Practice question

Incorporation of dNTP involves formation of phosphodiester bond between 3' OH of primer and α-phosphate of nucleotide, releasing inorganic pyrophosphate. Under cellular conditions, subsequent hydrolysis of pyrophosphate into two orthophosphates by inorganic pyrophosphatase yields substantial free energy change around -33 kJ/mol, pulling polymerization equilibrium forward and making overall reaction essentially irreversible. ATP hydrolysis powers helicase and ligase steps but not polymerase condensation itself. Continuous removal of pyrophosphate prevents reverse pyrophosphorolysis reaction, ensuring high processivity and directionality of chain elongation while providing thermodynamic driving force independent of ATP supply.