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How does polymerase chain reaction make many copies of a DNA segment?
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cloning
The first clone of an adult mammal, Dolly the sheep, at the Roslin Institute, near Edinburgh.
The polymerase chain reaction (PCR) is a technique used to rapidly synthesize large quantities of a specific DNA segment by mimicking natural cellular replication. The process occurs in repeated cycles, with the number of copies doubling each time.12
Each cycle consists of three primary steps:
- Denaturation: The DNA sample is heated to approximately 95 °C (203 °F), which breaks the hydrogen bonds and separates the double-stranded DNA into two single strands.2
- Annealing: The temperature is reduced to about 55 °C (131 °F), allowing short primers to attach to their specific, complementary sequences on the single-stranded template.2
- Elongation: The temperature is raised to about 72 °C (162 °F). A heat-stable DNA polymerase binds to the primers and adds free nucleotides to synthesize a new complementary strand.2
By repeating this cycle 25 to 30 times, researchers can produce billions of copies of a target DNA fragment in just a few hours. This method is a vital tool in molecular biology and cloning research.23