Polymerase chain reaction (PCR)

Definition

Polymerase chain reaction (PCR) is a technique used to amplify specific DNA sequences, making millions of copies from a small initial sample. It relies on thermal cycling, which involves repeated heating and cooling cycles to denature DNA, anneal primers, and extend new DNA strands.

5 Must Know Facts For Your Next Test

1. PCR requires three main steps: denaturation at high temperature, primer annealing at a lower temperature, and extension at an optimal temperature for DNA polymerase.
2. Taq polymerase, derived from the thermophilic bacterium Thermus aquaticus, is commonly used in PCR because it is stable at high temperatures.
3. Primers are short single-stranded DNA sequences that are complementary to the target region's flanking regions; they guide the starting point for DNA synthesis.
4. PCR can be used for various applications including cloning, gene expression analysis, genotyping, sequencing, and detecting pathogens.
5. The efficiency of PCR can be affected by factors such as primer design, template quality, magnesium ion concentration, and thermal cycler accuracy.

Review Questions

• What are the three main steps of PCR and what happens in each step?
• Why is Taq polymerase often used in PCR instead of other types of DNA polymerases?
• How do primers function in the PCR process?

Related terms

Denaturation:

The process of separating double-stranded DNA into single strands by heating.

Annealing: The binding of primers to their complementary sequences on the single-stranded DNA during PCR.

Extension: The synthesis of new DNA strands by adding nucleotides to the primers during PCR.