Which of the following steps are catalysed by Taq polymerase in a PCR reaction ?
(a) Denaturation of template DNA
(b) Annealing of primers to template DNA
(c) Extension of primer and on the template DNA
(d) All of the above

Options

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

Explanation

To determine which steps are catalyzed by Taq polymerase in a PCR reaction, we need to understand the role of Taq polymerase and the steps involved in the PCR process.

### Step-by-Step Solution:

1. **Understanding PCR**: PCR (Polymerase Chain Reaction) is a technique used to amplify a specific segment of DNA. It involves three main steps: denaturation, annealing, and extension.

2. **Denaturation**: In the first step, the double-stranded DNA is heated to a high temperature (usually around 94-98°C). This heat breaks the hydrogen bonds between the complementary base pairs, resulting in two single-stranded DNA molecules. **Taq polymerase does not catalyze this step**; it is a physical process driven by heat.

3. **Annealing**: In the second step, the temperature is lowered (typically to around 50-65°C) to allow short DNA primers to bind (anneal) to their complementary sequences on the single-stranded DNA templates. **Taq polymerase does not catalyze this step** either; it is a process that relies on the properties of the primers.

4. **Extension**: In the final step, the temperature is raised again to around 72°C, which is the optimal temperature for Taq polymerase activity. Taq polymerase synthesizes new DNA strands by adding nucleotides to the 3' ends of the primers, thereby extending the DNA strand. **This step is catalyzed by Taq polymerase**.

5. **Conclusion**: Since Taq polymerase catalyzes only the extension step and not the denaturation or annealing steps, the correct answer to the question is **(c) Extension of primer on the template DNA**.

### Final Answer:
(c) Extension of primer on the template DNA.