Final answer:
In PCR, the primers anneal to specific sequences in the DNA, marking the beginning and end of the amplification product. They are essential because they provide the starting point for DNA polymerase to synthesize new strands of DNA during PCR cycles.
Step-by-step explanation:
The area where the primers bind in Polymerase Chain Reaction (PCR) denotes the beginning and end of the PCR product and is called primers annealing sites. Primers are short DNA sequences that are complementary to the target DNA sequence, allowing for the initiation of DNA synthesis by DNA polymerase. In PCR, the primers delineate the section of DNA to be copied.
Primers bind to specific locations on the DNA strand, and these locations mark the starting points for the new DNA strands that are to be synthesized during PCR amplification. The primer that anneals against the bottom DNA strand is known as the bottom primer, and the one that anneals against the top DNA strand is termed the top primer. After heating the DNA to separate the strands, the primers quickly anneal to the corresponding complementary 3' ends of the DNA template when cooled.
Because the primers define the boundaries of the DNA region to be amplified, during the initial PCR cycle, the product extends beyond the desired DNA segment. In subsequent cycles, however, the desired PCR product is synthesized more efficiently as primer annealing becomes more specific to the previously amplified DNA regions. Therefore, primers annealing sites are crucial for obtaining the correct PCR product.