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The polymerase chain reaction (PCR). Prior knowledge. The structure of DNA. DNA replication process. What is PCR?. PCR (Polymerase chain reaction) was developed by Kary Mullis in the mid-1980s. For which he received the Nobel Prize. It has revolutionized molecular biology. What is PCR?.

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Prior knowledge
Prior knowledge

  • The structure of DNA.

  • DNA replication process.


What is pcr
What is PCR?

PCR (Polymerase chain reaction) was developed by Kary Mullis in the mid-1980s.

For which he received the Nobel Prize.

It has revolutionized molecular biology.


What is pcr1
What is PCR?

PCR allows specific sections of DNA to be amplified in vitro (replicated out with a cell in a test tube (in vitro = in glass)).



The first cycle in a few hours in a thermocycler.

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Single copy of DNA

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Step 1: The DNA is heated at approx. 95 oC for a few seconds. This causes the DNA to denature and the strands to separate.


5 in a few hours in a thermocycler.’

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PCR primer

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Step 2: The DNA is cooled to approx. 50-65 oC for a few seconds. This makes short primers to bond to the separated DNA strands.


5 in a few hours in a thermocycler.’

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Step 3: The DNA is heated again to approx. 72oC for a few minutes. This allows a heat-tolerant DNA polymerase to replicate the DNA.

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Step 4: Heat the DNA up to 95 oC again.

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Step 5: Cool to between 50 – 65 oC again. The primers now bond to the original fragments and the copies.

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Step 6: Heat to 72 oC again. The DNA polymerase copies the DNA again. The process is copied over and over again for roughly 20-30 cycles.


Requirements for pcr
Requirements for PCR in a few hours in a thermocycler.

Sequence specific primers – these are designed by the scientist and can be manufactured by a machine.

The sequence for primers can be designed by looking at the published genome sequences.


  • Primers in a few hours in a thermocycler.

  • Supply of nucleotides

  • pH buffer

  • Mg2+ - DNA polymerase co-factor (makes the polymerase work better)


Uses of pcr
Uses of PCR in a few hours in a thermocycler.

  • DNA Profiling

    PCR helps to rapidly identify people. Specific areas of DNA known to vary between individuals is amplified. Giving different sized fragments in different people.


2. in a few hours in a thermocycler.Disease detection

DNA sequences that are known to indicate certain genetic disorders or diseases are amplified using PCR for the purposes of diagnosis.


3. in a few hours in a thermocycler.Archeological analysis

Ancient DNA, degraded over the years, can be amplified and used in archaeological, paleontological and evolutionary research.


5. in a few hours in a thermocycler.Population studiesAnalysis of human or other species’ population genetics can be rapidly performed using PCR analysis.

6. Sequencing DNA sequences can be worked out.


Key concepts
Key concepts in a few hours in a thermocycler.

  • Small sections of DNA can be replicated in vitro using the PCR.

  • PCR manipulates the natural process of DNA replication.

  • PCR is now an automated technique widely used in many areas of research and industry.

  • PCR requires template DNA, Taq polymerase, di-deoxynucleic acids with each of the four DNA bases, Mg2+, primers and a buffer.

  • PCR involves continuous and repeated cycles of heating and cooling.


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