Question

Which of the following best describes why PCR protocols contain numerous cycles of the denaturation/annealing/extension steps?

1) To amplify the target DNA sequence
2) To increase the sensitivity of the PCR reaction
3) To ensure that all the DNA strands are denatured and annealed properly
4) To allow for the synthesis of multiple copies of the target DNA

Answer 1

PCR cycles are repeated to exponentially amplify a specific DNA sequence, with each cycle involving the separation of DNA strands, primer attachment, and new strand synthesis by DNA polymerase.

Step-by-step explanation:

The Polymerase Chain Reaction (PCR) contains numerous cycles of denaturation, annealing, and extension steps to amplify the target DNA sequence. Each cycle effectively doubles the amount of the target DNA, and since PCR protocols typically include 25-40 cycles, this allows for an exponential increase in the number of copies of the target sequence. During the denaturation step at around 95°C, the double-stranded DNA is separated into single strands. The annealing step, at a lower temperature of approximately 50°C, allows primers to bind to these strands. Lastly, the extension step at 72°C, enables the heat-stable DNA polymerase to add nucleotides to the primers, creating a complementary strand of the target DNA. Repeating these steps results in an exponential amplification of the desired DNA segment, critical for applications such as genetic testing.