Question

What is the first step in a PCR reaction?

• A. Annealing
• B. Denaturation
• C. Extension
• D. Polymerization

Hint:

To copy DNA, you must first un-zip it. High-temperature denaturation is always step 1 of any PCR run.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Polymerase Chain Reaction (PCR) is a thermal cycling process that amplifies target DNA sequences through a series of temperature changes.

Step 2: Detailed Explanation:
A typical PCR cycle consists of three sequential steps:
1. Denaturation: The reaction mixture is heated to around \(94-98^{\circ}\text{C}\) to break the hydrogen bonds between complementary base pairs of the double-stranded DNA template, separating them into single strands.
2. Annealing: The temperature is lowered (usually to \(50-65^{\circ}\text{C}\)) to allow sequence-specific primers to bind to their complementary sites on the single-stranded DNA templates.
3. Extension/Polymerization: The temperature is raised to around \(72^{\circ}\text{C}\) so that DNA polymerase can synthesize the new DNA strand.
Therefore, the very first step of each cycle is denaturation.

Step 3: Final Answer:
Denaturation is the first step of a PCR cycle, allowing double-stranded DNA to separate.