Practice question

DNA polymerase active site structurally restricts addition to 3' terminus, moving along template 3' to 5' while synthesizing new strand 5' to 3' opposite direction. Nucleotide triphosphate binds with sugar oriented allowing hydroxyl attack; incoming base pairing verified before catalysis. Because template is read opposite, double helix grows antiparallel, semidiscontinuous leading to continuous leading strand advancing with fork and discontinuous lagging strand via Okazaki fragments. Directionality ensures high-fidelity Watson-Crick pairing and couples polymerization to pyrophosphate release driving forward reaction. No known DNA polymerase synthesizes 3' to 5' chain.