Which enzyme extends the new DNA strand by adding nucleotides in the 5' to 3' direction?

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

Answer: (B)

DNA polymerase is the enzyme that extends the growing DNA strand during replication. It adds nucleotides to the 3' end of the new strand, building in the 5' to 3' direction by forming phosphodiester bonds and using the template strand to ensure correct base pairing. This directionality—adding to a 3' end—is a fundamental feature of DNA synthesis. Other enzymes have different roles: helicase unwinds the double helix, ligase seals nicks in the backbone, and RNA polymerase makes RNA (not DNA) and is involved in transcription or primer synthesis for DNA replication.