What are the main steps of polymerase chain reaction (PCR)?

• A. Transcription, translation, and replication.
• B. Denaturation, primer annealing, extension.
• C. Ligation, transformation, deletion.
• D. Denaturation only.

Answer: (B)

PCR amplifies a specific DNA region by cycling through three actions: denaturation, primer annealing, and DNA extension.

First, denaturation separates the double-stranded DNA into single strands by heating. Then, during annealing, short DNA primers bind to complementary sequences flanking the target region when the mixture cools. Finally, extension uses a DNA polymerase to add nucleotides, building new DNA strands from the primers in the 5' to 3' direction. Repeating these steps many times doubles the amount of target DNA with each cycle, producing a large quantity of the specific fragment.

Other options describe processes that aren’t how PCR works (like cellular transcription/translation or other cloning steps) or are incomplete descriptions, so they don’t capture the essential three-step cycle of PCR.