Polymerase chain reaction

Options

A. Is a method of synthesising human protein from human DNA
B. Uses restriction enzymes
C. Can produce billions of copies of a DNA fragment
D. Takes place naturally in bacteria

Answer

**Step-by-Step Text Solution for the Question: Polymerase Chain Reaction (PCR)**

1. **Definition of PCR**: Polymerase Chain Reaction (PCR) is a laboratory technique used to amplify specific DNA sequences, producing millions to billions of copies of a particular DNA fragment.

2. **Purpose of PCR**: The primary purpose of PCR is to make multiple copies of a DNA segment, which is essential for various applications in genetic engineering, forensic analysis, medical diagnostics, and research.

3. **In Vitro Technique**: PCR is performed in vitro, meaning it occurs outside of a living organism, under controlled laboratory conditions. This differentiates it from natural DNA replication, which occurs within cells.

4. **Components of PCR**:
- **DNA Template**: The DNA that contains the target sequence to be amplified.
- **Primers**: Short sequences of nucleotides that provide a starting point for DNA synthesis.
- **DNA Polymerase**: The enzyme responsible for synthesizing new DNA strands. The most commonly used polymerase in PCR is Taq polymerase, which is heat-stable.
- **Nucleotides**: The building blocks (adenine, thymine, cytosine, guanine) needed for new DNA strand synthesis.

5. **PCR Process**: The PCR process involves three main steps:
- **Denaturation**: The double-stranded DNA is heated to separate it into two single strands.
- **Annealing**: The temperature is lowered to allow primers to bind (anneal) to their complementary sequences on the single-stranded DNA.
- **Extension**: The temperature is raised again, allowing Taq polymerase to extend the primers, synthesizing new DNA strands.

6. **Cycle Repetition**: These three steps are repeated for 20-40 cycles, leading to exponential amplification of the target DNA sequence.

7. **Applications of PCR**: PCR is widely used in various fields, including:
- Genetic research
- Medical diagnostics (e.g., detecting pathogens)
- Forensic science (e.g., DNA profiling)
- Cloning and gene expression analysis

8. **Conclusion**: PCR is a fundamental technique in molecular biology that allows scientists to create large quantities of specific DNA sequences quickly and efficiently.