Without all of these elements, daisy chaining of the nucleotides would not be possible. Drugs can be designed to take advantage of these processes. If DNA groups are cleaved, thymidine kinases can help add a new phosphate group to the hydroxyl group. Herpes Simplex Virus is a DNA virus that wants to replicate its genome quickly. The HSV brings along its own thymidine kinase to replicate itself on salvaged pathways of DNA synthesis.
Thymidine kinase is encoded by the virus as well as our own bodies.
Drugs can be created to target the thymidine kinase of the virus. Without the extra hydroxyl group, chaining cannot continue. HSV is very effective at adding phosphates with its own thymidine kinase but the chain stops because of lack of the hydroxyl group. Healthy cells can ignore acyclovir, but infected cells activate acyclovir. Pathways are worked on by enzyme catalysts with great specificity.