And once that retrovirus infects that whole cell, it injects these two individual RNA molecules into that hostel. Now, because it carries that special enzyme known as reverse transcriptase, this enzyme basically binds onto either of these two viral RNA molecules and it begins to transcribe in the opposite direction to how it normally takes in our own cells. So instead of going from DNA to RNA, this goes from RNA to DNA in reverse. And so eventually, we synthesize these complementary viral DNA molecules and once they separate, once they anneal, actually right, so once these two blue strands actually separate, these two blue strands, because they're complementary with respect to one another, they can basically anneal. And to anneal means to combine to form that double helix structure. And once we form the viral double stranded DNA molecule, that DNA molecule is brought into the nucleus of the cell.