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Lysogenic Cycle of a Virus: Definition & Steps

Instructor: Shannon Compton

Shannon teaches Microbiology and has a Master's and a PhD in Biomedical Science. She also researches cancer and neurodegenerative diseases.

Once a virus infects one of your cells it begins to replicate. Some viruses make hundreds of copies of themselves and then escape their host. Lysogenic viruses choose a different path. They can actually insert their genetic material into your DNA.

Definition

In the viral life cycle there are two ways to reproduce. One results in thousands to millions of copies of virus (virions) being released in a few hours. This method results in the death of the host cell because the virions cause the host to lyse. This is the lytic cycle. The other replication method results in only a few virions being released at a time. The advantage is that the virus can survive and replicate inside a host for many years because there is no host cell lysis. This is the lysogenic cycle.

The main difference between the lytic and the lysogenic cycles is the location of the viral genome. In the lytic cycle, the genome remains in the cytoplasm. In the lysogenic cycle the genome enters the nucleus and inserts into the host genome. In both cases the virus is dependent on the host replication machinery to make viral proteins and genome (new virions).

The lysogenic and lytic cycle
Image of the lysogenic and lytic cycle

The Lysogenic Viral Life Cycle Step One: Exposure

For a virus to reproduce it must infect a host cell. To do this it must first come in contact with the host organism and enter the host organism. Exposure of the host to the virus is the first step in the viral life cycle. Viruses can enter a host in several ways. For example, through a cut in the skin, a mosquito bite (inoculation), or by direct contact with mucus membranes.

The Lysogenic Viral Life Cycle Step Two: Viral Entry

Once a virus has gained entry it can access target host cells. Viral proteins interact with host surface proteins during entry. The first step is attachment, which is when the viral particle physically attaches to the host. Next, the virus creates a hole in the host membrane. Finally, the virus injects its genome into the host.

At this point the lysogenic and lytic cycles diverge. In the lytic cycle the virus rapidly takes over the host machinery and forces it to make millions of new viruses. In the lysogenic cycle the virus genome enters the host nucleus and becomes part of the host genome.

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