The polymerase begins DNA synthesis on the primers and elongates in a five to three direction on both ends. And this is shown in the following diagram. So the DNA polymerase attaches onto this five prime primer and it moves along this direction, synthesizing the complementary strand to this DNA molecule. And likewise, another DNA polymerase attaches onto this side and moves in this direction, synthesizing the complementary strand to this DNA strand here. And so after one cycle of PCR, we have two copies of that DNA molecule. Now, the great thing about PCR is we don't have to do anything else to repeat the cycle.