And the blue DNA primer is the primer that anneales to the three end of the other DNA molecule as shown in that diagram. And finally in step three, what we have to do is we have to use a special DNA polymerase that is heat resistant and we can obtain this DNA polymerase from prokaryotic cells that live in hot springs. Because in hot springs the temperature is high, it's about in the. So if we use this special heat resistant DNA polymerase, we place it into our mixture and we bump the temperature back up to about 72 degrees Celsius. This is the optimal temperature for this special heat resistant thermosilic DNA polymerase that is called TAC DNA. Now, what the polymerase does, like any polymerase, it uses those primers, it begins at the primers and it moves from the five to the three end to basically synthesize and replicate that DNA molecule.