## Core Concept
The process of DNA replication and transcription requires the double helix to be unwound, allowing access to the genetic material. This unwinding is facilitated by specific enzymes. The key concept here involves understanding the role of helicases in DNA metabolism.

## Why the Correct Answer is Right
The correct answer, **Helicase**, is the enzyme directly responsible for unwinding the double-stranded DNA into single strands by breaking the hydrogen bonds between the nucleotide bases. This action is crucial for DNA replication and repair, as well as for transcription. Helicase uses the energy from ATP hydrolysis to unwind the DNA double helix, creating a replication fork where DNA synthesis can occur.

## Why Each Wrong Option is Incorrect
- **Option A: Polymerase** - This enzyme is involved in adding nucleotides to a growing DNA strand during replication and repair but does not unwind DNA.
- **Option B: Ligase** - This enzyme seals gaps in the DNA by forming a phosphodiester bond between a 5' phosphate and a 3' hydroxyl group, crucial for DNA replication and repair, but it does not unwind DNA.
- **Option D: Topoisomerase** - While this enzyme does play a role in DNA replication by relieving supercoiling ahead of the replication fork, it does not directly unwind DNA like helicase does.

## Clinical Pearl / High-Yield Fact
A key point to remember is that helicases are essential for initiating DNA replication and transcription. Inhibitors of helicases are being explored for their potential as anticancer drugs, as they could prevent cancer cells from replicating their DNA.

## Correct Answer: C. Helicase