In DNA replication, which enzyme is responsible for adding new nucleotides to the growing DNA strand in the $5\to 3$ direction?

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

Answer: (B)

Verified step by step guidance

1. Understand the directionality of DNA synthesis: DNA strands are synthesized in the 5\(\rightarrow\)3 direction, meaning new nucleotides are added to the 3' end of the growing strand.
2. Recall the role of DNA polymerase: This enzyme catalyzes the addition of nucleotides complementary to the template strand, extending the new DNA strand in the 5\(\rightarrow\)3 direction.
3. Differentiate DNA polymerase from other enzymes: DNA ligase joins Okazaki fragments, primase synthesizes RNA primers, and helicase unwinds the DNA double helix.
4. Conclude that the enzyme responsible for adding new nucleotides to the growing DNA strand in the 5\(\rightarrow\)3 direction is DNA polymerase.
5. Summarize that DNA polymerase reads the template strand and adds nucleotides one by one to the 3' end of the new strand, ensuring accurate DNA replication.