Polymerase Chain Reaction

The polymerase chain reaction is a powerful technique that allows scientists to amplify a spcific DNA sequence millions of times in just a few hours. The technique was invented by Dr. Kary Mullis in 1983, for which he received the Nobel Prize in chemistry ten years later.

Within a dividing cell DNA replication involves a series of enzyme mediated reactions whose end result is a faithful copy of the entire genome. Enzymes first unwind (denature) the DNA double helix into single strands. Then an RNA polymerase synthesizes a short stretch of RNA complimentary to one of the DNA strands at the start site of replication. This DNA/RNA heteroduplex acts as a priming site for attachment of the DNA polymerase which then produces the complimentary DNA strand.

During PCR, high temperature is used to separate the DNA molecules into separate strands and synthetic sequences of single stranded DNA (20 - 30 nucleotides) serve as primers. Two different primer sequences are used to bracket the target region to be amplified. One primer is complimentary to one DNA strand at the beginning of the target region, a second primer is complimentary to the other strand at the end of the target region.

For more on this topic, click here.