STEP IN PCR

Step In Polymerase Chain Reaction (PCR)
EVERYTHING HAPPEN FOR A REASON
How is PCR (polymerase chain reaction) done?

As illustrated in the animated picture of PCR, three major steps are involved in a PCR. These three steps are repeated for 30 or 40 cycles. The cycles are done on an automated cycler, a device which rapidly heats and cools the test tubes containing the reaction mixture. Each step -- denatauration (alteration of structure), annealing (joining), and extension -- takes place at a different temperature:

1. Denaturation: At 94 C (201.2 F), the double-stranded DNA melts and opens into two pieces of single-stranded DNA.
   
2. Annealing: At medium temperatures, around 54 C (129.2 F), the primers pair up (anneal) with the single-stranded "template" (The template is the sequence of DNA to be copied.) On the small length of double-stranded DNA (the joined primer and template), the polymerase attaches and starts copying the template.
   
3. Extension: At 72 C (161.6 F), the polymerase works best, and DNA building blocks complementary to the template are coupled to the primer, making a double stranded DNA molecule.