Which of the following shows the correct sequence of processes with respect to the PCR ?

Options

A. Extension , denaturation , annealing
B. Denaturation , annealing , extension
C. Denaturation , extension , annealing
D. Annealing , extension , denaturation

Answer

To determine the correct sequence of processes in the Polymerase Chain Reaction (PCR), we need to understand the three main steps involved in this technique. Here’s a step-by-step breakdown of the processes:

### Step 1: Denaturation
- **Description**: The first step in PCR is denaturation. This involves heating the DNA sample to a high temperature (typically around 95°C). The heat causes the double-stranded DNA to separate into two single strands by breaking the hydrogen bonds between the base pairs.
- **Purpose**: This step is crucial because it prepares the DNA template for the next steps by making the strands accessible for the primers.

### Step 2: Annealing
- **Description**: After denaturation, the temperature is lowered (usually to around 50-65°C) to allow the primers to bind, or anneal, to the single-stranded DNA. Primers are short sequences of nucleotides that are complementary to the target DNA sequence.
- **Purpose**: This step ensures that the primers are properly aligned with the target DNA sequence, which is essential for the synthesis of new DNA strands in the next step.

### Step 3: Extension
- **Description**: The final step is extension, where the temperature is raised again (typically to around 72°C). In this step, a DNA polymerase enzyme synthesizes a new DNA strand by adding nucleotides to the 3' end of the primers.
- **Purpose**: This step amplifies the DNA, creating new copies of the target sequence.

### Conclusion
Based on the above steps, the correct sequence of processes in PCR is:
- **Denaturation → Annealing → Extension**

Thus, the correct answer to the question is **Option B: Denaturation, Annealing, Extension**.

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