Animal Biotechnology

PCR CYCLES

•  PCR involves a repetitive series of temperature cycles. Each reaction cycle comprises of three stages
  • Denaturation
  • Primer annealing and
  • Extension.
• In the first cycle, the target DNA is separated into two strands by heating to 95^ºC- denaturation.
• The temperature is reduced to around 55^ºC to allow the primers to anneal. The actual temperature depends on the primer lengths and sequences- primer annealing.
• After annealing, the temperature is increased to 72^ºC for optimal polymerization which uses up dNTPs in the reaction mix and requires Mg2+.
• If PCR was 100% efficient, one target molecule would become 2n after ‘n’ cycles. In practice, 20- 40 cycles are commonly used.