In the polymerase chain reaction, the optimum temperature for the extension step is

Options

A. `72^@C`
B. `50^@C`
C. `90^@C`
D. `45^@C`

Answer

To solve the question regarding the optimum temperature for the extension step in the polymerase chain reaction (PCR), we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Process of PCR**:
- PCR is a technique used to amplify specific segments of DNA, creating multiple copies of a particular DNA sequence.

2. **Identify the Steps of PCR**:
- PCR consists of three main steps: denaturation, annealing, and extension.
- **Denaturation**: The double-stranded DNA is heated to separate it into two single strands. This typically occurs at around 94°C.
- **Annealing**: The temperature is lowered to allow primers to bind to the single-stranded DNA. This usually occurs at a temperature between 50°C and 65°C, depending on the primers used.
- **Extension**: The temperature is raised to allow the DNA polymerase to synthesize new DNA strands.

3. **Determine the Optimum Temperature for Extension**:
- The enzyme commonly used in PCR is Taq polymerase, which is derived from the bacterium Thermus aquaticus. This enzyme is thermostable and functions optimally at higher temperatures.
- The optimum temperature for the extension step, where the DNA polymerase synthesizes new DNA strands, is typically around **72°C**.

4. **Select the Correct Answer**:
- Given the options: 72°C, 50°C, 90°C, and 45°C, the correct answer for the optimum temperature for the extension step in PCR is **72°C**.

### Final Answer:
The optimum temperature for the extension step in the polymerase chain reaction is **72°C**.

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