Question

PCR is used to amplify DNA fragments. The reaction is heated to 95 degrees C and then cooled to 55 degrees C. Immediately upon cooling, what happens?

a) Annealing of primers to the target DNA
b) DNA denaturation
c) DNA elongation by DNA polymerase
d) Activation of Taq polymerase

Answer 1

In PCR, the annealing of primers to the target DNA occurs immediately upon cooling the reaction.

Step-by-step explanation:

The correct answer is option a) Annealing of primers to the target DNA immediately upon cooling.

In PCR, the first step is denaturation, where the DNA template is heated to approximately 95°C to separate the strands. Next, during the annealing step, the temperature is cooled to approximately 55°C. At this temperature, the primers, which are short DNA sequences that are complementary to the target DNA, anneal or bind to the template strands. The primers provide a starting point for DNA polymerase to bind and initiate DNA synthesis.

So, immediately upon cooling, the annealing of primers to the target DNA occurs in the PCR reaction.