What is PCR amplification cycle and the purpose of each step?

• A. Denaturation separates strands; annealing primers bind; extension creates the new DNA strand.
• B. Denaturation binds primers; annealing extends; extension separates strands.
• C. Extension occurs to extend the new DNA strand; the cycle is repeated to amplify.
• D. PCR uses RNA as template and amplifies proteins.

Answer: (C)

PCR cycles rely on three key steps repeated many times to amplify a target DNA region. First, denaturation uses heat to separate the double-stranded DNA into two single strands. Then, annealing lowers the temperature so short DNA primers can bind to their complementary sequences flanking the target region. Finally, extension uses a DNA polymerase to add nucleotides and build new DNA strands starting from the primers. Each complete cycle doubles the amount of target DNA, leading to exponential amplification as the process is repeated.

The option that mentions only extension and says the cycle is repeated to amplify misses the essential denaturation and annealing steps, so it doesn’t describe how primers gain access to the target and how the DNA strands are separated for synthesis. Other statements that claim denaturation binds primers, or that PCR uses RNA templates to amplify proteins, are not correct descriptions of how PCR works.