Which enzyme elongates DNA in the 5' to 3' direction?

Which enzyme elongates DNA in the 5' to 3' direction?

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

Answer: (C)

DNA synthesis can only add nucleotides to a free 3' end, so the enzyme that elongates the new strand does so in the 5' to 3' direction. DNA polymerase III is the main replicative polymerase in bacteria and carries out the bulk of this elongation by continuously adding dNTPs to the 3' end of the growing strand, working off the template that runs 3' to 5'. The other enzymes have different roles: helicase unwinds the DNA double helix, primase creates the RNA primer to start synthesis, and ligase seals the gaps between fragments after synthesis is completed.

DNA synthesis can only add nucleotides to a free 3' end, so the enzyme that elongates the new strand does so in the 5' to 3' direction. DNA polymerase III is the main replicative polymerase in bacteria and carries out the bulk of this elongation by continuously adding dNTPs to the 3' end of the growing strand, working off the template that runs 3' to 5'.

The other enzymes have different roles: helicase unwinds the DNA double helix, primase creates the RNA primer to start synthesis, and ligase seals the gaps between fragments after synthesis is completed.