A PCR cycle is a series of three alternating temperature steps – denaturation, annealing, and extension – that are repeated multiple times to amplify a specific DNA region.
Here's a breakdown of each step in a PCR cycle:
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Denaturation: The reaction is heated to a high temperature (typically 94-98°C) to separate the double-stranded DNA template into single strands. This allows the primers to bind in the next step.
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Annealing: The temperature is lowered (typically 50-65°C) to allow the primers to bind (anneal) to their complementary sequences on the single-stranded DNA template. The optimal annealing temperature depends on the primer sequence.
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Extension: The temperature is raised to the optimal temperature for the DNA polymerase enzyme (typically 72°C). The polymerase then extends the primers, synthesizing new DNA strands complementary to the template strands.
This three-step cycle is repeated typically 25-40 times. Each cycle doubles the amount of the target DNA sequence, resulting in exponential amplification. After the cycling is complete, there is often a final extension step to ensure that any remaining single-stranded DNA is fully extended.
In summary, a PCR cycle is the fundamental repeating unit in the polymerase chain reaction (PCR) process that enables the exponential amplification of a specific DNA sequence.
