- PCR stands for “Polymerase Chain Reaction.
- It is a widely used molecular biology technique that allows the rapid amplification of specific DNA segments.
| Year of Discovery | Inventor name | Why called as PCR |
| 1983 | · Polymerase Chain Reaction (PCR) was invented by Kary Mullis. · He was a biochemist working at Cetus Corporation, a biotechnology company. | · The name Polymerase Chain Reaction was given to this technique because it reflects the key process in this technique, where DNA polymerase enzyme is used to amplify specific DNA sequences. |
Biography of Kary Mullis
| Year | Event |
| December 28, 1944 | · Kary Banks Mullis was born in Lenoir, North Carolina, USA. |
| 1979 | · He joined Cetus Corporation (later acquired by Hoffmann-La Roche) as a DNA chemist. |
| 1983 | · Invented the Polymerase Chain Reaction (PCR) technique, which is a revolutionary DNA amplification method. |
| 1986 | · His PCR invention was recognized and published in the scientific journal “Science.” |
| 1993 | · Awarded with the Nobel Prize in Chemistry for his invention of PCR. |
| 1998 | · Mullis published his autobiography “Dancing Naked in the Mind Field,” where he shared insights into his life and scientific journey |
| 2019 | · Kary Mullis passed away on August 7, 2019, in Newport Beach, California, USA, at the age of 74. |
Steps involve in PCR
| Steps | Description |
| Step1. Denaturation | · Heating of the DNA sample to around 94-98°C. · This step separates the two strands of the double-stranded DNA, breaking the hydrogen bonds between them. · The DNA becomes single-stranded. |
| Step2. Annealing | · Cool the sample to around 50-65°C. · DNA primers (short, single-stranded DNA sequences) bind to complementary sequences on each DNA strand. · Primers act as starting points for DNA synthesis in the next step. |
| Step 3. Extension | · Raise the temperature to around 72°C. · A heat-stable DNA polymerase (e.g., Taq polymerase) synthesizes new DNA strands starting from the primers. · The polymerase adds nucleotides to the 3′ end of the primers, extending the DNA strands in the 5′ to 3′ direction. |
| Step 4. Cycling | · Steps 1 to 3 are repeated for multiple cycles (typically 20-40 cycles). · Each cycle doubles the amount of target DNA, resulting in exponential amplification of the desired DNA segment. |
| Step 5. Final Extension | · After the last cycle, the reaction is typically held at 72°C for a short period to ensure completion of any remaining DNA synthesis. · This step helps to ensure that all the DNA strands are fully extended. |
| Step 6. Cooling | The reaction is cooled to a low temperature (e.g., 4°C) for storage or further analysis. The final PCR product, which is a large number of copies of the target DNA, is ready to use. |
Applications of PCR
| Applications | Description |
| DNA Amplification | · PCR allows the rapid and exponential amplification of a specific DNA segment, generating a large number of copies. · It offers excellent specificity, as it amplifies only the targeted DNA sequence with the use of specific primers. |
| Forensic Analysis | · PCR is crucial in forensic analysis, · It helps in the identification of individuals through DNA profiling and evidence examination. |
| Non-Invasive Diagnostics | · In some cases, PCR can diagnose diseases using non-invasive samples like saliva, urine, or blood. |
| Mutation Analysis and Detection | · PCR is used to analyze genetic mutations and screen for specific mutations associated with genetic disorders. |
| Sensitivity and Specificity | · PCR is highly sensitive, capable of detecting minute amounts of target DNA in a complex mixture. |
| Rapid Results | · PCR provides quick results, allowing researchers to obtain DNA amplification within a few hours. |
| Versatility | · PCR has versatile applications, including DNA cloning, gene expression analysis, genetic testing, and diagnostics. |
| Minimal Sample Requirement | · PCR requires only a small amount of DNA as a template, conserving precious or limited samples for further analysis. |
| Identification of Infectious Agents | · PCR aids in identifying infectious agents, such as bacteria and viruses thus helps in the diagnosis of infectious diseases. |
| Monitoring Disease Progression | · PCR allows researchers to track disease progression and treatment response based on changes in target DNA levels. |