Jun 12, 2018 · PCR (polymerase chain reaction) is a method to analyze a short sequence of DNA (or RNA) even in samples containing only minute quantities of DNA or RNA. PCR is used to reproduce (amplify) selected sections of DNA or RNA. Previously, amplification of DNA involved cloning the segments of interest into vectors for expression in bacteria, and took ... Mar 22, 2012 · In our bodies, each polymerase has a special job, but in PCR you only need a single polymerase that can use the primers and the sequences put into the reaction. Topoisomerase helps to unwind the DNA double helix, but since PCR only uses de-annealed DNA (it de-anneals because of the heat) and primers, there is no double helix to unwind.

No known DNA polymerase is able to begin a new chain (de novo); it can only add a nucleotide onto a pre-existing 3'-OH group, and therefore needs a primer at which it can add the first nucleotide. Primers consist of RNA or DNA bases (or both).