Polymerase chain reaction (PCR)
The polymerase chain reaction (PCR) is a technique that is used to make multiple copies of a piece of DNA.
PCR is carried out in vitro, but mimics what happens in cells when DNA is copied (replicated) prior to cell division.
How does PCR work?
Before PCR can occur, the two strands in the DNA double helix need to be separated. This is called denaturation. It is done by raising the temperature of the DNA solution. This causes the hydrogen bonds between the complementary DNA chains to break, and the two strands separate.
Next, the temperature is lowered and an enzyme (usually Taq polymerase) joins free DNA nucleotides together. The order in which these nucleotides are joined to the new strand is determined by the sequence of nucleotides in the original DNA strand which is being copied.
The result is a double stranded DNA molecule which contains one newly made strand and one original strand.
Next, the newly created double helix is separated (by heating the solution) and the cycle is repeated.
When is PCR used?
PCR can be used for a range of different purposes, for example:
- 20 November 2007