Molecular Biology
Say it: ly-suh-JEN-ik SY-kul
The lysogenic cycle is a phage life cycle in which viral DNA joins the host bacterium's chromosome and is copied with it instead of killing the cell.
Also: lysogeny, lysogenic pathway
Definition
What is the lysogenic cycle?
The lysogenic cycle is one of the two ways a bacteriophage, a virus that infects bacteria, can reproduce. After the phage attaches and injects its genome, the viral DNA does not take over the cell straight away. Instead it joins the bacterial chromosome, where it is called a prophage, and the infected bacterium is called a lysogen. Phages that can do this, such as lambda phage in Escherichia coli, are known as temperate phages.
While it stays integrated, the prophage is mostly silent and is copied every time the bacterium divides, so every daughter cell inherits it. Stress such as ultraviolet light or harmful chemicals can trigger induction: the prophage cuts itself out of the chromosome and switches to the lytic cycle, making new viruses and bursting the cell. Prophage genes can also change the host, a process called lysogenic conversion. The gene for cholera toxin, for example, arrives in Vibrio cholerae on a phage, and strains without it are far less harmful.
Students meet the term in microbiology and virology, usually in a side-by-side comparison with the lytic cycle. A related idea applies to some animal viruses: HIV inserts a DNA copy of its genome into the host chromosome as a provirus, and the chickenpox virus can lie dormant in nerve cells for years.
Word parts
Where does the term “lysogenic cycle” come from?
- lyso-
- loosening, dissolvingGreek lysis
- -genic
- producing, giving rise toGreek -genēs
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Terms that go with it
- Lytic cycleThe lytic cycle is a viral life cycle in which a phage takes over a bacterial cell, makes many copies of itself, then bursts the cell to release them.
- BacteriophageA bacteriophage, or phage, is a virus that infects bacteria, injecting its genome and using the host cell's machinery to make new phages.
- VirusA virus is a tiny infectious particle of DNA or RNA inside a protein coat that can multiply only by taking over the machinery of a living host cell.
- RetrovirusA retrovirus is an RNA virus that copies its genome into DNA with reverse transcriptase and inserts that DNA into the host cell's chromosomes.
- BacteriumA bacterium is a single-celled prokaryote with no nucleus, found in almost every habitat on Earth, including in and on the human body.
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