Extension Time In Pcr In Suffolk
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Extension is achieved by using the loosened nucleotides of each base to grow the complementary DNA strand. The end result is two double-stranded products of DNA. The temperature that is used during the extension phase is dependent on the DNA polymerase that is used.
Increasing the final extension time improves full-length replication and yield of a 0.7-kb, GC-rich PCR fragment from human gDNA in these experiments. The smear under the desired band in 0 minute final extension suggests incomplete extension of the PCR amplicon by the DNA polymerase.
The third step in a PCR cycle is the extension step. The extension step, also referred to as the elongation step, is the PCR step in which Taq polymerase adds nucleotides to the annealed primer. The process of repeating the denaturation, annealing and extension steps of PCR is known as PCR cycling.
Final Extension A post-PCR final incubation step of 5–10 min at 72°C is often recommended to promote complete synthesis of all PCR products.
The extension time of PCR depends upon the synthesis rate of DNA polymerase and the length of target DNA. The typical extension time for Taq DNA Polymerase is 1 min/kb, whereas that of Pfu DNA polymerase is 2 min/kb.
Many of the common problems with PCR and RT-PCR are identified during agarose gel electrophoresis of the reaction products. These include the absence of the expected amplification product, the presence of nonspecific products, excessive smearing, and the presence of a “primer dimer” band.
If the extension time is too short, there will be insufficient time for complete replication of the target. Generally, use an extension time of 1 min/kb. If the annealing time is too short, primers do not have enough time to bind to the template. Use an annealing time of at least 30 sec.
The final stage is the extension step (20 sec to 1 min at 72 °C), which is performed so that the DNA polymerase extends the primer sequences from the 3' of each primer to the end of the amplicon. A 1 min extension is typically sufficient to synthesize PCR fragments up to 2 kilobases (kb).
Initial Denaturation for 2 minutes at 94°C. Denature for 30 seconds at 94°C. Anneal primers for 30 seconds at 55°C (or 5°C below Tm). Extend DNA for 2 minutes at 72°C.
