Which of he following is'the correct sequence of PCR or polymerase chain reaction

Options

A. Denaturation `rarr` Annealing `rarr` Extension
B. Extension `rarr` Denaturation `rarr` Annealing
C. Annealing `rarr` Extension `rarr` Denaturation
D. Denaturation `rarr` Extension `rarr`Annealing

Answer

To determine the correct sequence of the Polymerase Chain Reaction (PCR), we need to understand the three main steps involved in the process: denaturation, annealing, and extension. Here’s a step-by-step breakdown of the correct sequence:

### Step 1: Denaturation
- **Description**: The first step of PCR involves heating the double-stranded DNA (dsDNA) to a high temperature (typically around 94-98°C). This heat breaks the hydrogen bonds between the two strands of DNA, resulting in two single-stranded DNA (ssDNA) molecules.
- **Purpose**: This step is crucial as it separates the DNA strands, making them available for the next step.

### Step 2: Annealing
- **Description**: After denaturation, the temperature is lowered (usually to around 50-65°C) to allow primers to bind (anneal) to the single-stranded DNA. Primers are short sequences of nucleotides that are complementary to the target DNA sequence.
- **Purpose**: This step ensures that the primers are correctly positioned on the DNA strands for the next step.

### Step 3: Extension
- **Description**: The temperature is then raised to around 72°C, which is the optimal temperature for the enzyme Taq Polymerase. This enzyme synthesizes new DNA strands by adding nucleotides to the primers, effectively extending the DNA strands.
- **Purpose**: This step results in the formation of new double-stranded DNA molecules.

### Conclusion
The correct sequence of PCR is:
1. Denaturation
2. Annealing
3. Extension

Thus, the correct option is the first one: **Denaturation, Annealing, Extension**.

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