PCR - what is it and what is the point?

This is a basic introduction to PCR, basically for biochem. noobies. Please do not copy this without asking.

PCR is one of the most essential methods in biochemistry, molecular biology, medicine and forensic science. The procedure can be described as an imitation of the DNA replication that takes place during each mitosis. During PCR all of the enzymes involved, except for the DNApolymerase, have been replaced by heat cycles. Furthermore a PCR buffer, containing two kinds of primers as well as all four nucleotides necessary to build the DNA strands, is necessary to provide an optimal environment for the polymerase. Mg2+ is also an essential ingredient of the buffer since this cation stabilizes the hybridization of primers to the single strands of DNA as well as the bonds between the nucleotides and the DNA polymerase. The DNA polymerase is derived from organisms tolerant to extreme heat, thus able to function even at the high temperatures needed to denature the

DNA molecules. To begin with, the DNA sample of interest is exposed to a temperature of 92°C , thus denaturing the molecule and causing its strands to separate. Then a temperature of approximately 55°C (depending on the lengths of primers and gene fragments) causes the forward and reverse primers to hybridize to one single strand each. The free OH - -ends of the primers allow the DNA polymerase to find its way to the template and begin to build a complementary strand. The whole routine is repeated approximately thirty times, causing the numbers of DNA molecules to increase exponentially and resulting in roughly 1 million copies in only 30 minutes. In short; one of the main advantages of the PCR method is that it provides amplification of the gene of interest, thus ensuring that scientists have endless amounts of the material they want to study.

Kary Mullis won the Nobel Price in 1993 for inventing the method. Some argued at the time that the method is too "simple" for its inventor to earn this honour. However, the incredible advantages that the method has provided to science cannot be underestimated.