Principles and medical applications of the polymerase chain reaction

Abstract

The polymerase chain reaction (PCR) is currently one of the mainstays of medical molecular biology. One of the reasons for the wide adoption of PCR is the elegant simplicity of the way in which the reaction proceeds and the relative ease of the practical manipulation steps. Indeed, combined with the relevant bioinformatics resources for the practical design and for the determination of the required experimental conditions, it provides a rapid means for DNA diagnostic identification and analysis. It has also opened up the investigation of cellular and molecular processes to those outside the field of molecular biology and also contributed in part to the successful sequencing of the human genome project. Polymerase chain reaction is an in vitro amplification method able to generate a relatively large quantity (about 105 copies, or approx 0.25-0.5 g) of a specific DNA sequence from a small amount of a heterogeneous DNA target, often comprising the total cellular genome. The sensitivity of PCR is such that successful amplification can be achieved from a single cell, as in single-sperm typing and preimplantation diagnosis, or from a minority DNA population that is present among an excess of background DNA (e.g., from viruses infecting only a few cells, or from low levels of "leaky" RNA transcription from nonexpressing tissues). The PCR process consists of incubating a reaction sample containing the DNA substrate and required reactants repeatedly between three different temperature incubations: denaturation, annealing, and extension. Many current investigators, the author included, recall their initial introduction to PCR as comprising the laborious transfer of sample tubes between three water baths heated to different temperatures representing the three incubations. Fortunately and no doubt instrumental to the wide implementation of PCR in numerous areas of fundamental research and applications is the automation of the process. This was the result of the development of programmable thermal cylcers that were developed only a few years subsequent to the invention of PCR by Mullis in 1983. Today, the technology has advanced to modern thermal cyclers that use Peltier heating and cooling elements to produce fast temperature changes or ramp rates ofaround 3°C/s and that maintain accurate temperature control across the entire sample block. In addition PCR undertaken in 96-well microtiter plate systems is now possible, which is useful for high-Throughput analysis of clinical samples. © 2008 Humana Press.