PCR stands for polymerase chain reaction, a laboratory method used to make many copies of a specific DNA sequence. By cycling through different temperatures and using a heat-stable DNA polymerase, the process replicates the target region exponentially.
Explanation
Polymerase chain reaction was developed in the 1980s as a way to amplify DNA without cloning it into living organisms. A PCR reaction contains template DNA, short oligonucleotide primers that flank the region to be copied, nucleotides, a buffering solution and a thermostable DNA polymerase such as Taq polymerase. The reaction is run in a thermal cycler that repeatedly changes the temperature. Each cycle has three steps: denaturation separates the double-stranded DNA, annealing allows primers to bind to complementary sequences and extension synthesizes new strands by adding nucleotides. Because the products of one cycle serve as templates for the next, the amount of DNA increases exponentially. Variations include reverse transcription PCR for RNA templates and quantitative PCR for measuring the amount of DNA in real time. PCR has become a basic tool in molecular biology for cloning, sequencing, mutagenesis and detection of genetic material.
Illustrative Examples
PCR is used in many diagnostic and research settings. Clinicians use PCR to detect viral and bacterial pathogens by amplifying their genetic material from patient samples, such as tests for influenza, HIV and SARS-CoV-2. In forensic science, PCR amplifies short tandem repeats from minute biological samples to generate genetic fingerprints. In evolutionary biology, PCR amplifies ancient DNA from fossils and museum specimens to study relationships among species. Environmental scientists use PCR to detect microbial populations in soil or water. These examples demonstrate how PCR can amplify tiny amounts of DNA and reveal information that would otherwise be undetectable.
PCR enables scientists to amplify specific DNA sequences efficiently and precisely. By combining primers, nucleotides and a thermostable polymerase under controlled temperature cycles, the technique generates large quantities of a target sequence. Its versatility has transformed diagnostics, forensic analysis and basic research.
Related Terms: DNA amplification, Taq polymerase, Real-time PCR, Reverse transcription PCR, Thermal cycler