Final answer:
PCR is a molecular biology method used to amplify DNA sequences. It consists of three steps: denaturation, where DNA is heated to become single-stranded; annealing, where primers bind to the template DNA; and extension, where new DNA is synthesized by Taq polymerase.
Step-by-step explanation:
Polymerase Chain Reaction (PCR)
The polymerase chain reaction (PCR) is a method widely used in molecular biology to rapidly make millions to billions of copies of a specific DNA sample, allowing scientists to take a very small sample of DNA and amplify it to a large enough amount to study in detail. PCR consists of three major steps, which are repeated for 30 or 40 cycles. Because this procedure is carried out using a machine that can change temperatures quickly, a large number of DNA copies can be generated in a matter of hours.
The Three Major Steps of PCR
- Denaturation: This is the first step of PCR, where the double-stranded DNA is heated to 94-96°C, causing the hydrogen bonds between the two DNA strands to break and yielding two single strands of DNA.
- Annealing: During this step, the temperature is lowered to about 55-68°C to enable the DNA primers to attach to their complementary sequences on the single-stranded DNA templates.
- Extension: This final step occurs at about 72°C, where Taq polymerase synthesizes a new DNA strand by adding nucleotides to the primed DNA sequences, extending from the primer. It is important to use Taq polymerase in this step because it is resistant to the high temperatures used in PCR.
Repeatedly cycling through these three steps in a PCR machine allows for the exponential replication of the targeted DNA segment.