So this is our helicase molecules. So let's suppose the helicase enzyme moves along our DNA molecule very quickly until it reaches the origin of replication which is shown here. Now notice that each one of these pair of bases are held together by hydrogen bonds. Now when our helicase binds to the origin of replication it begins to move more slowly. And as it moves, let's suppose it moves from right to left along the double stranded DNA molecule. It begins to unzip or unwind that double stranded DNA.