Final answer:
Primers in PCR provide a starting point for DNA synthesis by annealing to target DNA strands, facilitating the DNA polymerase in synthesizing the new strands.
Step-by-step explanation:
The purpose of primers in PCR (Polymerase Chain Reaction) is to provide a starting point from which DNA can be synthesized. During PCR, heat is applied to denature or separate the double-stranded DNA into single strands. When the mixture cools, primers, which are short sequences of single-stranded DNA, anneal to each strand of the target DNA. These primers are complementary to the regions flanking the gene of interest, providing the necessary 3'-OH end upon which DNA polymerase can add nucleotides to synthesize new strands of DNA.
In this process, the DNA polymerase used is commonly Taq polymerase, which is heat-stable and can withstand the high temperatures required for DNA strand separation. Thus, PCR amplification can occur as the primers enable the DNA polymerase to replicate the target DNA in cycles of heating and cooling, a process automated by a device called a thermocycler.