PCR (Polymerase Chain Reaction) is a laboratory technique used to make many copies of a specific DNA segment. It allows scientists to take a very small sample of DNA and amplify it into millions of identical copies in a short time.
Here’s how it works:
- Purpose:
PCR helps scientists study DNA even when only a tiny amount is available — for example, in crime scenes, medical tests, or genetic research. - Main idea:
It mimics the natural process of DNA replication but is done in a test tube using a machine called a thermal cycler. - Steps of PCR:
PCR happens in three main steps, repeated many times (usually 25–35 cycles):- Denaturation:
The double-stranded DNA is heated (around 94–96°C) so that it separates into two single strands. - Annealing:
The temperature is lowered (around 50–65°C) so short pieces of DNA called primers can attach to the target sequences on each strand. - Extension:
The temperature is raised again (around 72°C), and an enzyme called Taq polymerase adds new nucleotides to build new DNA strands, copying the target region.
- Denaturation:
- Result:
After each cycle, the amount of target DNA doubles. After many cycles, millions of copies of the specific DNA sequence are produced. - Uses of PCR:
- Detecting genetic diseases
- Identifying criminals or victims (forensic science)
- Diagnosing infections (like detecting viruses or bacteria)
- Research in genetics and molecular biology
In simple words, PCR is like a DNA photocopier — it makes many copies of a specific piece of DNA so scientists can study it in detail.