Section 4 Lesson 3 – PCR

1. Section 4Lesson 3– PCR

2. PCR – The Polymerase Chain Reaction PCR is a technique used to amplify specific sequences of DNA. This technique can be used to create up to millions of copies of a single sequence. The process was developed in 1983 and is now used routinely for many purposes including: DNA Sequencing Genetic Fingerprinting Diagnosis of Hereditary Diseases Diagnosis of Infectious Diseases Phylogeny

3. How Does it Work?

5. PCR Cycle In order to generate many copies, the denature and synthesis steps need to be repeated between 20 and 40 times. Each time there is a doubling of the number of copies. PCR Video PCR Animation

6. Step 1 - Denaturing Denaturing – in this context it means that the DNA is unwinding and the 2 strands are separating from each other. This normally occurs between 90 and 100˚C. The weaker hydrogen bonds are broken while the stronger covalent bonds of the DNA remain intact.

7. Step 2 - Annealing Annealing – this refers to the ‘sticking’ of the primers to the DNA with hydrogen bonds. The primers mark the ends of the target sequence. Target sequences are normally 100-600 bases long while primers are normally 20-30 bases long. Annealing occurs at a temperature of 40 – 60˚C.

8. Step 3 - Extension A DNA polymerase called Taqthen makes a copy of the DNA. Taq is a very special thermostable DNA polymerase that can operate at 72˚C. Taq synthesises from the 3’ end only.

9. Fun with PCR Bioradpcr

10. Your Tasks Add the red terms to your glossary. Make an A4 poster showing the stages of PCR and the uses of PCR. Include the important temperatures.