8.7: Polymerase Chain Reaction (PCR)

The polymerase chain reaction (PCR) is a powerful and widely used laboratory technique that allows scientists to amplify millions of copies of a specific DNA sequence in a relatively short time. Developed in the 1980s, PCR revolutionized molecular biology by enabling researchers to amplify tiny amounts of DNA for analysis, cloning, or sequencing.

PCR works through a series of temperature-controlled steps. The first step, denaturation, involves heating the DNA sample to a high temperature, which separates the double-stranded DNA molecule into two single strands. In the second step, known as annealing, the temperature is lowered so that short DNA sequences, called primers, can bind to complementary regions of the single-stranded DNA templates. These primers mark the starting points for DNA synthesis.

The third step, elongation, occurs when a heat-stable DNA polymerase enzyme extends the primers by adding nucleotides to form new complementary DNA strands. This results in the duplication of the target DNA region. Each PCR cycle doubles the amount of DNA, and after many cycles, a very large number of copies of the original DNA sequence are produced. Because of its efficiency and sensitivity, PCR is widely used in research, medical diagnostics, forensic science, and biotechnology.

Image credit: Louis Reed on Unsplash Link to test tube image [unsplash.com]

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