Which entry best defines polymerase chain reaction (PCR) as a method for amplifying a DNA base sequence, using a heat-stable polymerase and two primers?

Which entry best defines polymerase chain reaction (PCR) as a method for amplifying a DNA base sequence, using a heat-stable polymerase and two primers?

• A. Petechiae
• B. Polymerase chain reaction - a method for amplifying a DNA base sequence using a heat stable polymerase and two 20-base primers, one complementary to the (+) strand at one end of the sequence to be amplified and the other complementary to the (-) strand at the other end. Because the newly synthesized DNA strands can subsequently serve as additional templates for the same primer sequences, successive rounds of primer annealing, strand elongation, and dissociation produce rapid and highly specific amplification of the desired sequence in a DNA sample.
• C. Rokitansky Method
• D. Seminal

Answer: (B)

PCR is a technique that makes many copies of a specific DNA segment by cycling through heating and cooling steps. It requires a heat-stable DNA polymerase so the enzyme remains active during the high-temperature phase that separates the DNA strands. Two short primers, each designed to bind to opposite ends of the target sequence, are used to mark the region to be copied. In each cycle, the DNA is denatured, primers anneal to their complementary ends, and the polymerase extends from the primers to synthesize new strands. The newly made DNA strands then serve as templates for additional cycles, so the target sequence is amplified exponentially and with high specificity. This description directly captures the essential parts of PCR—the heat-stable polymerase, the two primers defining the ends, and the cycle-driven amplification—making it the best fit. The other options don’t describe a method for amplifying a DNA sequence: one is a skin finding (petechiae), another is a different named method not related to PCR, and the last is an unrelated term.

PCR is a technique that makes many copies of a specific DNA segment by cycling through heating and cooling steps. It requires a heat-stable DNA polymerase so the enzyme remains active during the high-temperature phase that separates the DNA strands. Two short primers, each designed to bind to opposite ends of the target sequence, are used to mark the region to be copied. In each cycle, the DNA is denatured, primers anneal to their complementary ends, and the polymerase extends from the primers to synthesize new strands. The newly made DNA strands then serve as templates for additional cycles, so the target sequence is amplified exponentially and with high specificity. This description directly captures the essential parts of PCR—the heat-stable polymerase, the two primers defining the ends, and the cycle-driven amplification—making it the best fit.

The other options don’t describe a method for amplifying a DNA sequence: one is a skin finding (petechiae), another is a different named method not related to PCR, and the last is an unrelated term.