The three steps of PCR (Polymerase Chain Reaction) are denaturation, annealing, and extension.
These three steps form a cycle, which is repeated multiple times to amplify a specific DNA sequence. Here's a more detailed explanation of each step:
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Denaturation: This is the first step, where the double-stranded DNA template is heated to a high temperature (typically 94-98°C). This heat breaks the hydrogen bonds holding the two DNA strands together, separating them into single strands. Think of it as unzipping a zipper.
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Annealing: In this step, the temperature is lowered (typically 50-65°C) to allow the primers to bind to the single-stranded DNA template. Primers are short, single-stranded DNA sequences that are complementary to the regions flanking the target DNA sequence you want to amplify. The primers essentially mark the beginning and end of the DNA segment to be copied.
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Extension: During this final step, the temperature is raised to the optimal temperature for the DNA polymerase enzyme (typically 72°C). DNA polymerase then binds to the primers and begins adding nucleotides to the 3' end of each primer, extending the new DNA strand complementary to the template. This results in the creation of two new double-stranded DNA molecules.
The entire cycle (denaturation, annealing, and extension) is repeated typically 25-35 times, leading to an exponential amplification of the target DNA sequence. Each cycle doubles the amount of DNA, so after 30 cycles, you can have over a billion copies of the target sequence.
