What is the primary enzyme responsible for adding nucleotides during DNA synthesis?

The primary enzyme responsible for adding nucleotides during DNA synthesis is DNA polymerase. This enzyme plays a crucial role in the replication of DNA by catalyzing the formation of the phosphodiester bonds between individual nucleotides, which results in the elongation of the new DNA strand. DNA polymerase requires a template strand to guide the synthesis of a complementary strand, ensuring that the newly synthesized DNA matches the original template.

During the replication process, DNA polymerase also has proofreading capabilities, allowing it to correct mistakes in nucleotide incorporation, thus maintaining the integrity of the genetic information. Its activity is essential for both cellular division and the repair of damaged DNA, making it a key player in molecular biology.

The other enzymes mentioned, while important in their respective roles, do not primarily add nucleotides during DNA synthesis. RNA polymerase is involved in synthesizing RNA from a DNA template, DNA ligase is responsible for joining Okazaki fragments on the lagging strand during DNA replication, and topoisomerase helps relieve the tension in the DNA helix ahead of the replication fork. Thus, the unique function of DNA polymerase makes it the correct answer to the question regarding the primary agent in nucleotide addition during DNA synthesis.