So the molecule is this molecule here. It's called two prime, three prime dioxy nucleuside triphosphate or simply Ddntp. Now, this molecule is almost identical to a normal deoxy nucleuside triphosphate. The only difference is the sugar component contains a three prime carbon that does not contain a hydroxyl group. So remember, in a normal deoxy nucleus triphosphate, the presence of the hydroxyl group on the three prime carbon allows DNA polymerase to actually form a phosphodiastor bond with the next nucleotide in line. So in the process of DNA synthesis, when we're replicating a DNA strand, the DNA polymerase needs this hydroxyl group to be present on the three prime carbon to actually form the phosphodiaester bond.