There are several human virii that have been known to trigger cancer-why is this?
I thought viruses merely injected themselves into cell, and cause the cell to duplicate the virus-why does the virus wind up triggering the abnormal growth of the host cells(cancer)?
Is there a simple explanation for this?
Disclaimer: I am not a virologist. This is my layman’s understanding.
Most of the DNA in your cell is inactive at any one time. When a retrovirus infects a cell, it copies itself into the cell’s DNA. In order to reproduce, the virus needs that section of DNA to be active. Some viruses carry promoter sequences, which are sections of DNA that cause the DNA code following the promoter sequence to become active, in order to trigger their DNA to become active and create new viruses. This can cause the normal cellular DNA that happens to be following where the virus has randomly inserted itself to become active. If the virus randomly inserted itself in a position in the cellular DNA just before the DNA that activates to cause the cell to duplicate itself, then in the process of inserting itself and activating its own DNA the virus can also trigger the cell to begin uncontrollably duplicating itself. Hence, cancer.
A virus that gets copied into your DNA can mess with your cells’ growth by:
Disrupting genes that control cell death.
Disrupting genes that control cell growth.
It’s a little more complicated than that (ok, maybe a lot more complicated than that), but essentially a virus just shoves its way in there and can mess up a gene’s function (or mess up its promoter region). Any gene that controls cell growth and death is called an oncogene because if you mess with it, you can get uncontrolled growth and tumors.
Some viruses actually carry their own oncogenes, so it doesn’t matter where in the DNA they land - they can start switching on cell proliferation without your genes’ help.
There is no such thing as virii. There are, howver, viruses.