Lesson Plan - Get It!
Virulent viruses usually cause many symptoms in the host, because as the host cells are destroyed, the host's immune system kicks into gear to fight back when the cells are destroyed. Viruses that replicate using the lysogenic cycle can remain dormant for years before becoming active and going on the attack. Can you think of any viruses that behave in this manner?
There are two types of viral reproduction cycles.
Before you continue with this lesson, if you have not completed the previous three Related Lessons in this Viruses and Bacteria series, find them in the right-hand sidebar.
Viruses reproduce using the lytic and lysogenic cycles. In this lesson, you will learn about the lysogenic cycle. This cycle is also referred to as the inactive cycle. Viruses that reproduce using both the lytic and lysogenic cycles are called temperate viruses.
During the lysogenic cycle, the virus injects its prophage into the host cell and embeds its DNA / RNA into the host cell's DNA. The prophage is the genetic material of a bacteriophage embedded into the DNA of a bacterium, and is able to produce bacteriophages if activated in the lytic cycle. Temperate viruses can switch from one cycle to another.
In the lytic cycle, the virus only replicates itself and destroys the cell when the new bacteriophages are released. The difference in the lysogenic cycle is that the virus DOES NOT destroy the cell. It actually becomes part of the host cell's DNA. When the host cell reproduces, it also reproduces the viral DNA that is now embedded in it. This cycle results in a higher quantity of viruses being reproduced over time, because every time the bacteria reproduces, it also reproduces the virus' DNA / RNA.
Image by Sseifert242, via Wikimedia Commons, is licensed under the CC BY-SA 4.0 license.
This virus can lay dormant for many years before becoming active and switching to the lytic cycle. With temperate viruses, the question isn't, "What makes them go dormant?"; the question is, "What makes them go active?". When ideal conditions are present, the virus will switch from the lysogenic cycle to the lytic cycle. What constitutes ideal conditions varies from virus to virus.
Watch Lysogenic Cycle by Beverly Biology (below) and fill out the Lesson Four Viral Production Lysogenetic Cycle section on Page Seven in the Viruses and Bacteria Unit Workbook found in Downloadable Resources in the right-hand sidebar (You should have this from the previous lessons). Pause the video whenever necessary to write down information:
Discuss with your teacher or parent what happens in each step of the cycle. Which steps of the lysogenic cycle are the same in the lytic cycle?
Temperate viruses can switch between the two cycles; however, as long as they remain in the lysogenic cycle, the host usually will not have any symptoms. The virus only integrates itself into the host cell's DNA, and every time the bacteria reproduces, so does the viral DNA. Pretty clever, yes?
Continue on to the Got It? section to continue to fill out your workbook with new information and artwork!