Which enzyme joins individual nucleotides to replicate a DNA molecule and proofreads?

Which enzyme joins individual nucleotides to replicate a DNA molecule and proofreads?

• A. DNA ligase
• B. SSB proteins
• C. Topoisomerase
• D. DNA polymerase

Answer: (D)

The enzyme that does this is DNA polymerase. During DNA replication, it adds nucleotides one by one to the growing strand, using the original strand as a template, and builds the new strand in a 5' to 3' direction. What makes DNA polymerase especially important is its proofreading ability: it has a 3' to 5' exonuclease activity that removes a mismatched nucleotide right after it’s incorporated, allowing the correct nucleotide to be added in its place. This combination of synthesis and immediate error correction gives DNA polymerase high fidelity during replication. Other enzymes have different roles: DNA ligase seals the gaps between Okazaki fragments, SSB proteins stabilize single-stranded DNA, and topoisomerase relieves twisting tension ahead of the replication fork.

The enzyme that does this is DNA polymerase. During DNA replication, it adds nucleotides one by one to the growing strand, using the original strand as a template, and builds the new strand in a 5' to 3' direction. What makes DNA polymerase especially important is its proofreading ability: it has a 3' to 5' exonuclease activity that removes a mismatched nucleotide right after it’s incorporated, allowing the correct nucleotide to be added in its place. This combination of synthesis and immediate error correction gives DNA polymerase high fidelity during replication. Other enzymes have different roles: DNA ligase seals the gaps between Okazaki fragments, SSB proteins stabilize single-stranded DNA, and topoisomerase relieves twisting tension ahead of the replication fork.