How does the polymerase chain reaction amplify a specific DNA sequence?

The polymerase chain reaction (PCR) is a laboratory technique used to rapidly generate millions of copies of a specific DNA segment. The process relies on repeated cycles of three distinct steps, which mimic natural DNA replication:21

• Denaturation: The DNA sample is heated (to approximately 95 °C), causing the hydrogen bonds to break and the double-stranded DNA to separate into two single strands.1
• Annealing: The temperature is lowered (to about 55 °C), allowing short, synthetic primers to bind to their complementary sequences on the single-stranded template.21
• Elongation (Extension): The temperature is raised (to about 72 °C), enabling DNA polymerase—typically a heat-stable version known as Taq—to add nucleotides to the primers, synthesizing a new complementary strand.1

Because the number of DNA copies doubles with each cycle, performing 25 to 30 cycles can produce a sufficient quantity of the target sequence for use in molecular biology, forensic analysis, and medical diagnostics.21