Let's look at the key terms you need to know: 1. An enzyme called helicase unwinds the double-stranded DNA 2. Primer binds to the end of the DNA strand. Primers are short RNA molecules that act as templates for the starting point of DNA replication. 3. An enzyme complex called DNA polymerase "walks" down the DNA strands and adds free nucleotides to each strand. The nucleotides pair with the complementary nucleotides on the existing stand (A with T, G with C). 4. An enzyme called DNA ligase seals up the fragments into one long continuous strand