The Polymerase Chain Reaction

The polymerase chain reaction, or PCR, is a crucial method for exponentially increasing the amount of a specific DNA sequence.

PCR is a cyclic process controlled by the temperature of the reaction mixture. First, the temperature is raised to 95°C (205°F), causing the ‘template’ DNA to separate (denature).

The temperature is then decreased to around 50°C (122°F), allowing short ‘primer’ pieces of DNA to hybridise to each strand of the template at opposite ends of the sequence to be amplified.

The thermostable enzyme Taq (a DNA polymerase that is active at high temperatures) then binds to and extends the primers at an intermediate temperature of 72°C (162°F), so that two new double-stranded copies of the template are made.

This cyclic process of separating DNA strands, copying and reannealing the daughter strands is repeated multiple times to increase the numbers of DNA product.

Interactive tutorial

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