What is the role of primers in PCR?

• A. They unwind DNA.
• B. They provide starting points for DNA synthesis.
• C. They degrade RNA primers.
• D. They cut DNA.

Answer: (B)

Primers provide starting points for DNA synthesis. In PCR, the DNA strands are first separated by heat, and short DNA primers bind to complementary sequences at the ends of the target region. DNA polymerase can only add nucleotides to an existing 3' end, so the primers supply the necessary starting points for extension in the 5' to 3' direction. By binding to sequences flanking the region of interest, primers determine what gets copied and enable exponential amplification of that specific segment across cycles.