Which of these statements about Taq polymerase used during PCR is not correct ?

Options

A. It is used for primer extension to synthesise a new DNA strand
B. It is a thermostable enzyme and can survive temperatures up to `125^@C`
C. It is obtained from Thermus aquaticus
D. Its addition eliminated the need to add fresh polymerase in every PCR cycle

Answer

To determine which statement about Taq polymerase used during PCR is not correct, we will analyze each option step by step.

### Step-by-Step Solution:

1. **Understanding Taq Polymerase**: Taq polymerase is an enzyme used in the Polymerase Chain Reaction (PCR) to synthesize new DNA strands. It is derived from the bacterium Thermus aquaticus, which is known for its ability to withstand high temperatures.

2. **Analyzing the Statements**:
- **Statement 1**: "It is used for primer extension."
- This statement is correct. Taq polymerase is indeed used to extend primers during the PCR process to synthesize new DNA strands.

- **Statement 2**: "It is a thermostable enzyme that can survive temperatures up to 125 degrees Celsius."
- This statement is incorrect. While Taq polymerase is thermostable and can function at high temperatures (up to about 95 degrees Celsius), it does not survive temperatures as high as 125 degrees Celsius. This is the incorrect statement we are looking for.

- **Statement 3**: "It is obtained from Thermus aquaticus."
- This statement is correct. Taq polymerase is extracted from the bacterium Thermus aquaticus.

- **Statement 4**: "It is necessary to add fresh polymerase in every PCR cycle."
- This statement is correct. In traditional PCR, Taq polymerase can lose activity over multiple cycles, and it is often necessary to add fresh polymerase for each cycle to maintain efficiency.

3. **Conclusion**: The statement that is not correct is **Statement 2**, which claims that Taq polymerase can survive temperatures up to 125 degrees Celsius.

### Final Answer:
The incorrect statement about Taq polymerase used during PCR is: **"It is a thermostable enzyme that can survive temperatures up to 125 degrees Celsius."**

---