polimerázláncreakció

A polimerázláncreakció, often abbreviated as PCR, is a laboratory technique used to amplify (make many copies of) a specific segment of DNA. This process mimics the natural DNA replication that occurs in living organisms but is performed in vitro, meaning in a test tube. PCR requires a DNA template containing the target sequence, a pair of primers that flank the target sequence, a heat-stable DNA polymerase enzyme, and nucleotides (the building blocks of DNA).

The PCR cycle consists of three main steps: denaturation, annealing, and extension. In denaturation, the DNA sample is heated to a high temperature, typically around 94-98 degrees Celsius, which breaks the hydrogen bonds holding the two strands of the DNA double helix together, separating them into single strands. In annealing, the temperature is lowered to around 50-65 degrees Celsius, allowing the primers to bind (anneal) to their complementary sequences on the single-stranded DNA templates. Finally, in extension, the temperature is raised to the optimal working temperature for the DNA polymerase, usually around 70-72 degrees Celsius. The polymerase then extends the primers by adding nucleotides, synthesizing new DNA strands complementary to the template strands.

Each cycle of PCR effectively doubles the amount of the target DNA sequence. By repeating these cycles numerous times (typically 20-40), a single starting molecule of DNA can be amplified into billions of copies. This amplification makes it possible to detect and analyze even very small amounts of DNA. PCR has become an indispensable tool in molecular biology, genetics, forensics, medicine, and many other fields, enabling applications such as DNA sequencing, gene cloning, disease diagnosis, and Paternity testing.