Final answer:
In PCR, the two primers are complementary to their specific target sequences on the separate strands of DNA, not to each other. They bind to the 3' ends of the strands, allowing the DNA polymerase to synthesize new DNA from these starting points.
Step-by-step explanation:
The two primers used in one PCR (Polymerase Chain Reaction) are not complementary to each other. Instead, they are complementary to their respective opposite strands of the DNA to be amplified. During a PCR cycle, the DNA strands are first separated by heating them to around 94°C.
Then, as the mixture cools to around 55°C, each primer anneals to its complementary sequence at the 3' end of the separated DNA strands. The top primer, also known as the forward primer, anneals to the bottom DNA strand, while the bottom primer, also known as the reverse primer, anneals to the top DNA strand. They provide starting points for the DNA polymerase to begin synthesis during the extension phase at approximately 72°C. The PCR technique relies heavily on the specific binding of these primers to the DNA template.