## **Core Concept**
The Polymerase Chain Reaction (PCR) is a laboratory technique used to amplify specific segments of DNA. It involves repetitive cycles of denaturation, annealing, and extension to generate millions of copies of a target DNA sequence. The process relies on thermostable DNA polymerases, such as **Taq polymerase**.
## **Why the Correct Answer is Right**
The correct sequence of steps in PCR is:
1. **Denaturation**: The double-stranded DNA is heated to separate it into two single strands.
2. **Annealing**: The temperature is lowered to allow primers to bind to their complementary sequences on the single-stranded DNA.
3. **Extension**: The temperature is raised to the optimal level for the **Taq polymerase** to synthesize new DNA strands by adding nucleotides to the primers.
## **Why Each Wrong Option is Incorrect**
- **Option A:** Incorrect because it does not accurately represent the sequence of denaturation, annealing, and extension.
- **Option B:** Incorrect as it likely misrepresents the order or includes incorrect steps.
- **Option D:** Incorrect because it also does not accurately represent the correct sequence of PCR steps.
## **Clinical Pearl / High-Yield Fact**
A key point to remember is that the **Taq polymerase** is used in PCR because it is thermostable, meaning it can withstand the high temperatures required for DNA denaturation without losing its activity. This makes it essential for the cyclic process of PCR.