What enzyme catalyzes the addition of nucleotides during DNA replication?

DNA polymerase is the enzyme that catalyzes the addition of nucleotides during DNA replication. It builds a new DNA strand by joining complementary deoxyribonucleotides to the 3′ end of a growing strand.

DNA polymerase cannot usually begin a strand from nothing. It needs a short RNA primer whose exposed 3′ hydroxyl group provides the starting point. The enzyme then synthesizes DNA in the 5′-to-3′ direction, matching each incoming nucleotide to the template strand.

Replication involves several cooperating enzymes. Helicase unwinds the double helix, primase makes the RNA primer, and ligase seals breaks between DNA fragments. On the lagging strand, DNA polymerase produces short Okazaki fragments that are later joined by ligase. RNA polymerase is not the main replication enzyme; it makes RNA during transcription.

Many organisms have several DNA polymerases with different jobs. Some copy the genome, while others repair damage or remove primers. Their proofreading activity also helps keep replication highly accurate by removing many incorrectly inserted nucleotides.