Polymerase Chain Reaction

• What is the polymerase chain reaction?

  A technique used to amplify one sample of DNA enough times to create a large enough sample for extensive analysis
• What can PCR be used for?

  • Paternity tests
  • Detecting mutations
  • Forensics
• What is needed for PCR?

  • DNA template
  • DNA polymerase
  • DNA nucleotides
  • Primers
  • Thermocycler
• What are primers?

  Short pieces of DNA that bind to the start of each fragment and prevent both ends from joining back up
• What is a thermocycler?

  A computer-controlled machine that varies the temperature of the mixture precisely for set periods
• What is the process of the PCR?

  1. Separation: heat DNA to 95 degrees to break hydrogen bonds
  2. Annealing: Cool to 55 degrees so primers bind and signal polymerase to start synthesising the DNA
  3. Synthesis: Heat to 72 degrees, polymerase forms phosphodiester bonds between nucleotides
• What are the problems with PCR?

  Polymerase can denature due to high temps
• How are the problems overcome?

  The polymerase is sourced from thermophilic bacteria in volcanic vents
• What are the strengths of in vitro?

  • Fast
  • DNA isn't modified
  • Only replicates the fragment of interest
• What are the weaknesses of in vitro?

  • Only replicates small fragments
  • Modified, mRNA and proteins are not made
  • Expensive
• What are the strengths of in vivo?

  • Can be used in gene therapy
  • No risk of contamination
  • 100% accuracy
  • Cuts out specific genes
  • Large quantities