During which phase does DNA strands separate in PCR?

• A. Extension
• B. Annealing
• C. Denaturation
• D. Finalization

Answer: (C)

In the Polymerase Chain Reaction (PCR), the DNA strands separate during the denaturation phase. This phase is characterized by the application of heat, typically to a temperature around 94-98 degrees Celsius. The high temperature disrupts the hydrogen bonds that hold the two strands of the DNA double helix together, causing the strands to separate and become single-stranded DNA. This step is crucial as it prepares the DNA templates for the subsequent annealing phase, where primers can bind to the single-stranded DNA to initiate the replication process. Understanding the timing and purpose of each PCR phase, especially denaturation, is essential for successful amplification of the target DNA sequence.