Final answer:
The steps in the Polymerase Chain Reaction (PCR) are denaturation, annealing, and extension, respectively. These steps are repeated in cycles within a thermal cycler to exponentially copy a specific DNA segment.
Step-by-step explanation:
Steps in the Polymerase Chain Reaction (PCR)
The Polymerase Chain Reaction (PCR) is a widely used technique in molecular biology that makes many copies of a specific DNA segment. The PCR cycle comprises three main steps which are crucial for amplifying the DNA: denaturation, annealing, and extension (also known as DNA synthesis). Each of these steps occurs at varying temperatures within a PCR machine or thermal cycler, specially designed to rapidly change temperatures with precision.
- Denaturation is the step where the double-stranded DNA is heated to approximately 95°C to break the hydrogen bonds between the strands, resulting in two single-stranded DNA molecules.
- Annealing occurs when the temperature is lowered to about 50°C, allowing primers, which are short DNA sequences complementary to targeted sequences on the single-stranded DNA, to attach or 'anneal.'
- Extension involves increasing the temperature to about 72°C, which is the ideal temperature for Taq polymerase to synthesize new DNA strands starting from the primers.
These steps are repeated through multiple cycles to exponentially increase the number of DNA segments that are the same length as the distance between the two primers. Generally, 25-40 cycles are performed to achieve a significant quantity of the targeted DNA fragment.