PCR steps

• Step 1 - MELTING


  DNA is heated to 94°-96°, to separate the DNA strands (by breaking the hydrogen bonds). This stage is called melting.
• Step 2 - ANNEALING 


  DNA is cooled to 50°-65° to allow primers to bind to complementary target sequences at the two ends of the region of DNA to be amplified. This stage is called annealing.
• Step 3 - EXTENDING

  Heat tolerant DNA polymerase adds nucleotides to the primers at the 3' ends of original DNA strands. This is called extending.
• Step 4


  Repeated cycles of heating and cooling amplify the region of DNA. In 1 hour a short length of DNA can become a million.