DNA Structure and Replication · USMLE Step 1

Which enzyme joins Okazaki fragments on the lagging strand to create a continuous DNA strand?

  1. DNA polymerase I
  2. DNA polymerase III
  3. DNA ligase
  4. Topoisomerase
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Correct answer: DNA ligase

DNA ligase seals the sugar–phosphate backbone by forming phosphodiester bonds between adjacent Okazaki fragments, producing a continuous lagging strand.

Difficulty: Medium Question 5 of 20

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