PCRcyklus

PCRcyklus, also known as the Polymerase Chain Reaction cycle, is the fundamental repetitive process at the heart of the Polymerase Chain Reaction (PCR) technique. PCR is a widely used molecular biology method for amplifying specific DNA sequences. Each PCRcyklus consists of three distinct temperature-dependent steps that collectively lead to the exponential replication of target DNA.

The first step is denaturation, typically occurring at a high temperature (around 94-98°C). This heat breaks the hydrogen bonds holding the two strands of the DNA template together, separating them into single strands. These single strands then serve as templates for the subsequent steps.

Following denaturation is annealing, where the temperature is lowered (usually between 50-65°C). At this lower temperature, short DNA sequences called primers bind (anneal) to their complementary sequences on the single-stranded DNA templates. Primers are crucial as they define the specific region of DNA that will be amplified.

The final step is extension or elongation, typically performed at an optimal temperature for the DNA polymerase enzyme (often around 72°C). The DNA polymerase enzyme, a heat-stable enzyme like Taq polymerase, binds to the primer-template complex and begins synthesizing a new DNA strand by adding free nucleotides complementary to the template strand.

These three steps – denaturation, annealing, and extension – constitute one complete PCRcyklus. This cycle is then repeated numerous times, often 20 to 40 times. With each cycle, the number of copies of the target DNA sequence approximately doubles, leading to an exponential amplification of the desired DNA fragment. This process allows for the detection and analysis of even very small amounts of DNA.