Polymerase chain reaction (PCR) is a widely used DNA manipulation technique, one with applications in almost every area of modern biology. PCR reactions produce many copies of a target DNA sequence starting from a piece of template DNA. This technique can be used to make many copies of DNA that is present in trace amounts.
Scientists need significant amounts of DNA to study it. Sometimes, only a small piece of DNA is available. Scientists must amplify, or copy, these small pieces to create large amounts of DNA. They do this by using a technique called polymerase chain reaction (PCR). It is a fast and inexpensive way to amplify small pieces of DNA.
What is PCR used for? The DNA produced by PCR can be used in many different laboratory procedures. PCR is used in DNA fingerprinting, or the process of determining a person’s characteristics through their DNA. Itis also helpful in the diagnosis of disorders related to genes and in the detection of bacteria or viruses.
How does it work? The PCR process can be done by a machine in just a few hours. The machine is called a thermocycler. It alters the temperature of the reaction every few minutes. The steps are as follows:
- The machine heats the DNA sample to a high temperature, denaturing the DNA into 2 pieces of single-stranded DNA.
- The machine lowers the temperature, allowing a short stretch of DNA, known as a primer, to bind to the single strands. The primer acts as a signal for the enzyme Taq polymerase.
- The machine raises the temperature again, allowing the Taq polymerase enzyme to synthesize two new strands of DNA using the original strands as templates. This process results in a copy of the original DNA. Each of the new molecules contains 1 old and 1 new strand of DNA. These strands can be used to create two new copies, and so on, and so on.
The cycle of denaturing and synthesizing new DNA is repeated as many as 30 or 40 times. This leads to more than 1 billion exact copies of the original DNA segment.