[Saltar al contenido](https://www.sigmaaldrich.com#main-content) [](https://www.sigmaaldrich.com/ES/es) Productos Carrito0 ESES Productos [Inicio de sesión / Registrarse](https://www.sigmaaldrich.com/oidc-sign-in) [Búsqueda de pedido](https://www.sigmaaldrich.com/ES/es/order-lookup) [Pedido rápido](https://www.sigmaaldrich.com/ES/es/quick-order) Carrito0 [Home](https://www.sigmaaldrich.com/ES/en)[Polymerase Chain Reaction Applications](https://www.sigmaaldrich.com/ES/en/applications/genomics/pcr)Polymerase Chain Reaction (PCR) Basics # Polymerase Chain Reaction (PCR) Basics ## What is PCR? Polymerase chain reaction (PCR) is a common molecular biology technique that enables researchers to make multiple copies of a specific region of DNA. PCR is efficient, rapid and can amplify DNA or RNA sequences from various sources. Once the DNA has been sufficiently amplified, the resulting product can be sequenced, analyzed by gel electrophoresis, or cloned into a plasmid for experimental purposes. ## How does PCR work? What are the steps of PCR? A simple PCR reaction consists of target DNA, a set of synthetic oligonucleotide primers that flank the target DNA sequence, a thermostable DNA polymerase (usually *Taq* polymerase), and nucleotides. The three steps to each amplification cycle include denaturation, annealing and extension. 1. Firstly, the DNA is denatured by heating to 90-95 ˚C, which separtates double-stranded DNA (dsDNA) to single-stranded DNA. The temperature at which 50% of the dsDNA is denatured is known as the melting temperature (Tm) and is determined by the G+C content, the length of the sample, and the concentration of ions (primarily Mg2+). 2. During the annealing step, the sample is cooled to 40-60 ˚C, allowing the primers to attach to the target DNA. 3. The final PCR step occurs at 70-75 ˚C and is known as extension. During this stage, DNA polymerase extends the DNA from the primers, creating new dsDNA with one old strand and one new strand. ## What are PCR primers? Primers are single strands of nucleic acids (synthetic oligonucleotides) that are necessary to initiate the PCR. These single strands of DNA or RNA are specific and complementary to the target DNA/RNA sequence portion. During the cooling (annealing) phase of PCR, the primer binds to the target and initiates copying of the target DNA/RNA sequence. Primers are used in pairs, known as forward and reverse primers. We offer [custom oligos](https://www.sigmaaldrich.com/ES/en/product/sigma/oligo) in multiple formats. Primer sequences must be chosen to target a unique region of DNA, avoiding the possibility of hybridization to a similar sequence. When designing primers, the pairs should have similar melting temperatures because the annealing step occurs for both strands simultaneously. Furthermore, a primer with a *T*m (melting temperature) too much higher than the reaction's annealing temperature could hybridize and extend at an undesired DNA sequence. A *T*m much lower than the annealing temperature could result in failure to anneal. ## How many copies of DNA does PCR generate? Because the strands synthesized in one PCR cycle serve as a template in the next cycle, a million-fold increase in the amount of DNA is achieved in just 20 cycles. These cycles can be performed automatically using a thermal cycler instrument.1,2,3 ## Popular PCR Products Routine PCR is used to produce an amplified amount of DNA for downstream applications, including clone length verification. Our products offer a variety of options to perform routine PCR. Our ReadyMix™ PCR reaction mixes and REDTaq® dye options provide an added convenience for your amplification reaction. - Taq DNA Polymerases - PCR Reaction Mixes - Roche AptaTaq Fast Start DNA Polymerase - Roche Expand™ - Roche *FastStart™ Taq* ## [](https://www.sigmaaldrich.com)Taq DNA Polymerases *Taq* DNA polymerase is a specialized thermostable enzyme isolated from *Thermus aquaticus,* a thermophillic bacterium. *Taq* is the most commonly used DNA polymerase for PCR and is now expressed recombinantly in *E. coli*. The enzyme is capable of 5′ → 3′ polymerase and exonuclease activity; SDS-PAGE examination finds no detectable contamination associated with endonucleases or exonucleases. | | | | |-----------------------------------------------------------------|-----------------------------------------------------------|-----------------------------------| | Product No. | Product Name | Features | | [D1806](https://www.sigmaaldrich.com/ES/en/product/SIGMA/D1806) | Taq DNA Polymerase with 10X Reaction Buffer | • Buffer optimized with MgCl2 | | [D4545](https://www.sigmaaldrich.com/ES/en/product/SIGMA/D4545) | Taq DNA Polymerase with 10X Reaction Buffer without MgCl2 | • Separate vial of MgCl2 provided | Table 1. ### REDTaq® DNA Polymerases REDTaq® DNA Polymerase is our unique blend of *Taq* DNA polymerase with an inert red dye. This blend performs as well as a clear *Taq* enzyme blend and does not interfere with downstream applications. Its primary function is identification – solutions are easy to keep track of in PCR tubes and gels. If necessary, the dye can be removed by standard purification methods post amplification.  __Figure 1.__The REDTaq® DNA Polymerase yield compared to standard Taq under identical conditions.  __Figure 2.__The REDTaq® dye migrates like a 125 bp fragment so there is no need for loading buffers and tracking dyes. Product No.Product NameFeatures [D4309](https://www.sigmaaldrich.com/ES/en/product/SIGMA/D4309)REDTaq® DNA Polymerase• Buffer optimized with MgCl2 [D8312](https://www.sigmaaldrich.com/ES/en/product/SIGMA/D8312)REDTaq® Genomic DNA Polymerase• For Genomic DNA amplification • Includes 10X buffer optimized with MgCl2 [D2812](https://www.sigmaaldrich.com/ES/en/product/SIGMA/D2812)REDTaq® Genomic DNA Polymerase without MgCl2• For Genomic DNA amplification • Includes 10X buffer and separate vial of MgCl2 [D6063](https://www.sigmaaldrich.com/ES/en/product/SIGMA/D6063)REDTaq® SuperPak™ DNA Polymerase• High visibility polymerase for Genomic DNA • Includes dNTPs and 10X MgCl2 optimized PCR buffer Table 2. ## PCR Reaction Mixes The ReadyMix™ PCR reaction mixes contain our high-quality *Taq* DNA polymerase, 99% pure dNTPs, and buffer in a 2X optimized reaction concentrate. This convenient product reduces pipetting and minimizes the risk of contamination by eliminating various mixing steps. Simply add template and primers to the ReadyMix™ Reaction Mix. PCR reaction mixes are formulated to address various PCR needs and can be purchased in combination with REDTaq® Dye for additional convenience.  __Figure 3.__Amplification of 1, 2, 3, and 7 kb fragments and a 4.5 kb human genomic DNA using the ReadyMix™ Taq PCR Reaction Mix. Product No.Product NameFeatures R2523REDTaq® ReadyMix PCR Reaction Mix• Includes *Taq* DNA polymerase, 99% pure deoxynucleotides, and reaction buffer in a 2× optimized reaction concentrate • Includes REDTaq dye for identification P4600ReadyMix™ *Taq* PCR Reaction Mix• Includes *Taq* DNA Polymerase, 99% pure deoxynucleotides and buffer in a 2× optimized reaction concentrate Table 3. Lo sentimos, se ha producido un error inesperado Response not successful: Received status code 500 ### References 1\. Innis M. A. 2012. PCR protocols: a guide to methods and applications.. Academic press. 2\. Haynie DT. 2001. Biological Thermodynamics. [https://doi.org/10.1017/cbo9780511754784](https://doi.org/10.1017/cbo9780511754784) 3\. McPherson, Mike, Simon M. 2000. PCR. London: Taylor & Francis. __Related Articles__ - [Extract-N-Amp™ Product Guide](https://www.sigmaaldrich.com/ES/en/technical-documents/protocol/genomics/pcr/extract-n-amp-product-guide) - [PCR/qPCR/dPCR Assay Design](https://www.sigmaaldrich.com/ES/en/technical-documents/protocol/genomics/pcr/pcr-qpcr-dpcr-assay-design) - [Cloning Troubleshooting](https://www.sigmaaldrich.com/ES/en/technical-documents/technical-article/genomics/cloning-and-expression/troubleshooting-for-molecular-cloning) - [Extract-N-Amp™ Plant PCR Kits](https://www.sigmaaldrich.com/ES/en/technical-documents/technical-article/genomics/dna-and-rna-purification/extract-n-amp-plant-kits) - [Ultrapure vs. DEPC Treated Water for Molecular Biology Applications](https://www.sigmaaldrich.com/ES/en/technical-documents/technical-article/genomics/dna-and-rna-purification/nuclease-free-water) - [Complete Solutions for PCR Assay Development](https://www.sigmaaldrich.com/ES/en/technical-documents/technical-article/genomics/dna-and-rna-purification/pcr-assay-development) - [Water for Nuclease-sensitive Molecular Biology Studies](https://www.sigmaaldrich.com/ES/en/technical-documents/technical-article/genomics/dna-and-rna-purification/water-for-nuclease-sensitive-molecular-biology-studies) - [Extract-N-Amp™ Tissue Feature](https://www.sigmaaldrich.com/ES/en/technical-documents/technical-article/genomics/dna-and-rna-purification/xnat-feature-article) - [View More](https://www.sigmaaldrich.com/ES/en/search/facet-search?focus=sitecontent&term=facet-search) Arriba __Inicie sesión para continuar.__ Para seguir leyendo, inicie sesión o cree una cuenta. Iniciar sesión__¿No tiene una cuenta?__Registrar An unknown error has occured. - Español - ES - English - EN [Más información](https://www.sigmaaldrich.com)