PCR is a method for amplifying DNA fragments rapidly and efficiently.

'Amplifying' means that a large number of DNA fragments are being produced.

Specific DNA polymerases, like Taq polymerase, are used for their ability to withstand high temperatures without denaturing.

Primers are short nucleotide sequences that bind to complementary DNA strands, initiating replication.

1. DNA fragment to act as a template
2. Primers
3. DNA polymerase
4. Free nucleotides
5. A thermocycler

Denaturation - heating the DNA to 95°C to break the hydrogen bonds between complementary strands and separate them.

Annealing - cooling to 55°C so primers can bind to the DNA strands by forming hydrogen bonds.

The primers provide DNA sequences for DNA polymerase to attach to and prevent the two strands from rejoining.

Extension - heating to 72°C for DNA polymerase to synthesise new DNA.

Free deoxynucleotide triphosphate molecules (dNTPs) provide the energy for the formation of phosphodiester bonds.

A thermocycler precisely varies temperatures for the various PCR stages.

1. PCR can rapidly make billions of copies of a DNA segment.
2. PCR does not require living cells.

Nucleotides provide the bases that are added to form the new strands of DNA.