Extension Time In Pcr In Queens
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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 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.
Extension Time Extensions are normally performed at 68°C. As a general rule, use extension times of one minute per 1000 base pairs (e.g. 3 minutes for a 3 kb product) For products less than 1 kb, use 45-60 seconds. Products greater than 3 kb, or reactions using more than 30 cycles, may require longer extensions.
Increase the annealing temperature to improve specificity. The optimal annealing temperature is usually no less than 3–5°C below the lowest primer Tm. Optimize the annealing temperature stepwise in 1–2°C increments, using a gradient cycler when available. Consider touchdown PCR to enhance specificity.
Use 20–35 cycles. Use fewer cycles when template concentration is high, and use more cycles when template concentration is low. 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.
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).
Extension/Elongation Step The primers represent the starting point for the next step, called the extension step. During the extension, or elongation, step, Taq polymerase binds to each PCR primer and begins adding nucleotides. Note that Taq, like human DNA polymerase, can only add DNA nucleotides in one direction.
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.
The term "extension" is more commonly used in PCR protocols to describe this specific step, where the DNA strand is being extended. On the other hand, "elongation" emphasizes the process of the DNA strand progressively lengthening as nucleotides are added sequentially.
Polymerase chain reaction (PCR) is a method widely used in molecular biology to make many copies of a specific DNA segment. Using PCR, a single copy (or more) of a DNA sequence is exponentially amplified to generate thousands to millions of more copies of that particular DNA segment.
