Which enzyme is responsible for unwinding the DNA double helix structure ahead of the replication fork?

The question asks for the enzyme responsible for unwinding the DNA double helix ahead of the replication fork.

• Helicase is the enzyme that unwinds the DNA double helix by breaking the hydrogen bonds between complementary base pairs, separating the two strands to create the replication fork.
• Topoisomerase relieves the supercoiling tension that builds up ahead of the replication fork as DNA is unwound.
• DNA Polymerase synthesizes new DNA strands.
• Ligase joins DNA fragments together.

Based on these functions, the enzyme responsible for unwinding the DNA double helix is Helicase.

The correct answer is D.

$$\boxed{\text{D. Helicase}}$$