Question

Order the 3 steps of a PCR cycle from the first to last step, starting at the top.

1) Denaturation, Annealing, Extension
2) Annealing, Denaturation, Extension
3) Extension, Denaturation, Annealing

Answer 1

The correct order of the three steps in a PCR cycle is Denaturation, Annealing, and Extension, and this cycle is repeated in the thermal cycler for DNA amplification.

Step-by-step explanation:

The correct order of steps for a cycle of Polymerase Chain Reaction (PCR) from first to last is: Denaturation, Annealing, and Extension. Therefore, option 1 from the choices provided is the correct sequence.

Denaturation: This step involves heating the DNA to approximately 94-96°C to separate the double-stranded DNA into single strands.

Annealing: The temperature is then lowered to around 50-65°C to allow the primers to bind to the single-stranded DNA.

Extension: Finally, the temperature is raised to about 68-72°C, which is optimal for DNA polymerase to synthesize new DNA strands by adding nucleotides to the primers.

This cycle is repeated multiple times in a thermal cycler machine to exponentially amplify the target DNA segment.