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DNA Replication: Helicase and Unwinding
Before DNA replication actually begins, a special type of enzyme called DNA helicase must move along the double-stranded DNA molecule and locate a region known as the origin of replication. Once it reaches this location, the DNA helicase will bind to it via electric forces and begin the process of unwinding. During this process, the helicase moves along the DNA and breaks the hydrogen bonds between the nitrogenous base, which exposes the single-strands of DNA. The position of the helicase as it moves along is known as the fork of replication. This unwinding process creates positive supercoils in the DNA molecule, which increases the stress of the molecule and makes it difficult for further unwinding to take place. Another enzyme called DNA gyrase actually binds to the DNA and decreases the stress involved with unwinding by introducing negative supercoils.
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