During the polymerase chain reaction, the two DNA strands are separated at 95 °C, after which the reaction mixture is cooled to 54 °C to allow the primers to hybridize with the DNA strands. Why do parent DNA duplexes not form instead of the primer-template duplexes? The free nucleotides are present in such a large excess that they interfere with the parent strands coming back together. The primers are present in such a large excess that they outcompete the parent strands coming back together. A temperature of 54 °C is not sufficiently below the parent strands' Tm for them to recombine. The buffer conditions of a PCR reaction disfavor the formation of double-stranded DNA. The DNA polymerase binds to the single strands and prevents them from coming back together to form a double helix.
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The question asks why parent DNA duplexes don't reform during PCR after the strands are separated at 95°C and cooled to 54°C. The options provide several possible reasons. Show more…
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In a typical PCR reaction, the following stages occur at temperature ranges of 92-95°C. Heating to 92-95°C allows the primers to bind to the denatured DNA. Heating to 92-95°C allows the heat-stable DNA polymerase an opportunity to extend the primers by adding nucleotides to the 3' ends of each growing strand. Heating to 92-95°C denatures the double-stranded DNA so that it dissociates into single strands.
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In Polymerase Chain Reaction, one of the steps involves cooling the DNA to 55-65°C to allow specific DNA primers to bind to complementary sequences on DNA template strands. This step is
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Why is heating the first step in PCR amplification of extracted DNA? It permits hydrogen bonds between DNA strands to break. It is required for primers to bind permanently to the DNA. The nucleotides bind together at high heat. It is necessary for DNA strands to bind to each other. The enzyme DNA polymerase works at a higher temperature.
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