Which of the following is the CORRECT sequence of PCR ?

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:

1. **Denaturation**: The first step in PCR involves heating the reaction mixture to a high temperature (typically around 94-98°C). This heat causes the double-stranded DNA to separate into two single strands. This process is crucial as it prepares the DNA template for the next steps.

2. **Annealing**: After denaturation, the temperature is lowered (usually to about 50-65°C) to allow the DNA primers to bind (or anneal) to the single-stranded DNA templates. The primers are short sequences of nucleotides that are complementary to the target DNA sequence. This step is essential for initiating the synthesis of the new DNA strands.

3. **Extension**: The final step involves raising the temperature again (typically to around 72°C), which is optimal for the enzyme Taq polymerase to synthesize new DNA strands. The Taq polymerase extends the primers, adding nucleotides to form a new strand of DNA complementary to the template strand.

Now, putting these steps together, the correct sequence of PCR is:
- **Denaturation**
- **Annealing**
- **Extension**

Thus, the correct answer is **Option 1: Denaturation, Annealing, Extension**.