what is the role of dna polymerase in pcr
The role of DNA polymerase in PCR (Polymerase Chain Reaction) is to synthesize new strands of DNA by adding nucleotides to the existing template strands. PCR requires a heat-stable DNA polymerase, usually Taq polymerase, that can withstand the high temperatures used in the amplification cycles. During the extension step of each cycle, the DNA polymerase binds to the primers and adds nucleotides complementary to the template strand, extending the new DNA strands. This process is repeated for multiple cycles to amplify the DNA segment of interest. DNA polymerase plays a crucial role in enabling the success and efficiency of the PCR reaction.
The role of DNA polymerase in PCR (Polymerase Chain Reaction) is critical for the amplification of the target DNA sequence. Here's its step-by-step role:
1. Denaturation: In the first step of PCR, the reaction mixture is heated, causing the double-stranded DNA to denature (separate into two strands). DNA polymerase does not have an active role in this step.
2. Annealing: The reaction mixture is then cooled, allowing the primers (short DNA sequences that are complementary to the target DNA on the template strand) to anneal (bind) to their specific target sequences. DNA polymerase does not actively participate in this step either.
3. Extension: Once the primers are bound to their target regions, DNA polymerase is added to the reaction mixture. It synthesizes new DNA strands by adding nucleotides in the 5' to 3' direction using the existing DNA strands as templates. DNA polymerase catalyzes the extension or elongation step by adding complementary nucleotides to the primers, creating new double-stranded DNA molecules. The nucleotides are added to the 3' end of the primers, resulting in the replication of the target DNA segment. This step involves a DNA polymerase enzyme, such as Taq polymerase, which is commonly used in PCR.
4. Cycling: These three steps (denaturation, annealing, and extension) are repeated for multiple cycles to amplify the target DNA segment exponentially. Each cycle doubles the amount of DNA present, resulting in a significant increase in the target DNA quantity.
In summary, DNA polymerase is responsible for the extension step in PCR by adding nucleotides to the primers and synthesizing new DNA strands. This enables the amplification of the target DNA segment through multiple cycles of denaturation, annealing, and extension.