Lysogenic Cycle: Overview & Steps

Lytic Cycle vs. Lysogenic Cycle

Viruses can cycle through the lytic cycle and lysogenic cycle depending on several factors. Both cycles have some similarities, but they are quite different. One major difference between the lytic and lysogenic cycles is the location of the viral genome. During the lytic cycle, the genome of the virus has already been incorporated into the host cell's genome, and the cycle continues to produce proteins for the virus's progeny, or future generations. Conversely, during the lysogenic cycle, the genome of the virus may not have been incorporated yet into the host cell's genome. It is the main function of the lysogenic cycle to do this, and it may take until the end of the cycle for the virus to inject its genome into the host cell's genome.

Another difference between the two cycles is the effect on the host cell. During the lytic cycle, the host cells may be dying as a result of new viruses being released. During the lysogenic cycle, the virus attempts to keep the host cell alive so that it can inject its genetic information into it to allow it to make new viruses when the host cell divides.

This is a diagram showing when a Lamba phage, a type of virus infecting a bacteria, may be in the lytic cycle or lysogenic cycle

Lesson Summary

The lysogenic cycle is a viral reproductive stage where the virus's DNA is replicated using the host cell's DNA. Most cells can go through this cycle, but it is often found in viruses that infect bacteria. When the lysogenic cell happens in a virus that infects bacteria, it is called a bacteriophage. This stage has several steps, including the following:

1. The genome of the virus enters the host cell. This step includes exposure of the host organism to the virus, and the cycle would not begin otherwise.
2. The proteins of the host cell that are responsible for replicating the DNA normally read and then replicate the viral DNA. The virus has already attached to the host, created a hole in its cell membrane, and injected its DNA by the time this step is completed.
3. Viral DNA uses the host's machinery to replicate. If this does not occur, it will switch over to the lytic cycle. While it remains in the lysogenic cycle, usually one, or a couple, copies of the DNA are in existence in the host cell. Additionally, DNA only gets reproduced when the host is reproducing its own DNA.
4. The lysogenic cycle continues or the virus can switch to the lytic cycle to produce more DNA and capsids.
5. Finally, capsids are released and are then able to infect a new bacteria. The lysogenic cycle can re-start or, if the host is in danger of dying, the virus may switch over to the lytic cycle in an effort to keep the host cell alive.

Viruses really depend on the host cell's machinery for replication. One primary difference between the two virus cycles, the lytic and lysogenic cycles, is the location of the genome during the cycle. Viruses can go through budding, which is the usual method of virion release in a lysogenized host.