Polymerase Chain Reaction (PCR)
MCAT glossary · Biological & Biochemical Foundations of Living Systems
Definition
In vitro DNA amplification using thermal cycling: denaturation (95°C), annealing (~55°C), extension (72°C) with Taq polymerase.
Polymerase Chain Reaction (PCR) in plain English
PCR is a molecular photocopier: you start with a tiny, maybe invisible amount of DNA and make millions of copies so scientists can actually study it (it's the engine behind DNA tests and many COVID tests). It works by repeatedly cycling the temperature. Heating to about 95°C ('denaturation') pries the DNA's two strands apart; cooling to ~55°C ('annealing') lets short guide pieces called primers stick to the spot you want copied; and 72°C ('extension') lets a heat-proof enzyme, Taq polymerase, build the new matching strands. Each cycle doubles the DNA, so after ~30 rounds one molecule becomes over a billion.
Also called: PCR
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