How does PCR differ from DNA replication in a cell?

• A. It uses heat to separate DNA strands
• B. It copies whole chromosomes only
• C. It requires no primers
• D. It uses RNA as template

Answer: (A)

PCR differs from DNA replication in how the double-stranded DNA is unwound. In a living cell, replication relies on helicase to unzip the DNA and a suite of enzymes to manage topology, primer placement, and continuous synthesis of new strands at replication forks. In PCR, the DNA strands are separated by heat in a rapid denaturation step, which makes single-stranded templates that primers can bind to during the next steps. The reaction uses short DNA primers designed to flank the target region and a heat-stable DNA polymerase to extend from those primers, cycling through denaturation, annealing, and extension to amplify a specific fragment exponentially. This targeted amplification is different from cellular replication, which copies entire genomes under tightly regulated control.