Describe and explain how the polymerase chain reaction (PCR) is used to amplify a DNA fragment - AQA - A-Level Biology - Question 8 - 2021 - Paper 2

The curve in Figure 9 represents the relationship between the number of PCR cycles and the number of DNA molecules produced. Initially, the rate of increase in DNA molecules is low due to a limited number of nucleotides and primers available for amplification. As the cycles progress, the number of DNA molecules doubles with each cycle, resulting in an exponential increase.

Eventually, the curve plateaus, indicating that the reaction has reached a point where no further amplification occurs. This plateau is due to the depletion of reagents (nucleotides/primers) and the eventual denaturation of the polymerase enzyme used in the reaction, which limits further DNA synthesis.