dCTP, and dTTP as substrates, while RNA synthesis requires ATP, GTP, CTP, and UTP.

Nucleic acid synthesis is catalyzed by either DNA polymerase or RNA polymerase for DNA and RNA synthesis respectively. These enzymes covalently link the free -OH group on the 3' carbon of a growing chain of nucleotides to the ?-phosphate on the 5' carbon of the next (d)NTP, releasing the ?- and ?-phosphate