Polymerase Chain Reaction (PCR)

What is PCR?

Polymerase Chain Reaction (PCR) is a rapid laboratory technique that produces billions of copies of specific DNA segments, greatly impacting molecular biology. PCR allows scientists to amplify DNA sequences for applications like genotyping and gene expression analysis. The technique relies on DNA polymerase, an enzyme that assembles DNA strands.

Developed by Kary Mullis in the 1980s, PCR earned him the Nobel Prize in Chemistry in 1993. Mullis used two primers, short segments of DNA or RNA that bind to the DNA section of interest, to initiate the process. Although PCR was initially manual and tedious, technological advancements led to the industrialization of PCR with programmable thermal cyclers.

The PCR process requires five core components: a DNA template, primers, nucleotide bases (adenine [A], thymine [T], guanine [G], and cytosine [C]), Taq polymerase (which synthesizes new DNA), and a buffer. 

PCR consists of three main phases. In the denaturing phase, the mixture is heated to 94-95°C, causing the DNA strands to separate. The annealing phase cools the mixture to 50-65°C, allowing the primers to attach to the single-stranded DNA. Finally, in the extending phase, the temperature is raised to 72°C, where Taq polymerase synthesizes the new DNA strands by adding nucleotides in the 5' to 3' direction, creating double-stranded DNA molecules. This step typically takes about one minute to copy 1,000 bases.

How can PCR be utilized?

PCR is broadly utilized to address emerging global threats, particularly COVID-19 during the pandemic. The PCR test analyzes upper respiratory samples to detect the RNA of SARS-CoV-2, the virus responsible for the disease. This method amplifies small quantities of RNA into DNA, enabling detection if the virus is present. Authorized for use in the U.S. in February 2020, PCR has become the gold standard for diagnosing COVID-19.

Additionally, PCR proves effective in identifying food-borne pathogens, such as Cyclospora Cayetanensis, linked to illnesses caused by contaminated vegetables. Although a detection method was initially developed in 2004, recent U.S. Food and Drug Administration advancements have significantly enhanced sensitivity and specificity. The updated approach involves washing produce, extracting DNA, and amplifying it with PCR to identify contamination in various foods, including cilantro and lettuce. Today, PCR plays a vital role in next-generation sequencing and other diagnostic techniques, including point-of-care testing for diseases like Bacillus anthracis and HIV across different regions.

Moreover, the range of syndromic PCR testing is expected to expand in the future. “In the next decade, multiplex testing based on PCR technology is expected to become more sophisticated and efficient, through the advancements in automation systems,” explains Jik-Young Park, vice president of Seegene’s R&D Division.

Works Cited

“A brighter future with advances in PCR.” Seegene, nature research custom media, https://www.nature.com/articles/d42473-024-00261-6#:~:text=%E2%80%9CIn%20the%20next%20decade%2C%20multiplex,automation%20system%2C%E2%80%9D%20says%20Park.&text=Another%20area%20that%20PCR%20is,in%20blood%20and%20urine%20samples. Accessed 20 December 2024.

“Polymerase Chain Reaction (PCR).” NCBI, 9 November 2017, https://www.ncbi.nlm.nih.gov/probe/docs/techpcr/. Accessed 20 December 2024.

“Polymerase Chain Reaction (PCR).” National Human Genome Research Institute, https://www.genome.gov/genetics-glossary/Polymerase-Chain-Reaction-PCR. Accessed 20 December 2024.

Schmerker, Jeff. “The History of PCR and importance for genomic research.” Integrated DNA Technologies, 12 January 2022, https://www.idtdna.com/pages/community/blog/post/pcr-its-history-and-importance-for-genomic-research. Accessed 20 December 2024.

“The History of PCR.” Thermo Fisher Scientific, https://www.thermofisher.com/us/en/home/brands/thermo-scientific/molecular-biology/molecular-biology-learning-center/molecular-biology-resource-library/spotlight-articles/history-pcr.html. Accessed 20 December 2024.

“What is PCR (polymerase chain reaction)?” Your Genome, https://www.yourgenome.org/theme/what-is-pcr-polymerase-chain-reaction/. Accessed 20 December 2024.