PCR (polymerase chain reaction)

PCR (polymerase chain reaction)
Name	PCR (polymerase chain reaction)
Inventor	Kary Mullis
Year	1983
Field	Molecular biology
Components	DNA template, primers, nucleotides, DNA polymerase

PCR (polymerase chain reaction) is a laboratory technique used to amplify specific DNA sequences exponentially using thermal cycling and a DNA polymerase. Developed in the 1980s, it revolutionized molecular genetics, clinical diagnostics, forensic science, and biotechnology by enabling rapid replication of target loci from minute samples. PCR underpins contemporary work in genomics, epidemiology, and evolutionary biology, linking institutions and events in modern molecular research.

Overview

PCR amplifies defined segments of deoxyribonucleic acid using repeated cycles of denaturation, annealing, and extension to produce millions to billions of copies of a target region. The method relies on synthetic oligonucleotide primers designed to flank the locus of interest and a thermally stable DNA polymerase to synthesize complementary strands, and it is implemented on thermal cyclers used in laboratories associated with National Institutes of Health, Centers for Disease Control and Prevention, World Health Organization, Harvard University, and Stanford University. PCR enabled technological advances exploited by projects like the Human Genome Project, clinical programs at Mayo Clinic, and diagnostic platforms at Roche Diagnostics.

History and development

The conceptual and practical development of PCR is linked to researchers and institutions active in late 20th-century molecular biology, including work in laboratories at Cetus Corporation and the independent efforts of individuals associated with University of California, Berkeley and Scripps Research. The invention was recognized by awards such as the Nobel Prize in Chemistry given to its inventor, and commercialization involved companies like Thermo Fisher Scientific and Bio-Rad Laboratories. Early applications connected PCR to initiatives at Cold Spring Harbor Laboratory, population studies conducted by scholars linked to Smithsonian Institution, and public health responses coordinated with agencies including European Centre for Disease Prevention and Control and Public Health England.

Principles and methodology

PCR is performed by cycling through temperature stages: high-temperature denaturation to separate DNA strands, lower-temperature annealing for primer binding, and an intermediate-temperature extension for polymerase activity. Key reagents include template DNA often prepared in facilities like Johns Hopkins University clinical labs, forward and reverse primers synthesized by companies such as Integrated DNA Technologies, deoxynucleotide triphosphates supplied by vendors like Sigma-Aldrich, and thermostable polymerases derived from organisms studied at institutions like University of Wisconsin–Madison and University of Illinois Urbana-Champaign. Instrumentation includes programmable thermal cyclers from firms such as Eppendorf and Agilent Technologies used broadly in environments from National Cancer Institute research centers to university teaching laboratories at Massachusetts Institute of Technology.

Protocol design balances primer melting temperatures, magnesium ion concentration, and cycle number; quantitative variants incorporate fluorescent probes and detection systems supplied by corporations like Illumina and Applied Biosystems. Standard workflows are taught at training sites including Cold Spring Harbor Laboratory courses and methodological compendia published by publishers associated with Nature Publishing Group and Elsevier.

Variants and specialized techniques

Numerous adaptations extend PCR utility: reverse transcription PCR integrates reverse transcriptase enzymes used in virology research at Centers for Disease Control and Prevention and Pasteur Institute; real-time PCR (qPCR) couples amplification to fluorescence detection applied in laboratories at Fred Hutchinson Cancer Center and Karolinska Institutet; digital PCR partitions samples for absolute quantification used by diagnostic companies like Bio-Rad Laboratories and Stilla Technologies. Multiplex PCR assays detect multiple targets simultaneously in clinical settings such as Cleveland Clinic and Guy's and St Thomas' NHS Foundation Trust. Long-range PCR, touchdown PCR, and hot-start PCR are specialized methods utilized by genome centers like Wellcome Sanger Institute and consortia such as the 1000 Genomes Project.

Applications

PCR is fundamental in genetic testing, infectious disease diagnostics, forensic identification, ancient DNA analysis, and research. Clinical applications include pathogen detection in outbreaks managed by World Health Organization and Centers for Disease Control and Prevention, oncogene detection in oncology centers like Memorial Sloan Kettering Cancer Center, and pharmacogenetic screening implemented at facilities such as Mayo Clinic. Forensics employs PCR in casework processed by agencies like FBI laboratories and national police forensic units in countries including United Kingdom and Germany. In conservation biology and paleogenomics, PCR supports studies by teams affiliated with Smithsonian Institution, Natural History Museum, London, and researchers involved in projects at Max Planck Institute for Evolutionary Anthropology.

Limitations, errors, and contamination control

PCR is susceptible to inhibition by sample contaminants encountered in clinical settings at Veterans Health Administration hospitals and environmental samples processed by US Geological Survey. Errors arise from mispriming, polymerase infidelity, and carryover contamination; high-fidelity enzymes developed by firms like New England Biolabs reduce sequence errors for applications at genome centers such as Broad Institute. Contamination control strategies include physical separation of pre- and post-amplification areas in laboratory networks like those at National Institutes of Health, use of uracil-DNA glycosylase workflows adopted in clinical labs at Johns Hopkins University Hospital, and workflow validation practices promoted by agencies including Food and Drug Administration and European Medicines Agency.

Ethical, legal, and safety considerations

PCR-driven capabilities raise ethical and legal issues in areas such as genetic privacy adjudicated by laws and institutions including European Court of Human Rights and United States Supreme Court, forensic databasing policies overseen by agencies like Interpol and national legislatures, and clinical testing regulation by Food and Drug Administration and National Health Service. Biosafety practices for PCR work are governed by guidelines from organizations such as World Health Organization, Centers for Disease Control and Prevention, and institutional biosafety committees at research universities including Yale University and University of Cambridge to mitigate risks associated with handling infectious material and recombinant DNA.

Category:Molecular biology