What are the three main steps of the Polymerase Chain Reaction (PCR)?

• A. Polymerase Chain Reaction; transcription, replication, translation.
• B. Polymerase Chain Reaction; denaturation, annealing, extension.
• C. Polymerase Chain Reaction; cloning, sequencing, analysis.
• D. Polymerase Chain Reaction; replication, transcription, translation.

Answer: (B)

PCR amplifies DNA by cycling temperatures through three steps: denaturation, annealing, and extension. Denaturation uses heat to separate the double-stranded DNA into single strands, making the template accessible. Annealing cools the mixture so primers can bind to their complementary sequences on the single strands. Extension raises the temperature to the optimum for DNA polymerase, which then adds nucleotides to the primers and builds new DNA strands, copy by copy. Repeating these steps many times doubles the amount of target DNA with each cycle.

Options that mention transcription, translation, cloning, sequencing, or general replication refer to different cellular processes or later laboratory steps, not the actual PCR cycling steps. Therefore, the correct sequence is denaturation, annealing, extension.