Final answer:
The correct order of steps for the PCR procedure is denaturation, annealing, and then extension, which corresponds to the sequence 1, 2, 3. Thus, the answer to the students' question is option 2) 1, 2, 3.
Step-by-step explanation:
The Polymerase Chain Reaction, commonly known as PCR, is a critical technique used in molecular biology to amplify DNA segments. The procedure involves three main steps: denaturation, annealing, and extension. In the first step, denaturation, the DNA double helix is separated into two single strands by heating it to a high temperature (around 94-96°C). During the second step, annealing, the reaction is cooled to allow primers to bind to the complementary sequences on the single-stranded DNA at a lower temperature (around 50-65°C, typically 55°C). In the final step, extension, the temperature is raised again (to about 72°C) to enable a heat-stable DNA polymerase to replicate the DNA, starting from the primers. These steps are repeated through multiple cycles in a PCR machine which is designed to change temperatures quickly and precisely.
According to the provided descriptions, the correct sequence of the PCR steps in chronological order is first denaturation, then annealing, and finally extension. Matching these steps with the numbers given (1 = melting, 2 = annealing, 3 = extension), the correct order is 1, 2, 3. Therefore, the right answer to the question about the correct sequence of PCR procedure steps is option 2) 1, 2, 3.