During DNA replication, what is the primary role of DNA polymerase?

• A. It unwinds the DNA double helix by breaking hydrogen bonds between complementary bases.
• B. It seals nicks between Okazaki fragments by forming phosphodiester bonds in the sugar-phosphate backbone.
• C. It lays down short RNA primers to provide a free $3^{\prime }$ end for DNA synthesis.
• D. It synthesizes a new DNA strand by adding nucleotides to the $3^{\prime }$ end using the template strand for base pairing.

Answer: (D)

Verified step by step guidance

1. Understand the process of DNA replication, which involves unwinding the DNA double helix, synthesizing new strands, and joining fragments.
2. Identify the specific function of DNA polymerase: it synthesizes new DNA strands by adding nucleotides complementary to the template strand.
3. Recall that DNA polymerase can only add nucleotides to the 3\' end of a growing DNA strand, meaning synthesis occurs in the 5\' to 3\' direction.
4. Distinguish DNA polymerase's role from other enzymes: helicase unwinds DNA, primase lays down RNA primers, and ligase seals nicks between Okazaki fragments.
5. Conclude that the primary role of DNA polymerase is to catalyze the formation of phosphodiester bonds between nucleotides, extending the DNA strand by adding nucleotides to the 3\' end using the template strand for base pairing.