And inside the nucleus, a second type of special protein enzyme known as integrase, basically cuts the host DNA molecules. So the green DNA is the host DNA, it cuts a section of that DNA molecule, it opens it up, and this double stranded DNA molecule that came from the virus basically injects itself integrates with that host DNA. And this is how the majority of retroviruses actually work. So we conclude that although in all living cells, DNA molecules are the carrier of the genetic information, in some living organisms we have linear DNA molecules and in others we have circular. Now, in any cell, we're never going to find these forms. Instead, they're going to be super coiled into these compact structures.