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Why is DNA uncoiled before replication? DNA replication requires that the complementary strands separate. A new complementary strand is then synthesized onto each of the existing strands. The end result is two double stranded molecules. If the original strand did not uncoil then, even if synthesis was possible, the two new molecules would be hopelessly entangled. In DNA synthesis events occur in the following order: a portion of the original molecule uncoils and the two strands separate in that region. Then DNA polymerase synthesizes complementary strands. Finally the two strands for each new molecule attach and coil up.