By Angelina Chen
What is the Polymerase Chain Reaction (PCR)
The polymerase chain reaction (PCR) or molecular photocopying, is a molecular test, which detects the presence of virus's genetic material (nucleic acids). It is a method widely known to scientists as the synthesis of large amounts of a specific region of the DNA (a molecule that contains the genetic information). Due to this unique detection, PCR can be used to diagnose diseases or viral infections in cells. The reaction is essentially an amplification and multiplication of DNA, where an original strand of DNA is multiplied. This is especially useful as sometimes DNA samples are difficult to analyze. The PCR also helps to better understand DNA structures and the body’s genetic material, due to further magnification. Since PCR is a relatively inexpensive test, it is known and used largely throughout the world, especially to detect viruses such as Covid-19.
Polymerase Chain Reaction Procedure
Materials needed:
Primers: The main focus of the overall synthesis; allows the Taq polymerase (a type of DNA polymerase) to attach the nucleotides for the actual extension of DNA. Primers attach to the DNA sample using complementary base pairing. DNA has four different chemical bases, thymine (T), adenine (A), guanine (G), and cytosine (C). Thymine (T) is complementary to adenine (A), and guanine (G) is complementary to cytosine (C). Primers have to be designed to be complementary to the DNA to allow for accurate replications of the original DNA during the polymerase chain reaction.
DNA polymerases are required for the polymerase chain reaction as this enzyme extends the primer bases to produce new strands of synthesized DNA. PCR requires hot temperatures for the replications of the DNA. The method would require a DNA polymerase which is heat sustainable to be used in the method. The DNA polymerase taken from the bacteria (thermic aquaticus), called taq polymerase, is ideal for the polymerase chain reaction as it is extremely active in high temperatures (thermostable) and is fast.
Nucleotides: The chemical bases of the DNA for the building of new DNA strands.
Template DNA: The strand of DNA to be multiplied for further analysis of it.
Procedure
Step 1: Denaturing
During denaturing, the nucleotides, template (original strand) DNA, taq polymerases, and primers are all placed in a tube. Denaturation is when proteins structures are changed or altered by extreme pressure or stress (heat and acid). In terms of the polymerase chain reaction denaturation is when the two strands of the parent DNA are split apart to allow for the extension of each single strand of DNA. To split the two strands of DNA, which are bound strongly together, scientists would need to heat up the DNA at 95 degrees Celsius, almost at the boiling point.
Step 2: Annealing
The next step of the PCR method is to apply the primers onto the now single strands of DNA, which is known as the process of annealing. The tube which holds the materials together is now cooled down to approximately 60 degrees Celsius (ranges from 55-65 degrees Celsius). The primers attach or bind to the template DNA by complementary base pairing to the specific regions of the DNA that is being amplified.
Step 3: Synthesizing/Extension
The last step of one cycle of replication is the extending the primers. The temperature now increases to 72 degrees Celsius for the Taq polymerases to synthesize the new strands of DNA by extending the primers.
Step 4: Repeat Cycle
Typically, this cycle of PCR is repeated 25-35 times with the process altogether taking around 2 -4 hours. This method allows the original parent DNA to multiply to millions or even billions. Once new DNA is synthesized, the method also uses the new DNA strands as template to synthesize even more strands. Since there are many nucleotides, primers, and polymerases inside the tube, typically each cycle can double the amount of DNA made.
How Has It Helped In Recent Times
The PCR method is widely known for its quick ability to test for multiple antibiotic genes using only one template DNA. It is accurate in terms of detecting virus’s genetic material as it focuses on amplifying specific segments. The polymerase chain reaction is used in many different techniques. This includes the detection of viruses or bacteria in our bodies, the testing of genetic disorders, and DNA fingerprinting (forensics). As mentioned before, the polymerase chain reaction is inexpensive, allowing more scientists to use this method without it being too costly. One large benefit of PCR as of recent times is its use in Covid-19 detection. It was found to be beneficial as even if there was small evidence of the virus, this method was able to detect it.
CONTACT US
Instagram: @synaptoscope