What does the term unzipping refer to in dna replication

The term "unzipping" in the DNA replication refers to the breaking of the hydrogen bonds.
In the process of DNA replication, DNA helicases disentangle DNA at positions known as origins where synthesis will be initiated. DNA   helicases continue to uncoil the DNA  creating a structure called replication fork as they unzipped apart. The process of breaking the hydrogen bonds between the nucleotide base pairs in double-stranded DNA needs energy. Helicases require energy stored in an ATP molecule to break the bonds.  

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