Polymerase Chain Reaction (PCR)

What is PCR?: Genetic Technology used the replicate a target sequence of DNA quickly, and to make a lot of copies. It is DNA replication, but in a laboratory done by humans.

It takes place in three steps:

• Step one: Denaturation

  • Double-stranded DNA separated into 2 single strands

  • Heated at 94-96° C for 20-40s to break hydrogen bonds holding strands together

• Step two: Annealing

  • 50 to 65°C for 20-40 s

  • DNA primers are synthesized

  • Attached to the single strands from at 3' end

  • Targets a small part of a larger DNA strand

• Step three: Elongation

  • Two new DNA strands synthesized at 72°C

  • DNA polymerase attaches to the primer-template hybrids, and moves along, adding nucleotides

  • Taq polymerase is needed for elongation, because it can withstand high temperatures

Results:

After all three steps are done, there are two double-stranded DNA, which are denatured and the process begins again. After three cycles, there are two molecules that match the target sequence exactly, without extra DNA. After twenty cycles, there are over one million copies of the DNA sequence.

Uses:

• Genome mapping

  • Used in the Human Genome Project

• DNA fingerprinting

• Detection of bacteria and viruses

  • AIDS

• Diagnosis of genetic disorders