Diseases, Conditions, Syndromes

Low-cost method for finding new coronavirus variants

Researchers at Karolinska Institutet in Sweden have developed a technology for cost-effective surveillance of the global spread of new SARS-CoV-2 variants. The technique is presented in the scientific journal Nature Communications.

Diseases, Conditions, Syndromes

Is it safe to have surgery after COVID-19 infection?

It is now clear that the lingering effects of COVID-19 can affect your health in many ways—including how your body reacts to surgery. In this case, the changes are significant. A growing number of studies have shown a substantial ...

Diseases, Conditions, Syndromes

COVID-19 PCR tests can be freeze dried

In fighting the COVID-19 pandemic, it's not just the vaccines that require complicated cold supply chains and refrigerated storage. Polymerase chain reaction (PCR) tests—often considered the 'gold standard' of testing—also ...

Diseases, Conditions, Syndromes

Fully vaccinated Canadians can avoid border quarantine soon

Canada's health minister said Wednesday that fully vaccinated Canadian citizens who test negative for COVID-19 will soon be exempt from two weeks quarantine when returning to the country.

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Polymerase chain reaction

In molecular biology, the polymerase chain reaction (PCR) is a technique to amplify a single or few copies of a piece of DNA across several orders of magnitude, generating millions or more copies of a particular DNA sequence. The method relies on thermal cycling, consisting of cycles of repeated heating and cooling of the reaction for DNA melting and enzymatic replication of the DNA. Primers (short DNA fragments) containing sequences complementary to the target region along with a DNA polymerase (after which the method is named) are key components to enable selective and repeated amplification. As PCR progresses, the DNA generated is itself used as a template for replication, setting in motion a chain reaction in which the DNA template is exponentially amplified. PCR can be extensively modified to perform a wide array of genetic manipulations.

Almost all PCR applications employ a heat-stable DNA polymerase, such as Taq polymerase, an enzyme originally isolated from the bacterium Thermus aquaticus. This DNA polymerase enzymatically assembles a new DNA strand from DNA building blocks, the nucleotides, by using single-stranded DNA as a template and DNA oligonucleotides (also called DNA primers), which are required for initiation of DNA synthesis. The vast majority of PCR methods use thermal cycling, i.e., alternately heating and cooling the PCR sample to a defined series of temperature steps. These thermal cycling steps are necessary to physically separate the strands (at high temperatures) in a DNA double helix (DNA melting) used as the template during DNA synthesis (at lower temperatures) by the DNA polymerase to selectively amplify the target DNA. The selectivity of PCR results from the use of primers that are complementary to the DNA region targeted for amplification under specific thermal cycling conditions.

Developed in 1984 by Kary Mullis, PCR is now a common and often indispensable technique used in medical and biological research labs for a variety of applications. These include DNA cloning for sequencing, DNA-based phylogeny, or functional analysis of genes; the diagnosis of hereditary diseases; the identification of genetic fingerprints (used in forensic sciences and paternity testing); and the detection and diagnosis of infectious diseases. In 1993 Mullis was awarded the Nobel Prize in Chemistry for his work on PCR.

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