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 solve the question regarding the correct sequence of the Polymerase Chain Reaction (PCR), we will break down the process into its three main steps: denaturation, annealing, and extension.

### Step-by-Step Solution:

1. **Denaturation**:
- The first step in the PCR process is denaturation. During this step, the double-stranded DNA is heated to around 94°C. This high temperature causes the hydrogen bonds between the complementary bases of the DNA strands to break, resulting in the separation of the two strands. This step is crucial as it prepares the DNA for the next steps by creating single-stranded templates.

**Hint**: Remember that denaturation involves breaking the hydrogen bonds between DNA strands, leading to their separation.

2. **Annealing**:
- The second step is annealing. After denaturation, the temperature is lowered (typically between 45°C to 65°C) to allow short DNA primers to bind (or anneal) to the single-stranded DNA templates. Primers are essential for the synthesis of new DNA strands because they provide a starting point for DNA polymerase to begin replication.

**Hint**: Annealing is about the primers binding to the template strands; think of it as the primers "finding their place" on the DNA.

3. **Extension**:
- The final step is extension (or elongation). The temperature is raised to approximately 72°C, which is the optimal temperature for the enzyme Taq DNA polymerase to function. During this step, Taq polymerase adds nucleotides to the 3' end of the primers, synthesizing new DNA strands complementary to the template strands. This results in the formation of new double-stranded DNA.

**Hint**: Extension is where the actual DNA synthesis occurs; visualize it as the construction phase where new DNA strands are built.

### Conclusion:
The correct sequence of the PCR process is:
- **Denaturation → Annealing → Extension**

Thus, the answer to the question is the sequence: **Denaturation, Annealing, Extension**.