Practice question

Okazaki fragment synthesis inevitably leaves gaps between fragments after primer removal. Pol I synthesizes DNA to fill those short single-strand gaps using upstream 3' OH as primer ensuring precise replacement of RNA with DNA in 5' to 3' direction. Once filling complete, adjacent fragments remain connected by single phosphodiester nick because polymerase cannot create final bond between 3' hydroxyl and 5' phosphate. DNA ligase using NAD+ cofactor in bacteria hydrolyzes to close nick forming continuous phosphodiester backbone. Requirement for both enzymes couples gap filling and final ligation.