Which of the following steps are catalysed by Taq polymerase in a PCR reaction ?

Options

A. Denaturation of template DNA
B. Annealing of primers to template DNA
C. Extension of primer end on the template DNA
D. All of the above

Answer

To determine which steps in a PCR reaction are catalyzed by Taq polymerase, we need to understand the three main steps of the PCR process: denaturation, annealing, and extension.

### Step-by-Step Solution:

1. **Understanding PCR**:
- PCR (Polymerase Chain Reaction) is a technique used to amplify specific segments of DNA, creating millions of copies of a particular DNA sequence.

2. **Identify the Steps of PCR**:
- **Denaturation**: This is the first step where the double-stranded DNA is heated to separate it into two single strands.
- **Annealing**: In this second step, short DNA primers bind to the single-stranded DNA templates, preparing them for the next step.
- **Extension**: This is the third step where Taq polymerase synthesizes new DNA strands by adding complementary nucleotides to the primers.

3. **Role of Taq Polymerase**:
- Taq polymerase is a heat-stable DNA polymerase derived from the bacterium Thermus aquaticus. Its primary function in PCR is during the extension phase.
- It catalyzes the addition of nucleotides to the growing DNA strand, effectively elongating the primer and synthesizing the new DNA strand.

4. **Conclusion**:
- Among the three steps of PCR, Taq polymerase specifically catalyzes the **extension** step, where it synthesizes new DNA strands. The other two steps, denaturation and annealing, do not involve Taq polymerase.

### Final Answer:
**Taq polymerase catalyzes the extension step in a PCR reaction.**

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