The first step in PCR involves raising the temperature of the sample enough to break the hydrogen bonds in DNA to allow access to template strand of DNA for translation but the temperature is not too high to permanently damage the DNA. This is usually about 94 degrees Celsius. 

Step One: Denaturation

This step involves the annealing of the primers to the DNA to allow for translation from the DNA polymerase in the last step. This is a lower temperature around 50 degrees Celsius. 

Step Two: Annealing

During the extension step of the Polymerase Chain Reaction (PCR), the temperature is raised to approximately 74 degrees Celsius. This specific temperature allows the DNA polymerase enzyme to activate and synthesize a new DNA strand in the solution.

Polymerase Chain Reaction (PCR) - Step 3: Extension

There are three broad steps of PCR
- Denaturation 
- Annealing
- Extension 

These steps are repeated as many times as desired to keep synthesizing the DNA fragment desired. 

Grand Valley State University

Polymerase chain reaction (PCR) was discovered in 1985. It is technique usedin laboratories that allows for the synthesis of a lot of a specific fragment of DNA 

Polyermase Chain Reaction (PCR)

Garibyan, L., & Avashia, N. (2013). Polymerase chain reaction. The Journal of investigative dermatology, 133(3), 1–4. 

Polymerase Chain Reaction

PCR has been used to diagnose diseases, identify a perpetrator in a crime scene by matching the DNA at a crime scene with suspects, clone genes, and sequence genes. 

Applications of PCR

- PCR is very sensitive – any impurities in the DNA sample can cause errors in the results. 

- Although the PCR primers are designed to be specific to the DNA fragment of interest, they can anneal to pieces of DNA which will cause the PCR to amplify wrong pieces of DNA. Thus, great care must be taken to not contaminate the samples.  


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