Which polymerase synthesizes the lagging strand in eukaryotes?

• A. DNA polymerase delta synthesizes the lagging strand.
• B. DNA polymerase epsilon synthesizes the lagging strand.
• C. DNA polymerase alpha synthesizes the lagging strand.
• D. DNA polymerase gamma synthesizes the lagging strand.

Answer: (A)

During eukaryotic DNA replication, the two strands are synthesized by different polymerases in a coordinated way. The leading strand is copied continuously in the direction of the replication fork by a polymerase specialized for that task, while the lagging strand is made discontinuously in short segments called Okazaki fragments. Each fragment starts with a primer laid down by a primase–DNA polymerase alpha complex, then the fragment is extended by a polymerase that handles the lagging-strand synthesis. The enzyme that does this extension for the lagging strand is DNA polymerase delta, which works with the sliding clamp to achieve high processivity on short fragments and then helps remove primers and join fragments. In contrast, DNA polymerase epsilon handles the leading strand, copying it smoothly in a continuous fashion. DNA polymerase gamma is the mitochondrial replicase, not involved in nuclear DNA replication. So the lagging strand is synthesized by DNA polymerase delta.