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Provirus: Definition & Concept

Instructor: Julie Zundel

Julie has taught high school Zoology, Biology, Physical Science and Chem Tech. She has a Bachelor of Science in Biology and a Master of Education.

Even if you didn't know it, you have probably had a virus (or two) within the last three months. This lesson will focus on the provirus, or when viral genetic material is incorporated into your DNA. It will also explain how proviruses are linked to cancer.

Definition of a Provirus

As you sit on the couch, drinking your coffee or watching TV, you are under attack. A tiny monster has forced its way into your cells and is inserting its genetic material into your genetic material. It will sit and wait until the moment is right, and then it will hold your cells hostage, forcing them to make more and more and more monsters. Eventually these tiny monsters will burst from your cells and infect new cells. This doesn't really happen, you may say to yourself... but it does and has maybe even happened to you!

The story you just heard was an overview of the lysogenic and lytic cycles, which are ways viruses can attack your cells. The monsters in the story are actually viruses, or tiny infectious agents that can only reproduce inside a host. The provirus is when the virus integrates its genetic material, DNA or RNA, into the host cell's DNA.

Note: Many viruses use RNA instead of DNA. RNA is genetic material, like DNA, with a few differences. We'll just use DNA here for simplicity, but keep in mind that it could be DNA or RNA.

Viral Cycles and the Provirus

In order to understand the provirus, let's quickly go through the steps of the lysogenic cycle:

1. A virus enters your body and attaches to a cell.

2. The virus inserts its DNA into your cell. Your DNA is the black squiggle line and the viral DNA is colored red.

3. The viral DNA is incorporates into your cell's DNA, and this is a provirus. Note: in bacteria it is called a prophage.

4. When your cell divides, the DNA of the cell and the virus is replicated.

Steps 3 and 4. Notice how the viral DNA, shown as a perpendicular red line. is incorporated into the host
provirus

Although your body is making more viruses, you do not feel sick during this cycle.

Eventually the virus will enter the lytic cycle, where the viral DNA leaves the host's DNA and hijacks the cell, forcing it to make more viruses. Finally, the new viruses burst from the cell and infect new cells. During the lytic cycle the host feels sick. Scientists believe that the lytic cycle is triggered when the host is sick, stressed out or rundown and the immune system isn't at 100%.

Overview of the lysogenic and lytic cycles
viral cycles

Example Viruses and Cancer Risks

There are many viruses that make a provirus, including:

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