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Molecular Pathology

Polymerase Chain Reaction

PCR reaction stages


Author: Rodney E. Shackelford, D.O., Ph.D. (see Reviewers page)

Revised: 22 September 2012, last major update July 2010

Copyright: (c) 2008-2010, PathologyOutlines.com, Inc.




● The thermocycles in PCR can be divided into three stages

● Understanding where each of these stages occurs in each PCR reaction is important, especially for the analysis of end-point PCR reactions


Exponential amplification:

Initially, all the reagents employed (primers and nucleoside triphophates) in PCR are abundant and the Taq polymerase is fully functional

Therefore the initial phases of PCR are characterized by near 100% efficient DNA amplification, with the amount of replicated DNA doubled per thermocycle


Leveling off stage:

In later thermocycles the Taq polymerase begins to lose its activity and the concentration of primers and nucleoside triphophates become rate-limiting, hence the reaction rat significantly slows



Eventually no new DNA amplification occurs due to exhaustion of the reagents and loss of enzyme activity


End of Molecular Pathology > Polymerase Chain Reaction > PCR reaction stages



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