January 16, 2023
#ABC of lab

PCR is shorthand for a simple but very useful procedure in molecular biology called the polymerase chain reaction. It is a technique used to amplify a segment of DNA of interest or produce lots and lots of copies. In other words, PCR enables you to produce millions of copies of a specific DNA sequence from an initially small sample – sometimes even a single copy. It is a crucial process for a range of genetic technologies and, in fact, has enabled the development of a suite of new technologies.

PCR is a common tool used in medical and biological research labs. It is used in the early stages of processing DNA for sequencing, for detecting the presence or absence of a gene to help identify pathogens during infection, and when generating forensic DNA profiles from tiny samples of DNA.

How does PCR works

PCR mimics what happens in cells when DNA is copied (replicated) prior to cell division, but it is carried out in controlled conditions in a laboratory. The machine that is used is simply called a PCR machine or a thermocycler. Test tubes containing the DNA mixture of interest are put into the machine, and the machine changes the temperature to suit each step of the process.

What is the PCR process?

Denaturing : when the double-stranded template DNA is heated to separate it into two single strands.

Annealing: when the temperature is lowered to enable the DNA primers to attach to the template DNA.

Extending: when the temperature is raised and the new strand of DNA is made by the Taq polymerase enzyme.

The result of one cycle of PCR is two double-stranded sequences of target DNA, each containing one newly made strand and one original strand.

The cycle is repeated many times (usually 20–30) as most processes using PCR need large quantities of DNA. It only takes 2–3 hours to get a billion or so copies.

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