Which enzyme synthesizes new DNA on the leading and lagging strands?

• A. Helicase
• B. Primase
• C. DNA polymerase
• D. Ligase

Answer: (C)

DNA polymerase is the enzyme that builds new DNA by adding nucleotides to a pre-existing strand. On the leading strand it works continuously toward the replication fork, while on the lagging strand it synthesizes short segments (Okazaki fragments) away from the fork. It can only extend an existing chain and needs a primer laid down by primase to start, which is why primers are essential for initiation on the lagging strand. After each fragment is produced, DNA ligase seals the gaps. Other enzymes like helicase, primase, and ligase have crucial roles in replication, but they do not directly synthesize new DNA; DNA polymerase does.