What is the principle of PCR?

PCR or Polymerase chain reaction is a technology used for amplifying DNA sequences quickly and easily. It is one of the basic techniques for DNA analysis and is widely used in molecular biology. 

PCR is based on the principle of enzymatic replication of the nucleic acids. The method involves a chain reaction characterized by three distinct steps: 

1. Double-stranded DNA is denatured by increasing the temperature, creating single strands of DNA.
2. DNA is annealed by lowering the temperature, triggering competition between the numerous primers and the two original DNA segments. Primers bind to their complementary sequence on the template strand and serve as the starting point.
3. DNA is then synthesized by a polymerase enzyme. The temperature is increased again as the polymerase attaches to the primer and begins to add complementary base pairs to the template strand creating a new strand of DNA. 

This 3-step cycle is repeated about 25 to 35 times, exponentially duplicating the DNA fragments between the two primers.