Final answer:
Uracil-N-glycosylase (UNG) is utilized in PCR to degrade uracil-containing DNA to prevent contamination from previous PCR reactions while having no effect on the new DNA synthesis.
Step-by-step explanation:
The use of uracil-N-glycosylase (UNG) in PCR (Polymerase Chain Reaction) is to prevent carryover contamination from previous PCR reactions. UNG degrades uracil-containing DNA present from previous PCR amplifications. Since PCR typically uses thymine rather than uracil in DNA, UNG selectively targets only contaminant DNA that has uracil, resulting from previous reactions where dUTP might have been used instead of dTTP. This ensures that the amplification in the current PCR is from the new template rather than from possible contaminants. UNG is usually inactivated by heat before the actual PCR amplification begins, which prevents it from degrading the newly synthesized DNA that may contain uracil.