Polymerase Chain Reaction

Many of the processes employed in genetic testing and research, including as the study of historical DNA samples and the detection of infectious pathogens, are fundamentally based on CR. By using PCR, copies of extremely tiny quantities of DNA sequences are exponentially amplified over a number of temperature-changing cycles. Today, PCR is a widely used and frequently essential technology in medical laboratory research for a wide range of applications, including biological research and criminal forensics. The bulk of PCR techniques rely on heat cycling. To enable various temperature-dependent processes, such as DNA melting and enzyme-driven DNA replication, thermal cycling exposes reactants to repeated cycles of heating and cooling. PCR uses two primary reagents: primers (short single-strand DNA fragments known as oligonucleotides that are complementary to a DNA polymerase (to the target DNA region) are required. In the first stage of PCR, a procedure known as nucleic acid denaturation physically separates the two strands of the DNA double helix at a high temperature. The temperature is decreased in the second stage, and the primers bind to the complementary DNA sequences. The two DNA strands then serve as templates for DNA polymerase, which uses free nucleotides—building DNA's blocks—to enzymatically put together a new DNA strand. The DNA created during PCR is used as a template for replication of itself, which triggers a chain reaction that exponentially amplifies the original DNA template.