Polymerase Chain Reaction (PCR) is a technique for reproducing specific DNA sequences in vitro.
The process is carried out within a machine (see photo), and it can produce millions or billions of copies of a piece of DNA in a few hours.
The sequence of PCR involves the following steps:
A: The DNA to be reproduced is heated to separate the two template strands.
B: Two primers which are complimentary to the region to be amplified are added. A heat-stable DNA polymerase enzyme is also added. The enzyme catalyses the extension of the primers, using the DNA strand as template.
The cycle is repeated, with the newly synthesised double stranded DNA being heat-denatured and the enzymes extending the primers attached to the liberated single DNA strands.
The chain reaction, once set up, results in the exponential amplification of the original DNA, where the number of cycles (n) determines how many copies of the DNA (2n) are produced.
The applications of PCR are extensive, some are:
Amplification of small amounts of DNA for further analysis by DNA fingerprinting.
The analysis of ancient DNA from fossils.
Mapping the human (and other species) genome.
The isolation of a particular gene of interest from a tissue sample.
Detection of microorganisms present in low numbers in soil, food or water.
Here is Joe, a Postgraduate student in Biochemistry at La Trobe, putting a sample into the PCR machine.
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