So these plasmids can essentially be engineered in a laboratory and we can insert different types of recombinant DNA molecules into these plasmids. And then we can take the plasma and place it into the cell. And when the cell replicates, it will replicate that plasma. And by that method, we can essentially produce many copies of that DNA of interest, the recombinant DNA molecule. Now, in biochemistry, there are two types of plasmids that we commonly use. So we use PBR three, two, two, and we also use PUC 18.