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Overview of the Lysogenic Cycle

Bryan McMahon, Shannon Compton
  • Author
    Bryan McMahon

    Bryan is a veteran high school special education science teacher with over 15 years of experience. Bryan holds a Master's degree in Curriculum, Instruction and Assessment, along with his dual undergrad degree in Biology and Special Education. Most recently, Bryan has been creating content and writing curriculum in the educational technology field.

  • Instructor
    Shannon Compton

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

Learn what the lysogenic cycle is. Explore the lysogenic cycle steps, what a lysogenic infection is, and the difference between the lytic and lysogenic cycle. Updated: 04/08/2022

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What is the Lysogenic Cycle?

Viruses are all around us and come in many different varieties. Viruses are often considered non-living due to their need for a host in order to replicate. As part of their replication and development, viruses go through two distinct cycles, known as the lysogenic and lytic cycles. The lysogenic cycle definition is a viral reproductive stage where the virus's DNA is being replicated using the host cell's DNA. During lysogenic infection, the virus uses the host to help copy its DNA or genetic information, but it is not producing any proteins. The virus truly depends on the host cell's machinery for its reproduction and existence at that point.

The lysogenic cycle is most common in prokaryotic cells, which include mostly bacteria. It can, however, occur in eukaryotic cells, which include animals and plants alike. Oftentimes, the lysogenic cell happens in viruses that infect bacteria, also known as bacteriophages. When a virus attacks a host cell, there are about five distinct steps in the lysogenic infection or cycle. After a virus has infected a bacteria, and the stages of the lysogenic cycle are completed, the lysogenized host cell can either enter the lytic cycle where more virus particles and proteins are made or remain in the lysogenic cycle where the virus can be latent, or hidden, for a period of time. Normally, the method of virion release in a lysogenized host is called budding.

Lysogenic Cycle Steps

The steps of the lysogenic cycle are part of the virus's reproductive cycle and depend solely on the virus's ability to find a host. The steps are as follows:

  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. In order to continue its existence, viral DNA uses the host 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, of 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. At this point of the lysogenic cycle, the virus would need to switch to the lytic cycle to produce more DNA and capsids, which are protein coats. Otherwise, the virus does not do these functions in the lysogenic cycle.
  5. Finally, capsids are released and are then able to infect a new bacteria. The lysogenic cycle can re-start from the beginning. 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.

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  • 0:00 What Is the Lysogenic Cycle?
  • 0:52 Why Do Viruses Invade Cells?
  • 1:49 Exposure
  • 2:14 Attachment and Entry
  • 3:09 Replication and Release
  • 4:33 Lesson Summary
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What is a Virus?

A virus is a particle that invades and replicates using a host cell by inserting its genetic information into the host's genetic information. Scientists often argue that viruses are not technically living due to the fact that they cannot reproduce unless they have invaded a host cell. The main components of a virus are genetic information, either DNA or RNA, and a protein coat. The protein coat is what makes each virus unique and helps scientists to identify viruses and classify them into similar families.


The protein coat of the tobacco mosaic virus is shown here

A scientific drawing of a virus, showing its protein structure


Another way that viruses are classified is by the type of organism that they infect. Viruses can be specific to infecting animals, bacteria or plants, like the tobacco mosaic virus shown here. Finally, viruses can be classified by their type of genetic information. This would include DNA and a few types of RNA.

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Frequently Asked Questions

What are the 5 stages of the lytic cycle?

The lytic cycle has five stages:

1. Attachment to the host

2. Recognizing host cell membrane

3. Entry into the host cell

4. Host cell replication, including viral genome

5. Development of new virus

What is the difference between lytic and lysogenic cycle?

The primary difference between these two cycles is the location of the viruses genome. During the lytic cycle, the genome is incorporated in the host cells genome, while the virus' genome is not yet incorporated most likely during the lysogenic cell.

What are the steps of the lysogenic cycle of some viruses?

There are five main stages of the lysogenic cycle. There are as follows:

  1. The genome of the virus enters the host cell.
  2. Proteins of the host cell replicate the DNA normally read and then replicate the viral DNA and then virus creates a hole in its cell membrane and injected its DNA by the time this step is completed.
  3. Viral DNA uses the host machinery to replicate. Additionally, DNA only gets reproduced when the host is reproducing their own DNA.
  4. At this point, the lysogenic cycle continues or the virus can switch to the lytic cycle to produce more DNA and capsids.
  5. Finally, capsids are able to infect a new host cell after they are released.

How many stages are there in the lysogenic cycle?

There are five main stages of the lysogenic cycle. There are as follows:

  1. The genome of the virus enters the host cell.
  2. The proteins of the host cell that are responsible for replicating the DNA normally read and then replicate the viral DNA.
  3. Viral DNA uses the host machinery to replicate.
  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.

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