Question

The unwinding of DNA during replication is done by:

• A. DNA polymerase
• B. Ligase
• C. Helicase
• D. Primase

Hint:

Helicase is often called the “unzipping enzyme” because it breaks hydrogen bonds between base pairs and opens the DNA double helix during replication.

Answer 1

The Correct Option is C

Concept: DNA replication is the process by which a DNA molecule produces two identical copies of itself. During this process, the double-stranded DNA must first be separated so that each strand can act as a template for synthesis of a new strand. Several enzymes participate in DNA replication, each performing a specific function.
• Helicase – Unwinds the DNA double helix by breaking hydrogen bonds between base pairs.
• DNA polymerase – Synthesizes the new DNA strand by adding nucleotides.
• Primase – Synthesizes short RNA primers needed to start DNA synthesis.
• Ligase – Joins fragments of DNA (especially Okazaki fragments) by forming phosphodiester bonds.

Step 1: Understand the first step of DNA replication.
During replication, the DNA double helix must first open so that the two strands can separate. This separation occurs at a region called the replication fork.

Step 2: Identify the enzyme responsible for unwinding DNA.
The enzyme helicase moves along the DNA molecule and breaks the hydrogen bonds between complementary base pairs. This action unwinds the double helix and separates the two strands. \[ \text{DNA double helix} \xrightarrow{\text{Helicase}} \text{Two single DNA strands} \]

Step 3: Eliminate the incorrect options.
• DNA polymerase: Responsible for synthesizing new DNA strands.
• Ligase: Joins DNA fragments during replication.
• Primase: Produces RNA primers needed to initiate DNA synthesis. None of these enzymes unwind the DNA helix.

Step 4: Select the correct answer. Thus, the enzyme responsible for unwinding DNA during replication is: \[ Helicase \]